123 PIC Microcontroller Experiments for the Evil Genius

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Evil6eniu5series 123Robotics Experimentsfor the Evil Genius Electrcnic Gad|etsfot the Evit Genius:28Build'it'yourself Prciec! Electonic Ci/cuits for the Eril GeniL.s:57Lesso^, with Prciects 123 PI(P Microcotltollel Eryeriments fol the Eril Geniut Mechatonics fol the Et il Genius:25 Build-it'youtself Prcject' 50AwesomeAutomoli'e Prcjectsfor the EviI Genius Sotat Energ! Proiectsfor the Evil Genius:16 Buikl'it'yoarselfThemoelectic MechdnicalPrcjects

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Mitrrotrontroller Experiments for the Evi| 6enius MYKE PREDKO

McCraly-Hill New York Chicago SanFrancisco Lisbon London Madid Mexico Cily Milan New Dcthi SanJuan Seoul Singapore SydDey Toronlo

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copyrightO 2005byTheMcCraw-Hill CommpinicqInc.All rightsfcscrvedPrinledin thc UniredStolesorAnerica.Exceplaspermittedundcrthe UniledStalcsCoPvrightAct of 1976'to or dislributedin nnyforn or by anymcan$,otslored pnn of thispublicationmaybe reproduced in a dalabaseor rotricvalsyftD.vilhout theprif writLenpcrnhskn ol rhepublishcr' 3 4 5 6 7 8 9 0 Q P D / Q P D0 I 0 9 l J 7 ISBN 0-07145142-0 Thesponhtug edint lot thi\ hook trasJkd!)Bisr Ml the?roductiontttll!tui$r LLC ThcIrt dituctorJol easPMtle A. Pelton.ft wat NetibTinw Tat by l kAllistet PttblishiSService!, th! &v0 ,,a! Ahthory kndi. Ptink anl hantl bt Qu.h.cot/Dubuque.

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Acknowledgments About the Author

SectionOne Underthe Coversof the PIC16F684 EXPERIMBNT1

I/OPins

EXPERIMENT 2

Configuration word

EXPERIMENT 4

PIC MCU Variable Memory,Registers, and ProgramMemory in Simulating cFlash.c MPLAB IDE

SectionTko IntroductoryC Programming

t3

18

27

C DataTypes

29

EXPERTMENT 7

ConstantFormatting

31

EXIERTMENT10 EXPERTMENT 11 EX?ERTMENT12

EX?ERTMENT13

ConditionalLooping

45

EXPERIMENT 16

TheFor Statement

46

Assignment Statements Expressions lJrtwrse uperators

33 35

LogicalExpressions ConditionalExecution Usingthe If Statement 39 NestedConditional Statements

SectionThree SimplePIC@MCU Applications 51 EXPERTMENT 17

BasicDelays

53

EXPERTMENT 18

PTCkit1 Sequencing StarterKit LEDS

55

BinaryNumberOutput UsingPICkit 1 Starter Kit LEDS

56

EXPERIMENT 20

BasicButtonInputs

58

EXPBRTMEN'r21

DebouncingButtonInputs 59

EXPBRIMENT22

MCLR Operatiorl

6I

EXPBRIMENT23

EndingApplications

63

EXPERIMENT 19

20

EX?ERIMENT6

EXPERIMENT9

EXPERTMENT 15

L4

28

EXPERIMENT8

43

x

VariableDeclaralion Statements

EXPERIMENT 5

q.f,

TheSwitchDecision Statement

EX?ERMENT14

t

Introduction

EXPERTMENT 3

ix

SectionFour C Language Features67 EXPERIMENT24

Functions andSubroutines 69

EXPERTMENT25

GlobalandLocalVariables70

EXPERIMENT26

Defi[esandMacros

7I

EXPERIMENT27

VadableAuays

73

EXPERIMENT28

Structures andUnions

75

EXPERTMEN.T 29

PointersandLists

'76

EXPERTMENT30

Character Strings

79

EXPERIMENT 31

LibraryFunctions

81

4I

SectionFlve PIC16F684Microcontroller 89 Built-in Functions ExPERrrtNT32 Brownout Reset

91

ADC Opcratiotl EXTERIMENT'33

93

34 ComparatolOperation EXpERINIENT

96

EXPER|"I|NT35 Watchdog'l'imer

99

36 ExpERlNlFrNr

Short Timer Delays

UsingTMRo 37 Exr,r,RrNrENr'

Usingl'MRt ComparingClock Oscillators

106

r'40 Pin Rcsislarce LlxPEnt\'lr-tN

t09

PwM SignirlJl t l | 41 Cunerirung F\11 RrN,rE\

Rcaction-TimeTester

140

52 ExPERltvtENT

Rokenbok@Monorail/ Tiaffic Lights

143

LED Seven-Segment Thelmometer

t46

PIC MCU "Piano"

151

Model Railway Switch Colltrol

lfJ

54 EXPDRIMENT

56 PC OperatingStatus ExPERIMENT Display

ExIERIMENT57 Thc asmTemplate.asm

SectionSix Interl'acingProjectsfor the PIC@Microcontroller ll'7

58 ExPERIMENT

ExpLRIMEN]43 Driving a Scvcn_Segmcnt

59 Loadingthe WREG and EXPERTMENT

L\"r Rr\I N"4 |

45 ExPERTMENT

LED Matrix DisPlaYS

,16 LCD Display EXPERTMENT ,lT ExpFtRrNrENl

Filc ard BasicDirectivcs 160

124 126

ProduciDg Random Numbers

128

ExpERrvrENr,l8

Two-Bit LCD Display

129

EXPERI4nNT49

Switch Matrix KeYPad MaPPing

t31

SpecifyingProgram MemoryAddresses

161

SavingIts Coitents

164

60 ExPERtMENT'

Detining Variables

165

6l EXI,ERIMENT

Bitwiselnstructions'i6'7

62 EXPLRTMENT

Additionlnstruclions

168

63 EXPERIMENT

AddLibs: Strange SimulatorResults

170

ll9

M u l t i l ' l cS c v q n - S c g m c t r t 121 LED Displays

156

SectionEisht Introductionto PIC@ MCU Assembly Language 159 Programming

I 42 StolingandRctrieving Exl,r-rRrN4BN t14 Data

DirectlY I-ED DisPlaY homthcPICl6F6U4

.

51 EXPERTMENT

EXlrinrMENT55

104

Mcasulcmcnts

LED Display 138 Pumpkin

53 EXPERIMENT

102 Usiig theTMRoPrescaler

137

50 EXPERTMENT

101

Exl,trtIMENr'38 LongTlnler Delays

f 39 ExPERTMEN

Section Seven SampleC Microcontroller Applications

64 EXPERIMEh*T

Sublractionlnstructions

65 EXPERTMENT

Bank Addressing

Bit lnstructions EXPERTMENT'66

Contents

']71 173 1'75

EXPERTMENT 67

r7'7

Bit Skip Instructions

EXPERIMEh-r 68

ConditionalExecution

178

EXfERTMENT 69

declszLooping

180

EXPERTMENT 70

Subroutines

181

EXPERTMENT 7l

Defining and ImplementingArrays

EXPERTMENT86 PIC MCU Instrument Interface

231

EXPERTMENT8T SoundDetection

235

EXPERTMENT 88 Multiple Miqoswitch Debouncing EXPERTMENT 89 EXPERIMENT 90

EXPERIMENT 72

LogicSimulation Using thePlC16F684

EXPER]MENT 73 TheC "Switch" Statcmont

188

191,

ExPEnIMENT74

Dcfines

ExPEnTNIENT 75

ConditionalAssembly 197

ExPERti\4ENr 76

Macros

194

199

EXPERIMEN].77l6-BitValues/Variables 201 ExPEnTMENT 78 EXPERIMENT 79 EXPERIMENT 80

UniversalDelayMacro 203 High-lavcl Pro$amming 205 lmplementing Read-Only 208

AIrays EXPERIMENT 8l

Data Stacks

210

EXPERTMENT 82

CircularBuffers

212

EXPERTMENT 83 Readingandw ting the

EEPROM Data Memory 214

SectionTen Sensors ExPERrMENr34PIC MCU BS2User lnterfacc

227 224

EXPERTMENT 85 PIC MCU BS2Keypad Interface 230

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Light Sensors

23'7 238

I82

SectionNine PIC@Microcontroller AssemblyLanguage '187 ResourceRoutines

f"\

Infiared (IR) Surface Sensor

239

ExpERlMENr9l Intcrfacing10Shary cP2D120 Rangirg Object Sensors

242

ExPERTMENT 92 Do-lt-Yourself IR Object Sensor

243

ExPERTMENT' 93 lR Object-Ranging Sensor

24'7

ExpERTMENT 94 UltrasonicDistancoRangeSensor

249

ExPERrMENr95RoborIRTag

251

SectionDleven Motor Control

255

EXPERIMENT 96 DCMotor Driven Usi g the CCPPWM and Using a Potentiometer Control 257 E x P f R r v F \ r1 , 7 D C M o t o rC o n t r oxl i l t SimpleTMR0 PWM

261

ExpERIMENT98ControllingMultiple Motors with PWM aDd Bs2lntcdace

264

EXPERIMENT 99 Bipolar StepperMotor Control

265

EXpERIMENT 100 UnipolarStepperMotor Control 269 EXPERIMENT 101 Radio-Control Model Scrvo

Control EXPERTMENT 102 Multiple ServoControl SoftwareStructure

Contents

272 2'74

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RobotBase 103Two-Servo EXPERTMENT 27'7 withBs2lnterface SectionTwelve SolvingProgramming Problemsin PIC@ Microcontroller AssemblyLanguage279 t ultiplicatitrn E \ p r R r M\rr 1 0 4 L i g h l - B iM with a 16-BitProduct 280 ExpERrMENl105 Division of a 16-Bitvalue by an Eight-Bil Valuc 282 a NumberUsing | lu6 Squrring Exr,r'RrMr'\ Finite DifferenceTheory 284 107 Find lhe SquareRool of a EXPERTMENT 28(t 16-BitNumber 108 Converlinga Byte into EXPERIMENT Hex, Three Decimal,T\'r'o Eight Binary ASCII or 289 Bytes 109 Produccthe Even Parity EXPERTMBNT 291 Valuesfor a Byte 1 I0 Sort a List of 10Eight-Bit EXPERTMENT ValuesUsingthe Bubble292 SortAlgo tllrn EXpERIMENT 111 Encrypt and Decrypt ull ASCIIZ SlringUsing a SimpleSubstitution 294 Algolithm E x p E R r \\4r lrl 2

Number Sequence

113 Find the LargestCommon EXPERTMENT FactorofTwo Eight-Bit

Numbers

298

SectionThirteen ZipZaps@Robot 301 EXPERIMEN T 114 Characte zing the

Zipzaps

303

PIC MCU PowerSupply 305 EXPERTMENT'115 116 EXPERTMENT

PIC MCU Electronics 307 PCB

I 17 EXPERIMF,NT

IRTV RemoteControl 310

I18 EXPERIMENT

Molor andSteering Control

311

119 EXPERTMENT

BasicThsk-Control Software

120 EXl ERTMENT

lR RemoteContlol

121 ExPERTMENT

and Lighl Sensors Followirlg

122 EXPERTMENT'

IR ObjectDetection 318 Sensors

123 ExPERTMENT

IR Linc-Followirlg Sensors

Index

C c n e r a t ce F i h o n a c c i

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29'7

Contents

316

320

327

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FcknouJledgments

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q My edilor at Mccraw-Hill, JudyBass,who consistentlyrespondsto my questionsand suggestions, regardlessof how dunb they are, with good humor and thougltfulness.

This book would not have been possiblewithout t1le help, suggestions,and time from the fbllowing indi viduals: . CarolPopovich,Greg ADderson,Joc Drzewiecki,AndreNemat,and Fanic Duven$ho ha\e helpednre hageol I\4i(rochrn understandwhich productswould be besl suitedfor this book,and havebeenwilliDgto .pcndrimewith me lo undersrand my rcquircand m9nts,answermy legionsof questions, suggestavenuesto follow that hadn't occurred

supportstallfbr HT-Softandlhcir technical quicklyandholping D'ryqucstions answering to cxplailtheiDnerworkingsofthe PICC is Lirccomtiler.The PICC.linc of compilers proand tool for thebcginnct a lrcmcndous lo re.lc:)iunrlrlikc,andoneTncvcrhcsitatc onmlcDCl. andlhes!uBradNorth,RichardBonafede, Schoolilr dentsot RickHansenSccondary Onf.lrio,lbrhelpingmeto learn Missassauga, learn moreabouthowstudenls(andteachers) andthc PIC electronics, aboutprogramming, MCU BlairClarksonaDdDnvcPiloleat the Oltario pushingmeto CentreinToronlo,I'or Sciencc concepts to peoexplairbasicmicrocontroller Sumo" plethatluve built theTAB Electronics Botat a workshopandwantto do norc with ir. lhe BS2i rt'rfaccandRobotIR Tig cxpcrimentsarea direclresultofthiswork.

lo bc oneol lhd be(l lhc PIC MCU continucs .uppo cd dc! ice.on lir)e.3ndI !\ouldlike lo thalk the many individualswho havetaken the time lo put informationand projectson rhe lnlefncla\ \rcll assupporlandhclpntheN trying to better undclstandthe PIC MCU or get their applicalionsup and ruDning.

.

fbr ideas,answcrs Celeslica anditsemployccs questions, to and opPortunities to straDge expandmy lcchnicalhorizons,

.

My daughterMarya,whohasgrownup with a fatherlhatis alwaystryingout ncwprojecls on hcr.Shctricsthemout wilh cnlhusiasm needa bit of despitethclhcl theygenorolly tuningbelorctheyworkperlcctly.

.

for kecpingeverything My wilc Patience, daughler cvcnwhenour youngcst togethcr, Talithawassick,andfor havingdinneron the slove,evcnwilh measkinghc! 10do a"quick read"of a sectionor two.I couldn'tdo anyof it withoulyou.

To all ofyou,thankyoufor all youunselfishhelP expcdences, and andwillingness 1()shareyourideas, enlhusiasm for lhisbook. mgke

Acknouledgments

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in Torontq Canada,a supplielof printedcircuitboardsto the comMyke hedko isTestArchitectat Celestica, 123Robotitr Prcjectsfor theEvil puterindustry.Aln expedenced author,Myke wroteMccraw'Hill's best-selling Progammingand CustomizingPICMirrc Microconlrolkrs, Genius;PICmicrcMictocontoller PocketRefercnce; RobotContollers;andotherbooks,andis theprincipaldesignerof bothTAB SecondEdition;P/oSramming EElecironics BuiM your Ov,nRobot kits,

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About the Author

Introduction When I wrote my first book on the Microchip PICP microcontroller (commonly abbreviated to "MCU") almost10 yearsago,the mostcommoncriticismI receivedaboutthe book wasthat it took too long to get to the projects.This is quite foreign to me becauseI tend to leam a new device,like a microconftoller,by first reviewingthe datasheets for the part's electrical information,workingat understandingthe architecture andhow it is programmed,and endingwith understandingwhat kind of developmenttools are availablefor the part.Looking over this list of tasks,it is quite obviousthat they cameaboutwith my backgroundand training.Being a teenagerin the 1970sand goingto universityin the early 1980qtherewasn'tthe variety of easy-to-work-with devicesthat are available today,and the sophisticated personalcomputer-based developmenttools that we take for grantedwerenot evenbeingconsidered, let alonebeingdevelopedor sold.My method for learning about a new part is effective for me and a result of the situation I found rnyself in when I first started working with electronics Today you can setup a development"lab" and createa basic applicationfrom scratchfor the PIC MCU in lessthan 20 minutes usingMicrochip's MPLAB@integrated developmentmvironmmt (IDE) andPlckitrM 1 starterkit with HT:.soft'sPICC LiterM c compiler. The purposeof this book is to introduceyou to the MicrochipPIC MCU and help you understandhow to createyour own applications. In this introduction, using the PICkit 1 sl2irterkit printed circuit board. (PCB) andfree developmenttoolsfrom Microchip andHT-Soft,I will showyou how easyit is to createa simplePIC MCU programthat will flashone of the light-emitting diodas (LEDs) on the PICkit 1 starter kit. As you work throughthe book,your understanding of the PIC devicewill increaseto the point where you shouldbe comfortablecreatingyour own complex applications in both the C programming languageaswell asassemblylanguage. The PICkit 1 starterkit (seeFigurei-1) contains everythingyou will needto leam how to createand testyour own PIC MCU applications. This includesa programmerPCB (seeFigurei-2), a universalserial bas (USB) cableto connectthe PICkit 1 starterkit to your PC,a CD-ROM containingthe sourcecodefor the applicationspresentedin this book,two PIC MCUs,an eight-pinPIC12F675,and a 14-pin PIC16F684. In this book,I will be focusingon the PIC16F684becauseits 14pins allow a greatervariety of different applicationsto be built from it, but you will also gain experiencewith the eight-pin PIC12F675.

On the back coverof the book is a web link that you canuseto order a PICkit 1 starterkit for usewith this book.If you do not buy a PICkit 1 starterkit, the sourcecodecanbe dolrinloadedfrom my web site (www.myke.com). In this book, I will be working exclusivelywith Microsoft Windows.I recorrmend that you use the latestversionavailable(at this witing it is Windows,XP SP2)whenworking with the PICC Lite compilerand MPLAB IDE tools usedin the book.Development toolsare availablefor Linux, althoughnot for Apple MacintoshOS/X (but you shouldbe ableto get the Windowssoftwareto work from an emulator).You will find that the softwareworks well underWindows. If you look at the CD-ROMSthat comewith the PICkit 1 starterkit, you will find they havethe MicrochipMPLAB IDE and HT:Soft PICC Lite compiler developmenttools that are usedin the book. Although you could load theseprogramsonto your PC,I recommendthat you downloadthe latestversionsfrom the Microchip and HT-Softweb sites.These tools are continuouslyupdated(duringthe period that this book waswritten,MPLAB IDE had five upgrades, two of them major and changedhow someof the operationsare performed)to includenew featuresand PIC MCU part numbers,and to fix any outstandingproblems.In this book. I usedMPLAB IDE version7.01

Figure il The Microchip PICkit I stsrterkit enablesyou to createyour own PIC MCU applications and to testthem out easily qnd inexpensively.

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and PICC Lite compilerversion8.05.With the versions that you use,you may seesomedifferencesin look or operation,but the featurespresentedin this book will all be present.If you are confusedasto how to perform someoperation,you canconsultthe T[torial sectionof MPLAB IDE, which canbe found under the Help pull-down. To start settingup the softwareneededto start go to developingyour own PIC MCU applications, www.htsoft.com, asshownin Figurei-3.PICC Lite is a free,full-featuredC compilerthat supportsquite a few of the differentPIC MCU part numbers(includingthe PIC12F675and PIC16F684includedin the PICkit 1 starterkit package).Next click "Downloads"and then select"PICC Lite (Windows)"(seeFigurei-4).To downloadPICC Lite compiler,you will haveto register with HT-Softat no charge(seeFigurei-5).To do this,follow the instructionson the pageshownin Figurei-4.It shouldgo without sayingthat the page will probablynot look exactlylike the figureshere,due to the delaybetweenwhen I havewritten this and whenyou actuallyaccessthe web site. The retail PICC compileris capableof building codefor literally all the PIC MCU part numbersand doesnot haveany of the restrictionsof the PICC Lite compiler. After registering,the PICC Lite compilerinstallation softwareshouldstart downloadingautomatically. Dependingon your secudtysettings(especiallyif you useMicrosoftWindows/XPServicePack2 or later), the downloadmay be blocked(asin Figurei-6). If this is the case,you may haveto tum off the securityto allow the downloadto take place.Oncethe program hasdownloaded,I recommendselecting"Run" instead of"Save" (seeFigurei-7).Thiswill installthe PICC

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Lite compilerwithout leavingyou with an .exeor .zip file to deletelater. When the PICC Lite compilerinstallationscreen appears(seeFigurei-8),click "Next" and follow the defaults.If you are promptedto load the software/ driversfor MPLAB IDE, do so,asthey will be requiredto usePICC Lite compilerwith the Microchip tools andprovideyou with a truly integrateddevelopmentenvironment,or IDE. The MPLAB IDE is a singleprogramcontainingan editor, assembler, linker,simulator,and PICkit 1 starterkit's programmerinterface,and it will be the only program you haveto run to createPIC MCU applications. PICC Lite compilerwill integratewith MPLAB IDE whenthe latter is installedso you will havea single Windowsprogramfor developingC and assemblylanguageprograms for the PIC MCU. After PICC Lite compileris installed,you will be askedif you want to restartyour computer.Click "No," then powerdown your computer,and power back up.I find that soft resets(onesin which poweris

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With the PC backup,go to Microchip'sweb site (www.microchip.com shownin Figurei-9) and click "MPLAB IDE" or "DevelopmentTools,"followed by "Full Install" (seeFigurei-10).TheMPLAB IDE softwareis quite large(30 MB) andwill take sometime to downloadif you usea dial-upconnection.This time click "Save"insteadof "Run" and store the .zipfile into a temporaryfolder on your PC (seeFigurei-11).You shouldbe ableto unzip the file by double-clickingon it, and the file management softwareon your PC will expandthe file into the directory of your choosing(ideallythe sameone you startedwith). After the MPLAB IDE installfiles are unzipped, double-clickon "Setup" and follow the instructionsto insrallthe MPLAB IDE (seeFigurei-12).If asked, make surethe programminginterfacefor the PICkit 1 starterkit is includedand you will not haveto look at

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Figure i-ll Step9 - MPLAB IDE Installfiles stored in a temporaryfolder

any readmefiles (unlessyou want to). If you are promptedto reboot your computer,click "No" and then power down andpower back up,asyou did after installingthe PICC Lite compilersoftware.Do not connectthe PICkit 1 starterkit to your PC usingthe USB cableuntil you are told. That'sit;you've just installeda set of integrated developmenttoolsthat arejust aspowerful assome softwaredevelopmentproductsthat costmany thousandsof dollars.Withthe toolsinstalled,you can copy the sourcecodefiles for the applicationcodeusedin this book from the PICkit 1 starterkit's CD-ROM codefolder into a similar"code" or "Evil Genius" folder under the C drive of your PC.Another source for thesefilescan be found on my web siteat www.myke.com.

l , P 3 P I C @l ' l C UE x o e r i m e n t s f o r

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6enius

r{ q f*i: i.{

$-i*

kr. Figure i-12 Step10 - MPLAB IDE Installer window

Fisure i-13 Step11 - MPLAB IDE Start Up desktop

Now let's try to createa simpleprogramthat flashes an LED on the PICkit 1 starterkit. To do this,doubleclick on the MPLAB IDE icon that hasbeenplacedon your PC'sdesktop.Whenit first bootsup,the MPLAB IDE desktoplookslike Figurei-13,and is readyfor you to startenteringyour own application.Click "New" andenterthe following codeinto the window that comesup: #incluale -CONEIG(FCITDIS

& IESODIS

& BORDIS & IINPROIECT

!4CIJRDIS & P!\IRTEN & WMDIS int it nain( )

& INTIO)

'

t PORTA = 0; CUCONo = ?t ANSE J = 0i TRISA{ = 0i TRISAs = 0t (1 == 1) while

Figure iJq Step12 - FirstApplicqtion enteredinto MPLAB IDE Editor wind.owand savetl

{ f o r ( i = 0 r i < R A { = A A 4 ^ 1 t

25000r i++) i

Different partsof this programwill be displayed usingdifferentcolors;don't worry if it looks a bit strange.Theprogramshouldbe savedas"c:\Evil Genius\Flash\Flash.c" (seeFigurei-14).Oncethe programis saved,closethe window that containsit. All programsshouldbe run aspart of an MPLAB IDE projectthat savesoptionsandfeaturesselections specificto the application without requiring you to reloadthem eachtime you start up MPLAB IDE.The first stepis to specifythe projectnameand whereit is goingto be stored(seeFigurei-15).

Figurei-I5 prolect

Introduction

Stepl3 - Creating an MPLAB IDE

r'1 .-i

Figure i-'f6 Step14 - Selectingthe PICC Lite C Compileras the MPLAB IDE Buiki tool

Figure i-18 Step16 - Selectingthe PIC MCU part numberto work with (notethe largenumberof PIC MCUs to choosefrom).

The Flashapplicationis written in the C programming languagefor the PICC Lite compiler.To specify the PICC Lite compiler,click "Project" and then "SelectLanguageToolsuite."Youmay haveto scroll throughthe Active Toolsuiteto find PICC Lite compiler (seeFigurei-16).When you haveselectedit, makesurethat the locationof PICL.exeis correct.If it is not, look for the CIPICCLITE folder on your PC, and point the ToolsuiteContentsto picl.exein the BIN subfolder. When you are working with assemblylanguageprograms,you may haveto perform the sameoperation thereaswell. In this case,the assemblylanguageprograms(suchasmpasmwin.exe) canbe found in the ProgramFiles\MPLAB folder or in its subfolders. Right-clickon "SourceFiles"in the Flash.mcwwindow (seeFigurei-17) and select"Flash.c"from the

folder (whereyou stored c:\Evil Genius\Flash\Flash.c the programearlier).Toload Flash.conto the desktop, double-clickon "Flash.c"in the Flash.mcwwindow. Flash.cwith the projectthat was This will associate just created.Each time you work with a new program,it shouldhavea new projectassociated with it. Next,you will haveto make surethe proper PIC MCU is selectedfor the application.CLick"Configure" and then "SelectDevice,"and find PIC16F684in the list (seeFigurei-18).I'm sureyou will be amazedat the numberof differentPIC microcontrollerpart numbersthat comeup.After working throughthis book,you will discoveryou can programand usethe The vastmajodty of thesechipsin your applications. differencein the part numbersis the numberof pins and interfacingfeaturesbuilt into the PIC MCU. Programmingand interfacingare identicalto what has beenpresentedin this book. Now you are readyto try and "build" the application.You canclick "Project" and then "Build All," or pressCtrl+F10to compilethe applicationand store the resultin a .hexfile that will be programmedinto the PIC MCU later.If any errorsoccur,go back over the codeyou keyedin and compareit to the previous Iisting.Thisis the mostlikely sourceof the problem. Oncethe programhascompiledcorrectly,you will get the summaryinformationshownin Figurei-19,listing the amountof spacerequiredto storeand run the programin a PIC MCU With the programcompiled,plug your PICkit 1 starterkit into a USB cablepluggedinto your PC. Afterwards,the MPLAB IDE screenwill look like Figure i-20with the statuswindow changingto list the Firmwareversionof the PICkit 1 starterkit. If it does

, a:": :

l

.i.,u

,:-,) :t,,1 ir.,.':

Figure i-17 Step15 - Specifyingprojectsourcelile

5

l , a 3 P I C @I ' l ( U E x o e n i m e n t s f o r

the Evil

6enius

Figure i-19 Step17 - Build informationfor "Flash.c"application

not change,then click on the programmer toolbar loIlowedby "SelectProgrammer"and then the PICkit 1 icon.A four-buttonprogrammertoolbar will alsobe displayedon the desktop.Removethe PIC12F675that cameinstalledin the PICkit 1 starterkit and put in the PIC16F684that wasin the PICkit box.Rememberto storethe PIC12F675in a safeplace(usingthe pieceof foam the PIC16F684wason is a goodchoice).Click "Programmer,""Program Device,"or the Program icon (placeyour mouseover the programmericonsto makea button legendappear)to downloadthe applicationinlo lhe PICl6F684.The programming operation will take a few moments(the operationis indicated by a growing bar on the bottom-left corner of the desktop,and a "ProgramSucceeded"message will be shownon the statuswindow,Figurei-21). Oncethe build/compileoperationqfollowedby the deviceprogrammingsteps,are complete,the D0 LED of the PICkit 1 starterkit will start to flash.If it doesn't,you shouldreviewthe sourcecodeand the processof creatingthe project.

Figure i-eO Step I8 - tnformarionprovitled when the PICkit 1 starter kit is pluggedinto the (levelopment PC's USB Port.Note:Four-buttonProgrammer toolbar at the top centerof MPLAB IDE desktop.

Introduction

(evenif it's flashingan LED, asI do in this introduction).The secondtime it will take half aslong,the third a quarter,and so on. Over a fairly short period of time, you will be ableto createapplicationsefficientlythat asthosecreatedby professionals. are assophisticated

Figure i-al Step19 - Thefirst applicationhasbeen programmedinto a PIC16F684and insertedinto the PICkit 1 startedkit connectedto the developmentPC. TheD0 LED shouldnow beflashing!

Seeingyour own PIC microcontrollerapplications working will be an amazingexperiencefor you,and it will give you a senseof pride to know you can do somethingthat only a smallpercentageof the world's populationcan do.Unfortunately,the processof getting thereis full ol frustration,confusion,and hard work.Along with teachingyou about the PIC MCU, the purposeof this book is to help you gain the skills necessary to developyour own applicationswith a minirnumof the inevitablefrustration.confusion,and hard work.

Prerequisites That'sit;you havejust set up a very sophisticated microcontrollerapplicationcodedevelopmentlab and createdyour first application.I realizevery little of the programor the processyou went throughto get to this point makessense,but asyou work throughthe different expedmentsin this book,their functionswill becomemore obviousand easierfor you to useon your own.Justasif you wereto reviewthe datasheets for the part'selectricalinformation,working at understandingthe architectureand how it is programmed will help you understandwhat kind of development tools are availablefor the part. Throughoutthe rest of this book,I will help you learn aboutand work with the PIC MCU. The experimentsrangefrom the very trivial to somevery complex intedacingapplicationsthat are really quite a bit of fun.Thereis a lot of materialin this book and a lot to learn;try to work througheachexperimentin a sectionbeforetaking a break-I would be surprisedif you were ableto get throughthe entirebook in less than a year. As part of the learningexercise,try to developyour own circuitsandcode-this will cementthe knowledge you gainfrom the book and help you build the skills neededto createyour own applications. Don't be afraid to usemy designsand codeasa baseor asa part of yours (usingcut and paste).Playing"what if" can be a lot of fun and very instructive.I believethat before somebodyis comfortableworking on a new deviceand developmentsystem,he or sheshouldhave50 or so of his own applicationsunder his or her belt. Don't be discouragedwhen,at first,your applicationsdon't work.It isn't unusualfor it to take a week or two to get a person'svery fint applicationworking

This book waswritten to be the secondin a sequence (123RoboticsExperiments for theEvil Geniusvtasthe first book) and,assuch,many of the basicelectrical, mechanical, and programmingconceptsusedin this book werepresentedin the first.To understandfully the experimentspresentedin this book aswell to be you will haveto ableto createyour own applications, be familiar with the conceptslistedbelow: .

Basicelectricallaws . Partsof a circuit . Ohm'slaw . . .

Seriesresistances Parallelresistances Kirchoff'svoltagelaw

.

Kirchoff's current law

o

Thevinin'sequivalency Resistormarkings

o .

Semiconductorbasics . Diode operation . LEDs (including7 SegmentDisplays) . Bipolar transistoroperationand pinouts . MOSFET operation

.

Binary electroniclogic . The six basicgates . Diflerentlogictechnologies . . .

l , e 3 P I C o l l C l JE x p e n i m e n t s f o r

The Booleanarithmeticlaws Typesof flip flops Commoncircuits

the Evil

Genius

. o . o

Adders Muxes/Demuxes Counters Shift registersand.linearfeedbackshift registers(LFSRs)

Oscillators . Basicrelaxationoscillator o

Reflexoscillator

. .

Crystalsandceramicresonators 555timer chip Common electronicdevices . 74L op amp . 386audioamplifier .

IR objectsensors Powersupplies . Batteries . 780x/78l0xvoltageregulators .

Switchmodepower supplies Numberingsystems . Scientificnotation . Metdc prefixes r . .

Capacitormarkings Binary numbersand conversions

Hexadecimal numbersandconversions Programmingconcepts . Data types r . .

Variabledeclaration Assignmentstatement Vadablearrays

.

Iflelse/endifstatement

.

While statement

o

Subroutines Microcontroller concepts . Memory organization . .

Input and output pins Specialpin functions

.

Powersupplies

fomments for Teachers and StudentE While the targetaudiencefor this book is Grade 11 (junior) and Grade12 (senior)high schoolstudents preparingfor postsecondaryeducationin engineering,

computerscience,mathematics, or physicalsciences, it shouldbe appropriatefor universitystudentsor technical hobbyistslooking for more informationon programmingand interfacingPIC microcontrollersinto an application.To ensurethat the materialpresented herewould be relevantto high schoolstudents,the Ontario Ministry of Educationcurriculumguidelines for Computer Engineering(found at www.edu.govon .ca/eng/document/curricuUsecondary I gradeLLl2 /tech/tech.html#engineering) havebeenusedasa referencewhen topics,experiments, and materialswere selected. This book shouldbe usefulboth asa course text and asa referencefor both teachersand students. After working throughtheseexperiments, you will not only havea good understandingof how PIC16F684 and PIC12F675microcontrollers(and indeedthe entirePIC family of microcontrollers)are programmedand interfaceto other devices,but you will alsobe well on your way to beingcapableof creating your own sophisticated PIC MCU applications. Readingthroughthe experimentsin this book will not makeyou proficientin creatingyour own PIC MCU application.I am a firm believerin doing,and I would expectthat in any course,there would be many assignments that consistof modificationsof the experimentspresentedin this book.Theseassignments shouldgive studentsthe task of creatingtheir own applicationsand,aspart of the process, planning, wiring,and debuggingthem.For the studentsto becomereasonablyproficientin developingapplications,they shouldbe given10 to 20 applicationsas assignments over the courseof a term in order to familiarizethemselves with the MPLAB IDE software developmentenvironment,the PICkit, and the PIC MCU operation. Along with providinginformationon Microchip PIC microcontrollers(the PIC16F684in particular), electronicsinterfacingprogrammingin C, and assembler programrning, this book attemptsto developand engenderthe importantthinking and problem-solving skillsthat are expectedfrom a graduateengineer. Theseskillsincludethe ability to work independently, perform basictechnicalresearch,createa development plan,and effectivelysolveproblems.Along with being usefulin professionalcareers,theseskills are criticalto your success in collegeand university. The experimentsin this book do not lend themselveswell to group activities-you'll find that it is difficult to dividesmallmicrocontrollerapplicationsinto differenttasksthat can be carriedout by different membersof a group.For this reason,I recommend assignments that are limited asone-studentprojects. Projectsgivenduring the term shouldbe solvablein lessthan 100linesof code(two printed pages)and shouldnot requirea lot of researchon the part of the

lntroduction

...:

;: ,: :.:

student.Insteadtime shouldbe spenttrying to decide the bestway to solvethe programand structurethe software.All of theseprojects,exceptfor a summative project,sholJldbeeasilycompletedin a week or less.

.

H Noteto StudentE: .

.

.

Teachersare very good at figuring out when an assignmentis copied or plagiarized,and getting caughtwill land you and any other students who are involved in trouble.Copyingcodeor circuitry from the Internet or other books will be identified quickly asit is difficult to rework them to fit into your designsystemor style of programming.In any case,cheatingwill not help you gain the necessaryskills for developing your own application(and ultimately passing the course).In short,hand in only your own work and make sure that you can explainthe It will pay how and why of your assignments. off in the long term. spenda few When given an assignrnent, momentsa day on it, no matter what.Don't leaveit until the night before it's due.By doing a little bit of work on it eachday,your subconsciouswill work on the assignment,and when it comestime to finally createit and wdte it up, it will seema lot easier. Don't be afraid to try somethingdifferent.The worst thing that can happenis that it won't work-the upsideis you will discovera way of approachingthe problem that is very efficient and easyto implement.In this book, there are severalexampleswhere I just tried different things and discovereda better solution to a problem than I would haveexpected(and cases where the alternativesolution wasworsethan the original).

|-;

ff t:'"j

.i,"j

ful

H Noteto Teachers: .

;r1

'r{

ii; !r -r''i it-J

10

For teachersconsideringusingthis book asa I would like to emphasize text for their courses, that the materialis designedfor the PIC16F684, PICkit 1,and,to a lesserextent,the PICI2F675. I realizethat investmentshavebeenmadein other PIC (and other) MCUs, in programmers, in and other equipment,but the MPLAB IDE/PICC Lite compilerand PIC16F684/PICkit combinationis an extremelyflexible and costeffectivetool for applicationdevelopment.

.

Tiy to usereal-world situationsfor your assignmentsand try to vary them,both to interest your studentsand to make it harder for them to copy from preexistingmaterials.A good way to is to keep a comeup with theseassignments notebookhandy and record the different things you seein your travels.Toys'R Us, Radio Shack,TheSharperImage,and other retailers can be wonderful sourcesof inspiration. Lead by example.You shouldwork through as many different applicationsuntil you are comfortable doing so and can debugmost of the problemsyou experience.An important tool to be familiar with is the MPLAB IDE simulator. A coupleof teachershave told me that they don't bother with the simulator when they are teachingbecausestudentsprefer to seeflashing lights or somethinghappening.Pleasetry to break this habit and encouragethe use of the simulatorasa tool for verifying the operation of the codeaswell asfor debuggingexecution problems.Using the simulator will give students the ability to seethe program working or not working,and why it is not working before making the effort to wire the application.For virtually all applicationsthat run the first time power is applied,the developershould have demonstratedthe corrgct operation of codeon the simulatorbefore he or she attemDtsto burn it into a PIC MCU.

lcons and Conventions At the start of eachsectionand experiment,you will fild one or more iconsindicating the parts and tools you needto have availableto complete the experiment(s).I havechosento do this rather than providing one central list of parts required for all the experiments in thisbook.Thereasonfor doingthis is to helpyou efficiently plan for the section'sexperimentswithout having to buy many hundredsof dollars of parts (many of which you will not needfor months).I have tried to keep the number of parts to a reasonableminimum by designingasmany experimentsaspossibleto execute within the PICkit 1 starter kit-once the PIC MCU is programmed,the applicationprogrammedinto it can executeon the PICkit 1 starter kit without modification. The iconsusedto specifypartsand operationsare asfollows: At the start of eachsection,I will list the required partsfor the sectionunder this icon (seeFigure i-22).As I indicated,this is a summationof the parts usedin all the exoerimentsof the section.

l , e 3 P I C @l ' l C UE x p e ni m e n t s f o r

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Genius

F{ !!E

.t a.* !'r,

Figure i-ea

RequiredPartsicon

Figure i-eq

.l*

PICkit I starterkit icon

l ;

':i" i't, ..:}

Figure i-a3

PC/Simulatoricon

Figure i-45

PartsBin icon

Figure i-e6

Toolboxicon

Virtually all of the experimentswill requirea PC (indicatedby Figurei-23)runningWindowsand loadedwith rhe MPLAB IDE and PICC Lite compiler.ThisPC shouldbe runningone of the following versionsof Microsoft Windows: o . . e .

Windows98 SE WindowsME WindowsNT 4.0 SP6aWorkstations(NOT Servers) Windows2000SP2 WindowsXP

And the PC shouldhave32 MB memory (128MB recommended),95MB of hard disk space(1 GB recommended),CD-ROM drive,alongwith Internet Explorer 5.0or greaterwith an Internet connection for installationand online Help alongwith one free USB port. When the PICkit 1 starterkit icon (seeFigurei-24) appearsat the start of an experiment,it meansthat the PICkit is requiredeitherasa platform for the experiment or as a PIC MCU programrner. The PartsBin icon (seeFigurei-25) specifieswhich partsare requiredfor the application.Partsmay be reusedbetweenexperiments The lasticon (seeFigurei-26) liststhe tools requiredto createthe application'scircuit.Youshould not requireany specializedtoolsfor the experiments presentedin this book.Rememberto wearsafety equipmentwhendoingany cuttingor drilling.

In terms of conventionqI will use both StstemInternationale(Sl),better known asthe metric system,and English measurementstogether where possible.I recognize that there are still a number of issueswith specifying the correct measurementsystem,so by listing both I hopetherewill be lessconfusion.Standardelectrical prefixeswill be used,andI assumethe readeris familiar with them.They include the following: k for thousands M for millions m for thousandths p for millionths p for trillionths I restrain from speciffng part numbers except whenI believethat only one manufacturer'spart shouldbe used.Often,equivalentsto variouspartscan be found in surplusand generalelectronicsstoresat a very low cost. For the screenshotsshownin the book, I haveused MPLAB IDE version7.01.I know that after this book

lntroduction

11

goesto press,later and more capableversionsof MPLAB IDE will be available for download from Microchip'sweb site.www.microchip.com The MPLAB IDE functionspresentedin this book will not changefrom version to version (except for fixesto discoveredproblems),so despitesomecosmetic changesin appearance,their operation will not change.I recommend that you alwaysuse the latest versionavailablefrom the Microchipweb sitebecause if you haveproblems,the first recommendationthat you will be givenwill be to try againwith the latest version of the software.

FindingParts When you are first starting out in electronics,it can be difficult to find retailers to provide you with the parts and tools to createyour own circuits.Over time, you will developa network of storesthat havethe parts you need,but if you are startingout or are looking for better suppliers,here are somesuggestions: .

.

Along Mouser Electronics(www.mouser.com). with Microchip products,Mouser also hasan excellentselectionof opto-electronicparts. I find Radio Shack(www.radioshack.com). Radio Shackto have a number of components that I can't find anywhereelse(thermistors, TRIACs) aswell asgood-qualitywire at a reasonableprice.Recently,Radio Shackhas includedsomeMicrochip PIC MCU chipsand the ParallaxBASIC Stampto their catalog. Incal electronicsstores.InToronto,I recommend Supremetronic(www.supremetronic.com) asit hasall the passiveand discreteparts that I need,prototypingPCBs,and other usefulparts that are nice to handleand choosefrom instead of decipheringPDFSon line. Local surplusshops.If you are in the Toronto area,I'm sureyou will recognizeActive Surplus (www.activesurplus.com) by the large stuffed gorilla out front. While having a good selection of electronicparts,surplusstoresoften have a variety of other parts and subassemblies that are perlectfor hackingor designingnew controls.

Digi-Key (www.digikey.com).Ihavenot found a sourceof parts anywherein the world that matchesthe selection,price,and serviceof Digi-Key. Jameco(wwwjameco.com).Another excellent supplierthat carriesMicrochip parts.Also carries a good selectionof robot parts (including gearsand motors).

S*!

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L2

l,e3 PICo llCUExoeniments fon the Evil

6enius

Section

One

Underthe Eoversof the PlElEFEBq

1Plcl6F684

Before astronomersbeginto investigateand learn more about a star,they make surethey fully understandthe tools they are goingto use.Thetools to be usedare chosenfor their ability to investigatethe specific aspectsof the starthat is to be studied.Althoush a fewdiscoveries havebeenmadewith poorlyundelstoodequipment,the vastmajority of obseruations haveresultedin failure.Justlike astronomers, before we investigateand learn aboutthe MicrochipPICP microcontroller(the PIC16F684specifically), we want to know asmuch aspossibleaboutthe toolswe are goingto be using. The PICkitrM1 starterkit is an excellenttool for learningaboutthe PIC microcontrollerasit includes, alongwith its programmingcapability,a basictestcircuit that you can usewith a PIC MCU. As shownin Figure1-1,the PICkit starterkit providesfrom 8 up to 12individuallyaddressable LEDq alongwith a button input and a potentiometerfor variable-voltage inputs.

The builtin programmerinterfacesto the developmentPC via aUSB port, which is preferableto serial or parallelports.Overall,the PICkit 1 starterkit is almosta perfecttool for learninghow to programthe PIC MCU and interfaceto hardware. When I describedthe PICkit 1 starterkit asbeins almostperfect.it probablysetotf somealarmbellsin your head-this type of qualificationis normallyused to describethingslike a usedcar or a blind date.In this case,I am beingasliteral aspossible.The PICkit 1 starterkit is an extremelygoodproductand an excellent first tool (probablythe bestthat I know of) with which to leam to programand interfaceto the PIC MCU. The threepotentiallynegativeissuesI would like to bring to your attentionregardingthe PICkit 1 starterkit are actuallyquite minor and,to some extent,canbe exploitedto help you better understand how the PIC MCU works. The biggestissuethat will haveto be addressedin this book is the organizationof the PICkit 1 starter kit's LEDs. If you wereto follow the wiring of the eightLEDS and the four I/O pins they are connected to, you would noticethat only two of the pins canbe outputs(asshownin Figure1-2).And if all the I/O pins to which the LEDs are connected(RA5, RA4, RA2, and RA1) weremadeoutputs,you would have multiple LEDs lit if you make any of the I/O ports high.The solutionto this problemis to enableonly two pins asoutputsat a tirne (one high and one low). This allowseightindividuallyaddressedLEDs, but not an arbitrarynumberof LEDS to be on at any siventime.

--ri ., I I

Figure l-'f

EquivalentPICkit I starterkit circuit

13

=:-

--ri " I I

Fiqurel-e

PICkit I stqrterkit LED on

Arbitrary numbersof LEDs canbe turnedon by scanningthroughthe LEDs,just asa TV's electron beamscansacrossthe cathoderay tube,turning on phosphorsone at a time.Thistrick will be demonstratedlater in the book and will be usedto display eightbits of data at a giventime.The organizationof the eightLEDs (alongwith the button andpotentiometer)wasmadeto supporteight-and 14-pinparts in the PICkit 1 starterkit's socket.That organization and the choiceof pins (and how they are organizedon the PIC MCUSthat fit in the PICkir 1 starrerkit's socket)is actuallyquite inspired,asit leavesthe six pins of the 14-pinmicrocontroller'sPORTC available for other uses. The secondproblemis that it takesa few mouse clicksto turn off the power goingto the programmed

part.I seldomrememberto turn off the power,andI doubt you will either.Although the differentPIC microcontrollersare very robustdevicesfrom the elecyou shouldneverpull them trical overloadperspective, from a socketwhile power couldstill be appliedto someof thepins.Althoughlhe zeroinsertion forca (ZIF) socket,which I showyou how to installlater in the book, goesa long way in mitigatingthis problem, you shouldstill be cognizantthat you could potentially be damagingthe PIC16F684everytime you plug it into and unplugit liom the PICkit 1 starterkit while the Plckit is still connected. The final issueto be awareof is the potentialliability of the USB port usedto connectthe PICkit 1 starterkit to the developmentPC.Although most commercialand homePCshavebuilt-in USB ports and versionsof the MicrosoftWindowsoperatingsystem that canaccessthe PICkit 1 starterkit very simply, thereare a numberof PCsin educationaland institutional settingsthat do not havethe requiredports or software.Thereis no easyfix to this problemother than trying to find the fastest,biggest,and mostmodern memoryPC to be usedasa programmingstation. None of thesethreeissuesare major showstoppers -they are reallyjust speedbumps,and they canbe overcomef airly easily.

1-l/0 Pins Experiment

Arguably the mostimportantfeatureof the PIC MCU (I/O) pins.The 12 pins availis its setof inpttt/oLtlp&l ableto the applicationdeveloperallow the microcontroller to sensethe outsideworld and output in differentways.ThePIC16F684tI/O pins are capable of manydifferentfunctionsincludinganalogand difBut asI first startintroferent digitalsignalprocessing. ducingthe chip,I will treat the I/O pins assimple

T4

digitalI/O, capableof sensingor outputtingsimple binarysignals.Themore advancedfeatureswill be addressedlater in the book whenyou becomemore comfortablewith programmingand working with the PIC16F684. The basicPIC MCU digital I/O pin designis shown in Figure1-3.TheIR/S bit controlswhetheror not the pin can output the valuesavedin the PORZ bit. The term TRIS is an abbreviationofTii-State and referencesthe tri-statedriver that candrive the PIC MCU'S pin.When the TRIS bit is low (0), the valuein PORT is driven onto the pin, and the pin is saidtobe rn output mode.whentheTRlS bit is high (1),the PIC MCU pin state,and the data level at is held in a high-impedance the pin canbe read without beingaffectedby the contentsof the PORT bit.This is known asinput mode. RememberingwhichTRIS stateaccountsfor which modeis cuite easvto remember:ATRIS valueof 1

l , a 3 P I C o l ' l C l JE x p e r i m e n ts f o r

the EviI

6enius

CONFIG(INTIO & WDTDIS & PWRTEN & !,ICLRDIS IJNPROTECT \ & UNPROTECT & B O R D I S & I E S O D I S & F C M D I S ) ' int

o

co

&

j;

i,

nain( )

(5

{

o

o

PORTA = 0t C M c o N 0 = 7 r / / Turn off Comparatola A N S E I J = 0 r / / turn of,f, ADC T R I S A { = 0 r / / Make RA4/RA5 Outputs TRISAs = 0t == 1)

whil€(1

(

< 255, < I29,

f o r ( i = 0 r i f o r ( i = 0 ; i

Figirre 1-3 l/O pin

RAI = ri

puts the pin in input mode,and a TRIS valueof 0 puts the pin in output mode.TheTRIS bit valueapproximatesthe first letter of input or of output. By convention,you will seeI/O pins referredto usingthe format

//

tor

(i

RAA = li

Forev€r i.all // j1-1-1,

sinple

Delay

Loop

Si1np16 Delay

lroop

D O LED ON i j

RA{ = 0t

].oop

//

< 255r < 429,

i11) jaa),

//

D0 tED Of,f

= Ot i Ot j //

< 255, < L29,

i11) // jaL>,

Simple

Delay

loop

sinDle

Delay

r.oop

D0 LED On AEain

a,&*

wherethe ampersand(&) representsthe port, and the numbersign(#) representsthe port's pin. So PORTA, pin 4 is known asRA4.This shorthandcanbe a bit confusingbecauseit refersto both the pin and the PORT register.TheTRIS bits are usuallywdtten in the rormat TRIS&*

with & and # beingusedin the sameway asthey are in lhe PORT bil/pindefinilion.Thesenamingconventions are usedfor both C and assemblylanguageprogramming. When I first presentedyou with the cFlash.cin the Introduction,the mannerin which the LED was turned on and off is not easyto see.To help you see the operationof the I/O port and how it affectsthe PICkit 1 starterkit's D0 LED,I createdcPins.c, which turnson and off the LED usingthe PORT andTRIS bits more explicitly. *incluale - Exalnine /* cPiaa.c

Operation

This Progran is a moalificalion wiEh nore e:.plicit writea to bits. RAA - IJED Positive RA5 - IJED tilegativ€

conn€ction cona€ction

nvke Drealko 04.09.15

SectionOne

of

PIC MCU PinE

of -cE1a6h.cthe TRIS and PORT

(i (j

= 0i = oi

i i

TRISA4

= 7i

//

for for

// LED lrrrned out

< 255, i11) < L29, itL), EltlE RA4 irto

Off

f o r ( i = 0 r i < f o r ( j = 0 r j <

//

Eue to

255r r29i

rnput

RA4 Not

i11) // j!!, i

aA4 = Oi ll Reslole oliginaL TRISA4 = 0, // conditions | / / erillw ) // Enal cPins

!{oale Dfivirlg

sifirple

Culrent

Delay

].oop

op€ratingr

Before enteringthe "while (1 == 1)" statement,the codeputsthe RA4 and RA5 pinsin output mode (writesa 0 to them) afterclearingthem (settingall bits to zero).After the while staiement,the codedelaysfor a half secondand then loadsRA4 with a 1,which drivesor sourcescurrentfrom RA4, throughD0, and is laken in,or sinked., by RA5.The codethen waits anotherhalf secondbeforeloadingRA4 with a zero, tuming off D0.Thisshouldbe fairly easyto understand; currentflowsfrom RA4 throughD0 and into RA5. Next,the programwaitsanotherhalf secondbefore loadingRA4 with a zero,turningoff D0.After another half-seconddelay,RA4 is loadedwith a one,andD0 is tumed on again.After anotherdelay,the LED is rumed off by purtingRA4 into inpur mode (the PORT valueof RA4 doesnot change).With RA4 in input mode,no currentcanflow throughD0.After another delay,RA4 bit is put backinto outputmodewith the PORT bit beinglow so the LED will be off.At this point,the programrepeats.

Under the Covensof the PIClbFhAq

L5

This programis a very simpleexampleof how the PORT bits work.With the basicPICkit 1 starterkit circuit, only one LED canbe turned on at any one time, which givesyou an opportunityto try and decodethe schematicof the PICkit 1 starterkit and try to turn on Later differentLEDs or a seriesof LEDS in sequence. in the book,I will presentyou with codethat will do this.But for now you might want to try and modify

cPins.cto turn on other LEDS by putting RA4 and RA5 into input mode,and then selectingtwo other pins to put into output mode and turn on another LED.When you do this,just usethe explicitwritesto the PORT andTRIS bits that I do in cPins.candsave methodsfor controllingthe the more sophisticated LEDS for later.

Experiment2-Eonfi gurationtljord One way the variousPIC microcontrollersdiffer from the otherchipsout there is in their ability to havecertain operatingconfigurationparameterssetwhenthey powerup.The configurationparametersare specified by writing to a specialword in programmemory, known appropiately enoughasthe Configuration Word.When mostusersstartworking with the PIC MCU, understandinghow this word is configuredis ignoreduntil it is time to programa chip and testit in an application,at which point they try to figureout the correctvaluesfor the conligurationword, often getting an incorrectvalue.Most incorrectvalueswill causethe PIC MCU not to powerup or apparentlyresetitself everylew moments. To avoidthis problem,whenI presentedyou with the initial cFlash.cprogram,I includedthe properconfigurationword specificationin the program,which is automaticallyrecognizedby the PICkit 1 starterkit programmerand storedin the PIC MCU, so that it will powerup corectly without any interyentionlrom you. Settingthe configurationfusesmanuallyleavestoo much of an opportunityfor error. The configurationword specificationis the followin the ing statementand startswith two underscores leftmostcolumnof the sourcecode: & WDTDIS & PWRTEN & MCI.RDIS & -CONFIG(INTIO UIIPROTECT \ & BORDIS & IESODIS & FCIIDIS);

This statementenablesthe internaloscillatorof the disablesthe WatchdogTimer,the external PIC16F684, resetpin, the low-voltagedetectcircuitry,and the advancedclockingoptions.Along with this,codeprotectionis disabled,meaningthat the contentsof the chip canbe readout.Note that the parameterwords (calledlabels)havedifferentvaluesfor differentPIC MCUs,and differentPIC MCUs may havedifferent oarameterwordsall together.

16

Each of the parametersof the -CONFIG statement is ANDed togetherto form a valuethat is saved in the configurationword when the PIC MCU is programmed.Thisvaluecould be calculatedmanuallyby readingthe "SpecialFeaturesof the CPU" sectionof the PIC16F684datasheetand creatingthe correct14bit value,or you can take the valuesbuilt into the PICC LiterMcompileror MPASMTMassemblerinclude fileslistedin Table1-1andAND them togetherasI havedonein the previousstatement.ANDing together the includefile valuesforcesthe compileror assembler to calculatethe configurationword valuefor you,saving sometime and ensudngthat the valuesare correct. When specifyingthe valuesfor the configuration word,make surethat everybit of the configuration If a bit is forgotten,then chances word is represented. are the other valueswill make it a 1, which may or may not be the valuethat you want for the configuration word bit.To emphasizethe importanceof havingspecified a label for everyconfigurationword bit, I want to point out that trying to figure out why a PIC MCU won't run properlywhen a configurationword bit is misprogrammedis incrediblydifficult. As I will discusslater in the book, the PIC16F684 internalclock,negatingmuch of hasa high-accuracy the needfor an externalclock (althoughone can be added),the 1N71O,in the -CONFIG, specification enablesthis clock and savesyou from havingto add your own clockcircuitryThe other optionsthat I have selectedwere chosenbecausethey tend to make your life easierand alleviatethe needfor you to comeuP with any specialexternalcircuitry to the PIC microcontroller. you may As you work on your orm applications, experiment values and want to changesomeof these with configurationword options.Chancesare you will end up with a situationwherethe selectedoptionsput the PIC MCU into a statewhereit cannotrun properlv If you end up in this situation,rememberto

l , a 3 P I C o I I C l JE x p e n i m e n t s f o r

the EviI

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Table 1-1 Eonfiguration Fuse Parameter SFeciftcations utth Hffected Bit(sl Listed First Bk #

PICC LIte Label

MPBSM Fssembler Label

13-12 N/A

N/A

Unimplemented;Read as 1

11

FCMEN

_FCMEN_ON

Fail-Safe Clock Enabled

11

PCMDIS

_FCMEN_OFF

Fail-Safe Clock Disabled

10

IESOEN

_IESO-ON

InternallExtemal Switchover Mode Enabled

10

IESODIS

_IESO_OFF

InternallExtemal Switchover Mode Disabled

_BOD_ON

Brownout Detect/ResetEDabled

O9-O8 BOREN 09{8

BOREN_XSLP

BOD_NSLEEP

rr1 t/

u

Comments

tv

F" ly F*

Brownout DetecvReset Disabled in Sleep

09-08 SBOREN

_BOD_SBODEN

Brownout Detecr/ResetControl by SBOREN

09-08 BORDIS

_BOD_OFF

Brownout Detect/ResetDisabled

07

UNPROTECI

-CPD_OFF

EEPROM Data Memory Protect Disabled

07

CPD

_CPD_ON

EEPROM Data Memory Protect Enabled

06

Program Memory Protect Enabled

06

UNPROTECT _CP_OFF PROTECT -CP,ON

05

MCLREN

_MCLRE_ON

_MCLR Pin Function Active

05

MCLRDIS

_MCLRE_OFF

_MCLR Ptr Function Inactive/Pin is Input RA3

04

PWRTDIS

_PWRTE_OFF

70 ms Power Up Delay Timer Disabled

04

PWRTEN

_PWRTE_ON

70 ms PowerUp Delay Timer Enabled

03

WDTEN

;J

_WDT_ON

Enable WatchdogTimer

03

WDTDIS

!'tl

_WDT_OFF

DisableWatchdogTlmer

24

RCCLK

_EXTRC_OSC_CLKOUT I _EXTRC

RC Clock, RA5 Ctockout

24

RCIO

_EXTRC_OSC_NOCLKOUT I RC Clock, RA5 t/O pin _EXTRCIO

24

INTCLK

_INTRC_OSC_CLKOUT I _INTOSC

Intenal Oscillator, RA5 Ctockout

24

INTIO

_INTRC_OSC_NOCLKOUT I .INTOSCIO

Intemal Oscillator, RA4 VO pin

24

EC

_EC_OSC

Extemal Clock on RA5, RA4 I/O Pin

24

HS

_HS_OSC

High Speed (4-20 MHz) Crystal on RA4 & RA5

24

XT

_XTTOSC

Nominal Speed (1-4 MHz) Crystal on RA4 & RA5

24

LP

_LP_OSC

Low Speed (32 kHz-1 MHz) Crystal on RA4 & RA5

N) I

Program Memory Ptotect Disabled

n |J.

q

Ft

0, F.

o 5

{

o changethe configuration fusesback to the default value that I have listed here,and use for most of the experiments.Once retumed to this valuq you can

Section One

changeeachoption individuatly, trying to find the one that causedthe application to stop working.

Under the Covers of the pICItFhAr+

L7

H

lJ-

3-PlE MEUVariableMemorg,Flegisters, ExFeriment L,!

and ProgramMemorg

,:4,',

;.; i. .:l

*:.,,

,.: ..t

.'-t:i*

:.,: ...:

:r.;

,,a

In the introduction,I outlinedsorneof the differences betweena microcontroller(suchasthe PIC rnicrocontroller) and a PC,and I noted that one of the big differencesin the applicationcodewasthe needfor providingcodeto initializevariables.Another differenceis how the applicationcodeloadedinto a PC or a PIC microcontrollerand how it is organized.Inthis experiment,Iwill explainthesedifferences(andthe needfor them) andhelp you understandhow information is organizedin the PIC MCU and someof the issuesthat you mustbe awareof whenyou are programmingthe PIC16F684. When computerarchitecturesare presentedfor the fimt time,somethinglike Figure1-4is shown,which is the standardPrlnceton or von Neumannarchitecture, The importantfeatureof this architectureis that the memory spaceis a singleaddressarea for the program memory,variablememory,andstqckmemortes;the for theseapplicationfeaturesare presented addresses asbeing arbitrary and could be placed annvhere in this addressspace.An interestingsideeffectof this computer architecture is that an errant program could escapefrom the programmemoryarea,start executrng throughthe variablememory stackRAM, register areas,and treat the data asprogramstatements. When a programis built for loadinginto a target Princetoncomputersystem,the file that is loadedinto the computeris organizedto reflectthe memory organizationof the memoryspace.As shownin Table 1-2,the programfile is broken up into segments,each at a differentlocation,with a differentsize,andwith differentinformation.This is a simpleexample;large PC applicationscanhaveliterally dozensof different, code,variable,data,and stacksegmentswhereasa

microcontroller application often only requires only four (reset,code,data,and stack).The compilerand other applicationbuild tools are responsiblefor specifying and allocatingmemoryin the application.

Table 1-2 PrincetonComputerFrchitectureFlpplicationFile 5egmenl and Function Function Reset

Addressapplicationstartsexecutingat. Usuallya golo at the start ofthe applicationcode.

Code

Application code.Startingaddressand sizespecified.

Data

Variablespacefor application.Startingaddressand sizespecified.Initial valuesfor variables.

Stack

Programcounterand data stack.

The PIC MCU is designedto use the Ilarvard computer architecture(seeFigure1-5)in which the program memory and variable memory/register spacesare kept separatefrom eachother.Along with this,the programcounter'sstackis alsokept in a separate memoryspace.The advantageof this method dudng programexecutionis the ability of the processorto the fetch new instructionsto executewhile accessing Bad programscanstill exeprogrammemory/registers. cute,but at leastthey won't try to executedata as of this methodis a loss The disadvantage instructions. of flexibility in applicationorganization(i.e.,changing data or stacksegmentsizesto accommodatedifferent applications).

Memory SDace .*

t; t:

.x :>;

Data Processor and Register lnterface

!"j *: r1 .

X i.'i

Figure f-tl

r.8

Princetonarchitecture

Figure f-5

Harvard architecture

l , a 3 P I C @I I C U E x p e n i m e n t s f o n t h e E v i l

Genius

The programfiles loadedfor PIC MCU and other Harvard computersystemsare much simplerthan the filesloadedinto the Pdncetoncomputersystems. Theseare producedby the MPLAB IDE, end in the extension.hex,and are usuallyreferredto as,,hex files."A typicalPIC MCU hex file consistsof two or three segments, one for applicationcode(startingat the resetaddress),one for the configurationfuses,and an optional one for electricallyerasableprogrammable read-onlymemory(EEPROM) data.For the applicationspresentedin this book,the hex files will consist only of the codeandconfigurationfusesegments. Thereis no needfor definingdifferentareasin the memoryspace. This lastpoint is subtle,but extremelyimportant. Whenyotsdeclarea variablein a Princetoncomputer system,you are speciflng the label to be usedwith the variableaswell asreservinga spacein memoryfor the variable.When you are declarea variablein a Harvard computersystem(like the PIC MCU), you are simply specifyingthe label to be usedwith the variable;there is no need(or any mechanism)to reservespacefor the variable.This meansthat the locationfor variablesin a Haryard computersystemcan be chosenwith much lessrigor than in a Princetoncomputersystem,and the Harvard applicationcan still be expectedto run. The separatememoryareasalsomeanthat initial variablevaluescannotbe loadedinto the datasegmenL in the Harvard computersystemvariablesare initializedfrom programmemory.In termsof hex file space, you saveon the needfor a datasegment,but you do requiremore for the initializationspace.For microcontrollers,this is not an importantpoint becausein either computerarchitecture,variableswill haveto be initialzed by code,becausethe applicationsare not loaded []to memoryastheyarewirh a PC. Although I've probablygivenyou the perception that variables can be placed any.wherewilly-nilly in the PIC MCU, the truth is a bit more complex.As I work throughthe book,I will explainthe variablememory andregisterspacein more detail,but for now I just want to note that they sharethe samespaceand explaina bit about the functionof the registers. What I am casuallycallingthe registersin this experiment are refefied lo as the specialfunction registersby Microchip (and,similarly,what I am calling variablememoryis more properlycalledthefile registers),the specialfunctionregisters(SFRs)listedin Table1-3are usedto monitor the statusof program executionaswell asprovidean interfaceto the hardwareperipheralfunctionsof the PIC MCU. As you read throughthe book, the functionand addressingof theseregisterswill be explainedto you.

SectionOne

Table 1-3 PlEl6FEBqMicrocontroller5DeEialFunction Flegisters

! & !

&,!,

ta

Name

Flddress

INDF TMRO

0x00& 0x80 IndexDataRegister 0x01 TMRoValue

PCL

0x02& 0x82

Low 8 Bits of the ProgramCounter

STATUS

0x03 & 0x83

PIC MCU ProcessorStatus Register

FSR

0x04 & 0x84

PIC MCU Index Register

PORTA

0x05

PORTA I/O Pin Value

9.i

PORTC

0x07

PORTC I/O Pin Value

i.i

PCLATH

0x0A & 0x8A Upper 5 Bits ofthe Program Counter

INTCON

0x0B & 0x8B lnterrupt Control Register

PIR1

0x0C

PeripheralInterrupt Request Register

TMR1L

0x0E

Low Byte of TMR1 Value

Function

TMR1H

0x0F

High Byte of TMR1 Value

T1CON

0x10

TMR1 Control Register

TMR2

0x11

TMR2Value

TMR2CON 0x12

TMR2 Control Register

CCPR1L

0x13

Low Byte of CCP Register

CCPR1H

0x14

High Byte of CCP Register

ft\ $-*

1t'

I E*tl

".,.t-

PWM1CON 0x15

CCP PWM Control Register

ECCPAS

0x16

CCP Auto-ShutdownControl Registet

WDTCON

0x17

WatchdogTimer Control Register

CMCON0

0x18

ComparatorControl Register

CMCON1

0x19

ComparatorControl Register

ADRESH

0x1E

High Bits of ADC Result

ADCONo

0x1F

ADC Control Register

OPTION

va:*

gn

:x

iLJ

0x81

PIC OperationControl Register

TRISA

0x85

PORTA Data Direction Pins

TRISC

0x87

PORTC Data Direction Pins

PIE1

0x8C

Pe pheral Interupt Enable Register

PCON

0x8E

PowerControl Register

OSSCON

0x8F

OSCTUNE 0x90

L,i,

i1r F.t

OscillatorControl Register OsciilatorTLningRegister

ANSEL

0x91

ADC Pin Enable Register

PR2

0x92

TMR2 Period Register

WPUA

0x95

Weak Pull-Up Enable Register

IOCA

0x96

Interrupt on Port ChangeSelect Register

VRCON

0x99

ComparatorVref Control Register

EEDAT

0x9A

EEPROM Data Register

EEADR

0x9B

EEPROM AddressRegister

EECON1

0x9C

EEPROM Control Register

EECON2

0x9D

EEPROM Write EnableRegisrer

ADRESL

0x9E

Low Bits ofADC Result

ADCON1

0x9F

ADC Control Register

U n d e r t h e C o v e r s o f t h e P f C l t F b gq

tf': tii it;*.d

yt"

it fil

{r? 19

Exp e r im entU- S im u l a ti n g c F l a Eh .ci n MP L H BID E

The simulatorbuilt into the MPLAB IDE is probably the leastusedand understoodtool availableto you, which is unfortunatebecauseit is the mosteffective tool that you haveto find and debugproblems.The reasonswhy applicationsare nol simulatedis due to the perceivednotionsthat it is too muchwork and that the programis either very simpleor basedon simple changesto a working program.Old handswill cringe at theseexcusesand rememberhow they learnedthe hard way.PersonalIy,Ineverattemplto burn a programinto a PIC MCU without first simulatingit and makingsurethat it works properly.I alwaysdo this beforeseeingif it will work in the applicationcircuit; by simulatingit first you haveconfidencethat the programshouldrun. In this experiment,I will work throughthe basicsof settingup the simulatorfor an MPLAB IDE project.I havea few commentsregardinghow it shouldbe used but, for the mostpart,I recommendthat you useit for all the experimentsin this book. Someof the initial programming(C and assembler)experimentsare designedto work only in the simulator,but onceagain, you shouldsimulatethe experimentsthat accesshardwarebeforeburningthem so you canunderstandhow theywork and what they are expectedto do.As you gainexperiencewith the simulator,you shouldalso developpersonalstandardsfor displayingdataand what the simulatoris telling you in understanding order to find problemsand gainconfidencein your program. After you havecreateda projectand havebuilt the sourcecodeto ensurethere aren't any syntaxelrors (languageformattingerrors),you shouldenablethe "Select debuggerby clickingon "Debugger,"then "MPLAB Sim" asshownin Figure1-6. Tool,"and After enablingthe simulator,the simulatortoolbar (seeFigure1-7)will appear.The toolbar will allow you to do the following: . Run the simulatedprogramat full speed.On a 2.4 GHz Pentium runningWindowsXP,I find that 1 simulatedsecondexecutesin about 3 seconds,

.

Stop executionat any tirne.A breakpoint,which forcesthe applicationto stop at a specificlocation, can alsobe put in the applicationcodeasI will showpresently. Clicking'Animate" causesthe program to run relatively slowly,so you can watch the flow of the program.I find that this feature is bestused to illustratethe operationof basicoperating concepts. The program (subroutineor function) can be executedone step at a time by clicking |he Step In icon. If the operationof a subroutineor function is well understoodand felt to be correct or if it takesa long time to execute,clicking the S/ep Over icon will causethe simulator to execute the codein the subroutineor function at full speedand stop at the statementfollowing the call to the subroutineor function If you find yourselfin a subroutineor function that is going to executefor a while,you can StepOut of it. After clicking this icon, execution will run at full speed,stoppingat the instruction after the subroutineor function call statement. To restart the simulationfrom power up, click on the Reseticon.This icon will causethe simulated PIC MCU to return to power up conditions and resetthe StopwatchandStimulus functionsaswell.

'fo

setabreakpoifi (whichcausesexecutionto stop when it is encountered)in your program,double-click on the statementat which you wish the breakpointto be placed.Executionwill stopwhen the simulatoris runningor animatingan application,whena breakThe breakpoint'sstatementis not point is encountered. executedbut will executeif the Run.Animate,or one of the Stepiconsis clicked.Figure1-8showscFlash.c with threebreakpointsset and the execvtronrun arrow pointingto the first statementin the program. At this time,you may want to start up your cFlash project,enablethe simulator,and put breakpointsat the threelocationsI havein Figure1-8.Onceyou have donethis,click on the Reseticon and you'll seethat thereis no run arrow.If you click on one of the Stepiconsrepeatedly,the alrow won't appearand you may think that you havenot enabledthe simulator properly. If you click on the Run icon,the programwill stop and the run arrow will appearat the first breakpoint (at "PORTA : 0"). Before the C programstartEthere

l , e l P I C @l ' l C UE x p e r i m e n t s f o r

the EviI

6enius

D d k . , . i

'CIPlCCLrTE\Bll.{flCl a4' C E cfl.sh @, cF ash.c'-O'cF dsh lbf,Zg9 .O .O MA_AA ,t EFOB4 'CleLCO-rT€\all.dPlCt E€'-E cFllsh.lde,'C\vvitig\8to Eli Gei],s\Gd;\cl ash\cFt&h ob , O"cFtash cot -0..F 4i

(

s 0 0 7 0 s 0 0 3 1( s000s I

Figure l-6

{)

hef -O -MPI-IA -l6FdB1

bv!€

1) btres 5) byls !o!ar Bnd 0 RAlt

EnablingMPLAB simulator

is somecodethat setsup the executionenvironment and callsthe C program.Placinga breakpointat the first statementin the programand then clickingon the Run icon after resettingthe simulator,will provideyou with an applicationthat is readyto go from the first statement. Now would be a good time to start single-stepping throughthe program. When you get to thefor statements,you'll seethat the alrow doesn'tmove for eachclick of the Stepicons or evenseeminglyfor the Animate icons.Thesestatementsprovidea half-seconddelayfor the programyou canexecutethroughthem quickly and stop at the statementsafter them by clickingthe Run icon. To understandbetter how long an applicationis taking to execute,click "Debugger"and then,,Stopwatch"to displaythe Stopwatchwindow shownin Figure 1-9.Thiswindowwill showyou how many instructioncycleshaveexecutedand how long it would

5ection One

havetakenif you wereworking with a PIC microcontroller runningat 4 MHz (whichis the defaultexecution speedof the PIC16F684).The simulatedexecution speedcanbe changedby clickingon "Debugger"and then on "Settings;"this pop-upalsoallowsyou to changeother operatingparametersof the simulator. You canalsomonitor the valuesof resisten and variables in your programby addinga Wuchwinclow (seeFigure1-10).Toadd a register,selectit in the pulldown to the dght of 'Add SFR" and click on ,Add SFR;" to add a variable,selectthe oneyou want from the pull-downto the right of 'Add Symbol"and click on 'Add Symbol."For your initial programs,I recornmendthat you alwaysput in the I/O (TRIS and PORT) registersaswell asall the variablesin your program.When you are putting registersand variables into the Watchwindow,you may feel that the method in which they are displayedis suboptimal.Youcan changehow they are displayedby right-clickingon the

U n d e r t h e C o v er s o f t h e P I C l h F h A q

2L

l-,;;;;

l*

. '' ;

iir:

"Animate"

,,Run,, :

z1€

,*.* 91ri

"Pause/Stop" "StePln' i-1..*

Figure l-7

Simulatoractive

::d

Execution at Breakpoint (ArrowOver '8")

'irj

:

Breakpoints Set

t: '.r-i ? . ;:1:

:;;.t i.i

Figure l-B

22

Settingbreakpoints

l , a 3 P I C o I I C I JE x p e r i m e n t s f o r

the Evil

Genius

14 H tU L* 3*t

{u

t t

Slopwatch Window Active (46 Cycles)

?"t *, Figure l-9

Adding Stopwatch l 1

."{ ?";"{

C J

"Watch"Window

nr

1 d

L!4t 'd6 'r

sur**e . |

qdt rd6r

|

4

l.@f---Effi

'f Figure -10 Addine aWatchWindoh,

Section One

Under the Covers of the PICl,tFhAr+

23

r*C

Ddll

Select RegisterNari DisplayType Sizeand Other

al.t

vdPs1tAetodt !d@----

l

kl!b---l '*li;----:j rro&l:-.+

l

Parameters

41

lFlr,iiIb*l htrf

4

'GqJ f@l@-tr_-ffi t r o @

;;:i*,-.;;;'

'f Fiqure I -'f

L"t

'"t .S'r H

U'

*n{ IJJ

Changing Watchdata types

variable,selecting"Properties,"and then changingthe data format asshownin Figure1--11. With the informationI havepresentedhere,you can simulate most of the functions of the code written for the experimentsin this book.Right now,you can just monitor the operationof the code,but in a later experirnent,Iwill showyou how to setspecificinput and register stimulus,which will help you seehow your applicationruns under differentconditions. For now,you canchangeregistervaluesby doubleclicking on their value in the Watch window and putting in new valuesmanually.Addingstimulusto a simulatedprogramtakesa bit more work than the execution,breakpoint,stopwatch,and variabledisplay stepsI've shownhere,but it providesyou with a way to testyour applicationunder constantconditions,rather than dependingon rememberingto set certainvalues manually. One of the nice featuresof the MPLAB IDE simulator intedaceis that it is the sameasthe ICD 2 debuggerand ICE 2000emulatorinterfacesThis meansthat whenyou startworking with thesetools, thereshouldbe only a minimallearningcurvegoing from the simulator.The simulator features I've presentedhere are alsopresentin the debuggerand emu-

24

lator.Debuggersand emulatorsprovidehardware interfacesto the application circuit (actually replacing the PIC MCU in the circuit) that you can monitor, set breakpointsfor, and repeatover differentsectionsof code,justasyou would in the simulator. that At the start of this experiment,I suggested you usethe MPLAB IDE simulatorto test all the applicationcodein this book (and any that you encounter)beforeburningit into a PIC MCU. By doingso you will gainexperiencewith the simulator and learn to comeup with strategiesthat work bestfor you.Additionally,you can experimentwith placing your editing,watch,and stopwatchwindowson the MPLAB IDE desktopin positionsthat makethe most senseto you and that allow you to debugyour applications efficiently.

For Consideration When peoplestart investigatingMicrochip PIC microcontrollers for the first time, they are generally overwhelmedby the numberof differentpart numbers (microcontrollers with differentlealures)thatare

l , e 3 P I C @l ' l C l JE x o e r i m e n t s f o r

the EviI

6enius

available.As I write thiE there are over 250 active PIC MCU part numbersto choosefrom, not including packagingoptions.Most PIC MCUs are available with at least three different packages;eachpart number is available with two operating temperature mnges,and the older parts are availablein different voltage rangesThis means,whenall is told, there are about 2,000differentPIC MCUs and optionsto choosefrom. Over the next two pages,Iwould like to make your choice a bit simpler. There are six rnajor PIC MCU families to choose from as I have outlined in Table 1-4.The PIC16F684 that is featured in this book may seemlike one of the lower-end PIC MCUs, but it is actually a quite flexible memberof the mid-range. The low-end PIC MCU processorarchitecture is available on many of the entry-level parts.The processor is very similar to the mid-range architecture (which is usedin the PIC16F684)but doesnot havesome immediate instructions,doesnot support interrupt requestqcannotsupportlargeamountsof variable memory and doesnot have any advancedperipherals. The mid-rangePIC MCU architectureis the mostpopular architecture(andusedin the PIC16F684),asit supportsmoderateamountsof variablememory advancedperipherals,and interrupts.The PIC17 high-

end architecture is somewhatunique to this familv of microcontrollers althoughit doesiave somesimjLritiesto the low-endand mid-range.The PIC18architecture is really a supersetof the mid-range architecture and it offers a number of featuresthat allow it to accessmore program memory variable memory, and peripheral registersaswell asinstructions that will simplify and speedup traditional applications.Once you are comfortable with programming the mid-range chips and have worked through the experimentsin this book,you shouldn'thaveany problemslearninghow to program and working with the other PIC MCU architectures Most new usersand hobbyistslimit themselvesto the partslistedin Thble1-5.Thesedevicesare all easily programmedeitherby the PICkit 1 starterkir, PICSTART@Plus,ICD 2, or a homegrown programmer (of which there are many different designsavailable for dornload from the Internet). The Microchip ICD 2 is a debuggerinterface that givesyou many of the capabilities of an ln-circuit emulator (ICE) without the extremecostof an ICE. I want to make a few commentson eachof the deviceslistedin Table1-5.The PICSTART Plusis a developmentprogrammer produced by Microchip, which can be usedfor all PIC microcontroller Dart

Table1-4

Il::::!il llc yi::?:::,T1P,'-. l"'"iIi* PICMCU Pmcessor Familg FlrchleEture

Programmlng PtugEm Plgqrithms and ICD Memory Tgpe

PIC10

Low-End (12 Bit)

ICSP and ICD

PIC12

Low-End (12 Bit)

ICSP

PlC12

Memory Slze

Begt4er Size

lO Plns

Featues

Flash

256 to 512 instuctions

16 to 24 bytes

4

Comparator

EPROM (OTP)

512to\,0u instructions

25 to 41 bytes

6

Mid-Range(14 Bit) ICSP and ICD

EPROM (OTp) and Flash

512to2,048 mstructrons

25 to 128bytes

6

Compamtor and ADC, Advanced Timers

PIC14

Mid-Range(14Bit) ICSP

EPROM(OTP) 4096instructions 192bytes

20

Comparator andADC, Advanced Timefi

PIC16

Low-End (12 Bit)

EPROM (OTp) and Flash

512to 2,04a instructions

25 ro 73 bytes

121o20

PIC16

Mid-Range(14Bit) ICSP and someICD

EPROM (OTp) and Flash

512to8,192 instructions

72 to 368bytes

PIC17

"High-End" (16 Bit) Parallel

12 to 33136ADC,Se al to 52 for I/O, Advanced LCD Timerg LCD, USB

EPROM(OTP) 2k to 16k rnsrucnons

272to902bytes 33 to 66

PIC18

"PIC18" (16 bit)

Extemal Bus,Serial I/O, Advanced Timers

EPROM (OTp) and Flash

6,10to 4,096bytes 16to72

ADC,Serial I/qAdvanced Time$

Parallel,ICSP on FlashParts

ICSP and ICD

SectionBne

8k to 64k instructions

Under the Covers of

the PICIEFhAt+

25

qt \J

n

n $l !-.

p-

o

r-t 8' al F.

o t

numbers-in somecasesadaptersare requiredto proanotherPIC MCU part gramthe parts.In somecases, numberhasto be usedto implementthe ICD 2 function for a specificPIC MCU. Although the PICC Lite compileris either restrictedor not availableon some of the PIC MCUs listedin Table1-5,the full product supportseachof thesePIC MCUs and doesnot limit the programsizeor numberof variablesrequiredfor the application.Each of the listedPIC MCUs hasflash programmemory!which meansthat they canbe erased by the programmerbeforeburninga new application into them.All of the PIC MCUs exceptthe PIC16F54 havethe mid-rangeprocessorarchitecture.I included the PIC16F54becausemany earlyintroductorybooks and web sitesreferencethe PIC16C54.and the PIC16F54canbe usedin its placefor theseapplications.Another traditionalbeginner'spart is the PIC16F84A,but I would recommendthat you consider more advancedandfeature-richchiossuchasthe

more advancedchipshave PIC16F627Ainstead.These peripheral aswell asbuilt-in oscilfeatures additional for you to add oscillator the need lators,eliminating circuitryto your application. I chosethe PIC16F684for this book becauseit is a mid-rangearchitecturepart (14 bit), canbe programmedby the PICkit 1 starterkit, and hasICD 2 and PICC Lite compilersupport.This chip alsohasa built-in precisionoscillatorand is tolerant of a wide rangeof operatingvoltages.It alsohasa wide rangeof peripheralsthat make it appropriatefor usewith applicationslike robotics.Tosummarize,Ifeel the ratio PIC16F684givesthe bestcost-to-performance (whenthe PICkit 1 starterkit and PICC Lite compiler is includedin the decision)for a mid-rangepart that couldbe usedin a wide varietyof different applications and would be easyfor somebodylearningto work with the PIC microcontroller.

Table 1-5 FlecommendedFirst PIE MEIJs Pan Number

Numbs Df Plns

PIC16F675 6

PtugEm Memog

Va able Mem1rg

PeipheBls

and Debugqel

PICC Lite su1pott

1,024inslructions 64 bytes

ADC,Timers

PICkit 1 starterkit, PICSTART PIUS,ICD2

Yes

Comparator

Plckit 1 starterkir, PICSTART Plus,ICD 2

No

PIC16F630

12

1,024instructions 64 bytes

PICI6F6U4

12

2,048instructions

l2tl byles

ADC, Comparator, Timers

PICkit 1 starterkit, PICSTART Plus,ICD 2 Using PICI6F688

Yes (Limited Size)

PIC16F54

13

512instructions

25 bytes

None

PICSTART Plus

No

PIC16F84A 13

1,024instrlctions

68 bytes

None

PICSTART Plus

Yes

PICI6F627A 16

1,024instructions 224bytes

PICl6F87x

26

192to 22 to 33 4,096to 8,192instructions 368bytes

Comparator,Timers, PICSTART Plus,ICD 2 SerialI/O ADC,Timers, Seriall/O

l , P 3 P I C @f l C U E x o e r i m e n t s f o r

PICSTART Plus,ICD 2

the Evil

Yes (Limited) JustPICl6F87?A and Limited

Genius

Section

Two

Introductoru f Programming

1Prc16F584

I often seethe C programminglanguagedescribedas the UniversalAssemblyLanguageby peopletrying to put it down.Thisisn't a very fair characterization becauseC is an extremelyflexibleprogramminglanguagethat wasthe developmenttool of choicefor virtually everyoperatingsystemin usetoday,aswell as for a long list of successful businessapplicationsand games. Along with commoncomputerscienceapplications,C is usedto programmore artificial intelligence, computer-aided designsystems, aerospacecontrol systems,andsupercomputerapplicationsthan any other programminglanguage.DespiteacknowledgingC's widespreaduseandpopularity,detractorstend to focuson a few points. C is an incrediblyrich languagethat makesit suitablefor a wide varietyof differentapplications. This richnesscanbe a two-edgedsword;insteadof forcing everydeveloperinto following a commonprogram layout,C allowsa wide of programmingstyles.As I will discussat the end of this section,multiple C statementscan be combined,which canmake codeunreadableto eventhe mostexpertprogrammer.An acknowledgment of C's capabilityto be written into incomprehensible codeis the singlepoint of the yearly"InternationalObfuscatedC CodeContest" (www.us.ioccc.org/) in which the most confusingcode possibleis createdfor prizes. The richnessof the codeis often givenasa reason for why C is hard to learn.I regularlycontestthis with proponentsof BASIC,JAVA, and other programming languages. All theseprogramminglanguageshavea similarnumberof statementtypes,and I do not believe that any one hasadvanlages over anotherto make

programmingwith it more efficient.In termsof readability,poor codecanbe written in any language.Good programsare not the result of the languagedesigner; they are the resultof the programmerthinking about how to approacha problemand clearlyexpressingin their codewhat the programsare doing. Additionally,C is heavilydependenton pointerEa programmingconceptthat manypeoplefind difficult to work with, debug,and understand,especiallywhen readingother people'scode.I admit that I like working with pointers,but this is due to spendingmanyyears understandingwhat pointerscan do whenprogrammedin C and how they can be usedmost efficientlyfor most applications. In this book, I will introduceyou to the basicsof C pointersand try to emphasizeonly the thingsyou haveto know to work with the language. For most C applications, pointers are minimallyrequiredand are often quite transparent to the operationof the program. My major complaintaboutthe C programming languageis one that few peoplecommenton;in its ANSI standardform, C cannotaccessdata smaller than bytes.The versionof C usedin this book canread from and wdte to bits,but you will still requiresome very convolutedcodeto carry out somehardware interfacing. Despitetheseconcerns,C hasa numberof characteristicsthat make it well suitedfor usein this book andfor individuals learningaboutprogramming. Firstly,becausethe languageis over thirty yearsold, a plethoraof bookshasbeenwritten about learningand codingit. Secondly, it is actuallyquite easyto wdte efficientandreadablecodein C, and a good portion of

27

the text in this book is devotedto teachingyou to do just that. Lastly,I believeHT:Soft'sPICC LiterMcompiler is the besthighJeveldevelopmenttool available for the PIC16F684microcontroller,and I'm pleased that it canbe usedin this book to teachyou aboutthe PIC@microcontroller. PICC Lite compilerhasthree thingsgoingfor it that I feel are critical to its usein the book and for use by new users.First,it integratesextremelywell with MPLAB@IDE. As shownpreviously,PICC Lite compiler works not only with MPLAB IDE's basicoperations,but it producesthe necessary information neededby the MPLAB IDE simulator,MPLAB IDE debuggers, and ln-cCircuitemulators(ICEs) to allow source-code-level debugging.I feel this is criticalfor producing,testingand analyzingapplications. Second,PICC Lite compilerproducesvery efficient code.In Section12,I demonstratehow I would solvea numberof math problemsusingassemblylanguage programming.At the start of eachprogram,I have written out the operationof the programin C;you may

want to cut and pastethis examplecodeinto separate C source-code filesand seehow efficientmy assembler is to the codeproducedby PCC Lite. I would be surprisedif my codehad more than 10 percentfewer instructionsthan any application,and I wouldn't be surprisedif there are caseswherePICC Lite version createdcodewith fewerinstructionsthan I did. Finally,the priceof PICC Lite compilercannotbe beat.PICC Lite compileris not a crippledversionof the full productiit includesa1lthe capabilities, including codeoptimizationand simulator/debugger/emulator support,of the full product.Thisis an important point becausewith PICC Lite compilerintegratedinto MPLAB IDE, you havea developmentenvironment with capabilitiesthat would normally costwell over $1,000dollars.Thkentogether,the C programminglanguage,with applicationswritten with an eyetoward readabilityand efficiencyand implementedin the PICC Lite compiler,is the bestmethodof learning aboutthe PIC microcontroller,microcontrollerprogramming,and applicationdebugging.

Experiment 5-Variable Declaration Statements Declaringvariablesin PICC Lite compileris generally assimpleas: int

variableNamet

beforethe main statementof the application.This will createa 16-bitvariablewith the labelVariableName (or whatevervariablenameyou want) that canbe used anywherein your program.In this experiment,I would like to discussa few issuesregardingvariableand hardwareregisterdeclarationsto help you make surethat you cansuccessfully createapplicationseventhough you haveworked throughonly a few experirnentsin the book. VariableName is a label and canstart with any upper-or lowercaseletter or the underscorecharacter. After the startingcharacter,the restof the label canbe any letter,number,or underscorecharacter.Blank characterscannotbe usedin a label;if blanksare encountered, the compilerwill try to divide the character stringsto determinewhich of them are programming statements, directivegor defines.These character restrictionsare alsousedfor subroutineandfunction names, For standardvariables,two optionsexistthat you shouldbe awareol The first is the ability to initialize the variablewhenit is declared.By addingan equals signand a constantvalue,you can setyour variableto

28

a specificvaluefor the programwithout havingto add anotherline later in the code.To initializethe variable r to 47,you would simplykey in:

Another option that is availableto the declaration statementis the constke1'word,which convertsthe declaredvaluefrom a variableto a constant: conat

in!

xconstant

= 47t

In the declarationof xconstant,anytimethe label xConstantis encountered,the compilerreplacesit with the value47.By declaringxconstant asa constant,you canno longerwrite to it. For examplethe statement: xconstant

= 48t

will return an error. If you were to look at the pic16f684.hfile that was put on your hard file whenPICC Lite compilerwas installedin the \PICCLITE\nclude folder,you will see a numberof statementsthat look like: static

volalile

unsigneal

char

tMRlIJ

e 0x08,

Theseare hardwareregisterdeclarationsand involveadditionaloptionsthat you do not needto be

l , a l P I C @l ' l C UE x o e r i m e n t s f o n t h e E v i l

Genius

concernedwith, becauseHT-Soft hastakencareof declaringall the hardwareregistersin the PIC16F684 microcontrollerfor you. I want to saya few wordsaboutvariablenames. Pleasetry to make an effort to make them representative of what they are beingusedfor. I seemany studentscreateprogramswith variablenameslike Reg3 whenthe nameRemainderor PWMValueis much more representative of what the variableis usedfor in the application.Although I recognizethat the variable memoryis limited in the PIC MCU, pleasedo not feel you haveto useone variablefor multiple functions;try to useeachvariablefor one purpose.Usingthe same variablefor multiplepurposescan makewriting your programmore difficult and causeproblemswhen different functionschangea variablein waysthat screw up the operationof other areas.

One areathat alwaysgetsnew programmersconfusedis in the areaof counters.I recommendthat you usethe conventionalvariablenamesof i, j, k, and n. Thesevaluescameinto usewith Fortran,the first highlevelprogramminglanguage,and by usingthem for this functionconsistently, they are immediatelyunderstoodwhenreadingthe code.By namingvariables approp ately,you will find the tasksof trackinghow datais beingprocessedby the applicationand of debuggingthe codemuch easier. As I explainmore aboutthe C programminglanguageto you, I will expandthe variabledefinitionto includearrays,pointers,and local and globalvariables. For the time being,if you keepwith the simpleformat of the variabledeclarationthat I haveqivenyou here. vou will not haveanv Droblems.

ExFeriment6-C Data Tgpes The bit valueis not supportedby the C languagestandard,and I would recommendthat you do not useit for variables.I realizethat a singlebit is usefulforlag variablesrn aprogram,but becausethe bit is not availablein other C implementations, you will not be able

Table 2-1 PICELite ComEilerData Tgpes Dependingon your programmingexperience, the need to specifyvariabledata typesmight seemnew and somewhatominousto you.The restrictedvariable memoryavailableto you in the PIC microcontroller under the PICC Lite compilercanmake the decision on whatvaluesto specifyseemingly moreominous. Therereally is no needfor this apprehension;most variablescan be declaredusingthe lnt datatype wilhout problem. The data typesavailableto you are listedin Thble 2-1.For the mostpart,the data typesfollow Americon NationalStarul.ards lnslinrle(ANSI) standards, or what I call StandardC values,and are availablein C compilen for other processors.This allowsyou to import programsor partsof programs(usuallyreferredto as snippets)that havebeencreatedfor other applications, but you would like to useon the PIC microcontroller. Similarly,if you wereto comeup with somegoodprogramsor algorithms,this could be exportedto other systemsquite easily. Threedeviationsexistin the PICC Lite compiler data typesto ANSI C that I havemarkedin Table2-1.

Tqpe

Bit Size Comment5

bil

I

Booleanvalue-Note: Not a Standard C data type ASCII character/signed integer(-128to 127)

unsignedchar 8

Unsignedinleger (0 1()255)

short

Signedinteger(-32,7681o32,767)

16

unsignedshort 16

Unsignedinleger (0 to 65,536)

int

16

Signedinteger(-32,768 to 32,767). sameasshofi

unsigned int

16

UnsignediDteger(0 to 65,535);same as unsignedshort

long

32

Signedinteger(-2,147.483,648 to 2.14'7 ,483,64'7)

unsignedlong 32

Unsignedinteger(0 to 4,294.961.295)

float

Reat(0 to 1/-6.81(10r3);Assume 3 dig, its of accuracy/default floatingpoint modc;Note:Nota Stanldard C datatype

21

Real (0 to 1/ 6.81(10r3)r Assume6 digits of accuracy/specified usingPICL D32 compilationoption Note: ln StandardC, this is float, not double

5ection Tu-ro I n t n o d uc t o r y C P n o g r a m m i n g

29

to import the codedirectlyto other implementations of the C programminglanguage,and you may end up gettingin a bad habit of working with bit variables. Note that I do not make the samecomment for individual bits in a specialpurposeregister.Theregister bits are uniqueto the PIC MCU and,assuch,would not be involvedin a codeexportto anotherdevice. me float anddoubk (floating point) variabletypes are substantiallysmallerin their PICC Lite compiler forms than in their high-end processorforms.For the most practical applications,you will not seea differencebetweenhow they execute,but you may have issueswith very large numbers or numbers having many digitsof precision.

ut {! I

H-l

As I haveindicated,the C data typesare strongly typed,andwhen you are equatingvaluesbetween typeEyou may get a waming or an error from the compiler indicating that a type conversionis required. If the data is stored in a format compatible with the destination,the simplestway of resolvingthis is to use the type cast,which consistsof placing the desired data type in parenthesisbeforethe sourcevariable.For example,if the variables i and j were different tlpes but data couldbe passedbetweenthem,a simpletype cast.asshownhere.couldbe used: i

= (iTr'ee) j,

The experimentfor this applicationis quite simple; just a few linesof codedemonstratewhat happens with type conversion: ff4

*incluale - rave6tigate /* cTlDe.c PICC lJite cdE)iler

Dala

Type

in

operation

Tbie Program shosra the D€eal for variab].es wheu dlata iE tsransf€rretl.

TtrD€ Casling

ThiB plograln IDE Siltrrlator on1y.

unaler

nlrhe prealko 0{.09.15

is

tlesigrned

tso run

the

of

MPr.al

char float

it jt

main ( )

t i = 47t

)

j = i;

//

can vou Plac€

char

i = i,

//

can you Place

float

(1 == llr while // Enal cTtrp€

//

into

f,loat?

inEo

Loop Forever

When you compilethis application,you are goingto get the message: warningt000l C:\ Evil Genius \c!P!.De\cTtDe. iq)licit converEioa of float to inlege!

c 27

:

is tellingyou that the statement"i = j;" This message When this messagecomes involvesa data conversion. up,you haveto decidewhetheror not to resolveit by usinga typecastor by leavingthewarningasis Rememberthat the two datatypesstoredata in different ways(whichcanbe inferredfrom Table2-1);casting the float type to a char is a bad idea becausewith the type cast,the fkst byte of the float type couldbe passedto the char without beingmodified.In this case, you would leave it asis. For virtually all the applications in this book and for virtually all the PIC MCU applications that you will do on your own,you will only requirethe int data type. This 16-bitbit-variabledata type will handlea reasonably largerangeof valuesaswell aswork with ASCII characters.This data type is handled well natively in the PICC Lite compiler,but for long and floating-point datatypes,additionallibrarieswill haveto be addedto the final application.Theselibrariestake up quite a bit of spaceand can slow down the execution of the appliTo avoidthis spaceissueand cationsignificantly. reducedexecutionperformance,I recommendthat thesedata typesnot be usedunlessabsolutelynecessaryand the impactof their operationis well understood.Later in the book, I will give you a coupleof thoughtson how to simulatethe operationof these data t)?es using8- and 16-bitvadables.

t,,l tt!

'&&* 3C

30

char?

l , a 3 P I C @l l C U E x o e r i m e n t s f o n t h e E v i I

6enius

l-+1

Experiment 7-Constant Formatting .aJ & !{DTDIS & PWRTTN & IICIJRDIS & -CONFIG(INTIO T'NPROTECT \ & I'NPRC},IECT & BORDIS & IESODIS & FC!'DIS) t

iU i-

main( )

{ 't rt

PORTA = 0t CMCONo = 7i // Turn off Corq)arators ANSEIJ = 0r // Turn off JU,C TRISA - 0*49t // E':able PORTA IJED Oull>uts

When I introduceddeclaringvariables,I suggested stronglythat variablenamesshouldbe representative of what the data is usedfor, and if the variablesare usedfor commonfunctions(suchascounters),they shouldbe givenconventionalnames.Thispleais commonto manyprogrammingbooks,but what isn't all that comrnonis a pointer to speciq/ingconstants in the mostappropriatedatatype for the situation. The readabilityof a programcanbe enhancedor damagedby programformatting,by variablenames,or by comments.

Table 2-2 EonstantFormattingOFtionsand 5uggested Best UseE Constant Definition Fomat

Best Use

Decimal

##

Default Value

Hexadecimal

0x##

RegisterCounterValues

Binary

0bf#ffifrfrf Noncounrer RegislerValues '#' Human InterfaceValues

ASCII

while(l

== 1)

l'a-

Ijoop Forever

//

{ ( 0 = = ( P O R T A& ( 1 < < 3 ) ) ) PORTA = '3'// Tuln on Fou! LED8 eLse PORTA = 4r // Turn on Remaining Four if

//

) //

)

IJEDS

erihw Enal cconfu8e

Chancesare,you couldnot understandwhat cConfusedoesby just looking at it.You will probably haveto look at a schematicfor the PICkit 1 starterkit LEDs and applicationinput hardware.By makingfour changesto this prograrn(and turning it into cClear.c),I think you'll agreethat the functionand what is happeningis a lot easierto understand. *incluale - *cconfuse.cz /* ccLear.c a Deobfuscator

after

pasaing

!i, i:?

through

T]hia is lh€ same program as $cconfuse. c-, but with rrore appropriately chosen constant tlata values. nyk€ predlko 0{ . 11. 1s

1= i:-;;

Thereare four waysto specifycomments,asis listed in Thble2-2 alongwith the situationswherethey are bestused.In cconfuse.c,I havecreateda simpleapplicationthat usesdatain differentformats;beforeburning it into a PIC16F684and runningit in a PICkitrM1 starterkit, try to figure out what it does. *incluale - wri!€ /r ccoffus€.c to plcki! Ilaralware in a Confuaing Way This program Derforms function ia obfuscated t]lDes.

CONI,IC ( IIITIO & WDTDIS & PWRTEN & I{CLRDIS IJNPROTECT \ & I'IIPROTECT & BORDIS & IESODIS FCI'IDIS ) i

nain( )

{ PORTA = O' Cl.fCONo = 7; // \tr'r ofg Cornpalators ANSEIJ = 0t // I'urn off ADC TRISA = 0b001001i // EnabLe PORTA LED Outsputss

Interface

wr!ire(1

a simple task. but ils b!' poorly chosen dtata

== 1)

//

looD

Forever

t it

fiE'ke prealko 04.11.15

(0 == 8A3 ) PORTA = 0b010010t

//

Button Presseal, D4, D7 On

PORIA = 0b000100r

//

BI'rt.Eo'r Releaaeal, D5, D5 On

//

, l

5ection Tulo

& &

//

D0, D2,

D1,

D3,

eli'nw Enal cclear

I n t r o d u ct o r y

C Prognamming

31

Threeof the changeswereto convertthe TRISA andPORTA registerassignmentvaluesto binary from decimal,hex,andASCII. I think you will agreethat they wereeffectiveand helpedyou seewhat washappeningin the applicationand the output values.The fourth changewasto eliminatethe complextestof the RA3 (button input pin) and simplydo a bit compare. With the bit compare,you couldeasilylook at the PICkit 1 starterkit schematicand seethat RA3 is connectedto a pulled-uppushbutton. When decidingwhich constantformat to usein your program,you might want to follow theserules: .:t,13 .

$ .i.il

.

-i-,

Use decimalby default.For basicvariableand variablefunctions,decimalis probably most appropriateand easyto read. Use binary when you are working with a register that doesnot containcounterdata.An

.

exampleof this is loadingthe OPTION register with the value0b10011111. Use hexadecimalfor registercountingor result data,Comparinga counter'scurrent valuewith a hexadecimalconstantwould be most appropnate.

.

UseASCII data when human interfacesare involved.Thisincludestext messagingaswell as userinput.

.

Data sizesshouldbe appropriate.Use six bits for the two setsof six-bit PORT andTRIS registers.For other registers,useeight bits.

I think what I am trying to sayin this experimentis bestsummedup by the maxim:"There are 10typesof peoplein this world: thosethat understandbinaryand thosethat don'1."

it t

a::-i

Experiment 8- RssignmentStatements .rj r", il i: t_'j'

1l'-.€ .'].{

,t:; I

c;

If you are familiar with other highJevelprogramming languages, you are awareof the statementtype called the assignment statemezl, which is usedto storedata of a variableof a specified type.In thepreviousexperimentEI havedetaileddifferentdata typesaswell as how variablesare declared.In this experimentI will presenthow assignment statementsare written in C. The basicform for a C assignment statementis: ValldbleNam€

.:;".1

.... ill1.:

1::

= E <pressiont

The labelVariableNameis a variable.declaredas shownin the previousexperiment.The singleequals signindicatesthat the variableis goingto havea new variablevaluestoredin it. I point out the singleequals signbecausethe appearanceof two equalssignsis a logicoperator,asI will explainin a later experiment. The expressionis a data type value that is the same asVariableName. An expressioncanbe a constant,the contentsof a variableor a seriesof mathematicaloper-

32

ations.AlthoughC is somewhattolerantof assigning differentdatatypes,you shouldalwaystry to make surethat the expression's type is the sameasthe variable's,and if it isn't,make sureyou understandany potentialissues. An exampleof a potentialissuebetweendissimilar typesis savinga L6-bitvaluein an eight-bitvariable.In this case,the upper-eightbits will be discarded,which could be a good thing (you are providedwith a simple way of strippingout the most significantbits) or it couldbe bad (with data lost).To avoidthis problem,I tend to declareall variablesasint (16 bit). Finally,the assignmentstatement(and virtually all other statements)is endedwith a semicoloncharacter (;).The semicolonis usedby the compilerto indicate the end of the statement.Theonly statementswhere the semicolonis not requiredare the onesthat end in a right brace(l) character.Whenin doubt,put a semicolon at the end statement;evenif it is unnecessary, the compilerwill treat it asa null stutementand ignoreit. To demonstratethe differentforms of the assignmentstatement.IhavecreatedcAssign.c: *includle - A brief /t cAssign.c Stat€ments This Program Demonstrales Statements work in C.

l , e 3 P I C @l l C u E x o e r i m e n t s f o r

the EviI

l,ooh

at

Assignment

how AaEigrment

6enius

nJake prealko 0 4 . 0 9. 2 4

//

j = 23, //

irt

//

uditiaLized variabl€ D€claration valiabl€ DecLareil with Initial ( Initialization) value assisnment

nain( ) t \ri', aBsigned (or loaaleal The variable with) the conalanl value 47 "i,, aaEigneal contents rhe variable //

)

//

"i"

axud "j"

aasigneal

the

Ean6 va1ue.

complex,with their functionbeingconfusedwith the built-in assignment statements. Access(readand write) of PIC16F684'sregisters and I/O Pinsis accomplished usingstandardassignment statementssuchasthe onesdemonstratedin cAssign.c.Theregistergbits,and pins are all declared in pic16f684.inc, which is loadedin by pic.h.cl-ight.cis a simpleapplicationthat simplyturns on D0 on the PICkit 1 starterkit and illustrateshow registerscan be written to 8 bits at a time,just as8-bit variables(of type char).Indivrdualbits are readfrom andwritten to in exactlythe sameway. #incLude - Sinple c Program lo /r clisht.c on a PIC16F584 in the PICkit 1

End cAsaigTl

The filst assignment statementis the initialization of the variablej. Thereis no differencebetweeninitializing a variableat its declarationand assigninga value to it in the ffustline of a program.You may find that initializinga variableat declarationis easierto read, makingits functioneasierto understandin the program.Thenext two statementsare basicassignments of a constantvalueand a variablevalue,respectively. Thesestatementsare commonto other programming languagesand their operationshouldbe obvious. The last assignment statementis probablysomething that you haveneverseenbeforein BASIC or other beginnerprogramminglanguages; the valueof i is giventhe valueofj, which itself is beingloadedwith a new value.Thisis one of the many capabilitiesbuilt into C that canbe usedto both simplify application programmingand obfuscatethe functionof the applicationcode.This,lultiple assignment statemen1which hasmultipledeslinalions [or theexpression. is reasonably clear,but asI will showin the next experiment, multiple assignment statementscanbecomequite

aA4 - LED Poaitive a-45 - r,ED Negative

Turn

on an LED

Connection Connection

myke predlko 0{ . 11. 10

CONFIG(II\TIO & WUTDIS UNPROTECT \ & UNPROTECT FCTiIDIS ) ,

PWRTEN BORDIS

& IICI,RDIS & IESODIS

&

nain( )

(

CMCoN0 = 7; ANSEIT = 0r TRISA{ = 0r TRISAs = Oi

// // //

Tlrr| A\rrL rtake

off conpalators off ADC RA4/RA5 Oueputs

aA4 = 1r n-4,5 = 0t

//

'\ErL

on LED

//

hoop

vr{hile(l l

//

== !),

End cliqht

Experiment9 - Expressiong potentialexistsin the capabilitiesof the C expression statemenlthal canmakeyour programmingeasierand more efficient.Unfortunately,this potentialcomesat a cost:it's easyto createexpressions that do not execute asyou would expect,and are very hard to debug.In this experiment,alongwith looking at differenttypes of expressions that canbe usedin your applications, I will presentsomeof the potentialpitfalls you may have to navigatearound. In the previousexperiment,I really skippedover what an exnressionis.Thisis unfortunatebecausea lot of

Section Turo

To demonstratethe operationof C expressions, I cameup with cExpression.c, which examinesdifferent

Introductory C Prognamming

33

formatsfor expressions and data.As you readthrough the descriptionof this program,I suggestthat you load and singlestepthroughcExpression.c so you canbetter seethe points that I am making. *incluale /* cE.Dression.c

-

Look at

Thia Program tlenronstrates Dif,f,er€nt E apr€aaions that

E {pressions a variety of can be createal

ilr

C.

nyk€ Drealko 04.09.23 Haralware Notea: ThiB Program has be€n wlit.ten to the MPtAa IDE Simu!.ato! ONLY,

naitt(

run

in

)

{ // //

n3" \i"

i = j * 1 1 ,

//

Siq)le

i = j * 0 x 0 B t

//

!4r1tip1y

i j

{r,{

*;

= 3t = i;

+ 0b00001011,

i

= j

i

= r0,

j

= 4e /

i

= (i

i

= j

+ Ai

// // ll // //

itl

r.,,.:l

l

-

4t

i

= (j

= i

j = r / 5

//

i = i

while

bg a Hex value

uulriDLy value

by a Binaly

Same AB previous Eoicad Oralet of

// I/

6,

/

//

E
c@s,lex Arithmetic E q)reEsion Involvingl Two Ogeratsion8 anal !'otced. Oraler of Operatlon6

L = j - s % 7 = L2 - s % 7 = L2 - s

/t // //

E qr!€aEion ErqrleEEion

Load. i with ASCII $8,, change 'watscb,, winalow aliaplay Eoflnag Eo ASCII to verify lo.retif.y. Ba6ic Division

5) %7,

5 %7,

the the

AriEbmetsic

//

// // // t / i = l i - 5 1 % 7 // = lL2 - 5' % 7

-

iB fa

but ao Operations

(5 % 7 = s)

* 2t

//

BrbeaLleil

asEighment:

t 6\ * 2

(1 == a)t

//

IJooDrorev€r

i r ) //

E'rd cE.pteaaion

t::

...i

The first two statementsshouldbe pretty straightforward.Inthe firststalement. theexpression is a constantvalue(3) that is storedin the variablei. Next,the

34

contentsof i are the expressionand they are savedin j. Theseare assignment statements,just like the onesin the previousexperiment. The next threestatementshavethe sameexpressions( x 11).Thedifferencebetweenthem is the numberingsystem(radix) usedto expressthe constant4. This is a reviewof the C DataTypesexperimentin which I discussed how usingbasesother than 10makes it harderto immediatelyseewhat is happeningwith the code. In the assignment statementsfollowing the three j x 11 statementqI am applyingthe basicarithmetic operations(addition[+], subtraction[- ], multiplication [*], and divisionUl, alongwith the modulusoperator [%]. The modulusof two numbersis the remainderof the divisionoperation.In the next experiments,I will look at someof the other operatorsavailablein expressions The next statementhasan expressionthat you haveprobablyneverseenbefore;I am addingthe contentsof the variablej to the ASCII characterzero (whichis specifiedin singlequotesas '0').The valueof this expression(and the valuestored in i) is 51 decimal,or if you changethe Watchwindow displayformat for i to ASCII, you will discoverthat it is'3'.This may be a surprisingresult,but if you were to reviewa tableof the ASCII codes,you will seethat the numericand alphabeticcharactersare defined together;so if you haveone character'svalue,you can jump to anothercharactersimplyby addingor subtractingthe differencebetweenthem.This property of ASCII codesis usedin a numberof placesin the book to algorithmicallychangevaluesinsteadof relyingon decisionstructures to changelhem. "i : the C 5) % 7;" statementhaswhat is known as a compkx. expressioz:that is,multiple operations are performed within the statement.Looking at the first statement,it shouldseemobviousthat five is addedto the valueofj and the sumis found usingrnodulus7. Right after this statement,I haverepeatedit with parenthesisaroundthe "j - 5" expressionremoved. When the full expressionis evaluated,you will seethe result(storedin i) is differentthan in the previous expression. The reasonfor this difference is due to the order of operationsof the operatorsusedin thesestatements. The multiplicationand divisionoperatorshavea higherorder of operations,or what you could refer to asexecution priority, than addition and subtraction instructionshave.Even thoughthe additionoperatoris encounteredbeforethe modulusoperator,the modulus operatorexecutesfirst becauseit hasa higher order of operations. To avoidtheseproblems,you shouldenclosehigherpriority operationsin parenthesis(indicatingthat their contentsmustbe evaluated beforethey are usedfor other operations)to ensure

l , A 3 P I C o l l C l JE x p e r i m e n t s f o n t h e E v i l

6enius

they executebeforeother operatorsexecute.Asyou look throughthe codein this book,you will seethat I am in the habit of alwaysusingparenthesisto ensure expressions are evaluatedin the order l want them to. The final statementbeforethe "while (1 =: 1):" statementmay look like a syntaxerror or somekind of comparison,but it is an exampleof what I calleda multiple assignment statementin the previousexperiment.Neither is true;the expressionsavesthe intermediatecalculationof i./6in the variablej before completingthe evaluationand storingthe resultin the variablei. This ability to embedassignments within expressions can help you simplily your programs and/ormake them completelyunreadable. When you first start creatingyour own C programs,I recommend

that you do not try to combinestatementsasI have done here.But whenyou gain someconfidencethen you might want to look for opportunitiesto take advantageof this capability.Especiallylook in situations wberethe intermediatevalueof a calculationis neededelsewherein your application. With the five basicarithmeticoDeratorsand the a b i l i t yt o c r e a t ec a l c u l a t i o n wsi l h m u l t i p l eo p e r a t o r s . you havethe ability to developexpressions for the vastmajority of applicationsthat you are goingto be w o r k i n gw i t h .B e f o r eg o i n go n .t r y l o w r i t eyo u r o w n applicationlike cExpression. Testout differentexpressionswith the five operatorslistedaboveand with constantdata in decimal,binary,hexadecimal, andASCII Iormals.

Experiment I 0-Bitr-r.rise Operators

.

As well asbeingable to perform mathematical operationson the contentsof variables,the C programming languagehasa numberof operatorsthat allow you to perform Booleanarithmeticon the bit contents of variables.Theseoperatorsallow you to easily processbit information,but they mustnot be confusedwith the logicaloperatorsdescribedin the next expenment. The four basicbitwiseoperatorsare asfollows: .

.

.

& -bitwise AND. When two valuesare ANDed together,eachbit in the result is loaded with the AND value of the correspondingbits in the two values(serif both the bits are set). I bitwise (inclusive)OR. When two valuesare ORed together,eachbit in the result is loaded with the OR value of the correspondingbits in the two values(setif eitherbit is set). ^ -bitwise XOR. When two valuesare exclusivelyORed together,eachbit in the result is loadedwith the XOR value of the corresponding bits in the rwo values(set if only one of the two parameterbits is set).

SectionTuro

- -bitwise negation.Thisoperatorwill return the negatedor complementaryvalue for each bit of the singleinput parameter(invert each bit). This operatormust neverbe confusedwith the ! logicaloperator,which will be shownto invert the logicalvalue,not the bitwise value.

Using thesefour operators,standardbitwise Booleanarithmeticoperationscanbe performedon differentvalues,asI showin cBitwise.c. After compiling cBitwise.c,Isuggestthat you work throughthe code(includingmodifyingvalues)in the MPLAB IDE simulatorasmuch aspossibleuntil you fully understandthe operationswork.When you are doing this, you shoulddisplaythe variables(i, j, and k) asbinary valuesin the Watchwindow. *incl"ude - Bitwise /* cBitswise.c

C operatols

This Prograln Denonstlates how bitwis€ arithrnetic oD€latioas wolk in c. Note:

Display

the

valiable

values

as

Boolean

\Bina!y".

nyke predko 04.10.02

char

i,

j,

ki

//

use

8 Bit. variablea

nain( )

t

Introductony C Pnognamming

35

//

hilialize

values

& it

//

AND Values

togethe!

rr = i I i;

//

OR valueB

k = i ^ it

//

xoR values

together

k = -i;

//

wLvetE the

aits

j

= a37i

k = i

k = ( i * 2 ) - j + (1 << 71,

together

ll

in

"j"

rtix BirLat! opelacors vrith

// Alitlu[€tic =- 1)t while(1 //

l

End cBitwise

The operationof bitwiseoperatorsis very straigh! forward.Going throughthe examplecBitwiseexperiment in the MPLAB IDE simulator,you shouldsee the Booleanarithmeticoperationsclearlywhenyou displaythe variablesasbinary in the order i, j, k. The Watchwindowwill displaythe two parametervalues directly over the result,allowingyou to comparethe inputsand outputsto the logic gatesdirectly.As shown in the laststatement,bitwiseoperatorscanbe combined with arithmeticoperatorswithout any special considerations. Although the bitwiseoperatorsare straightforward, you canrun into somedifficult-to-debugsituations whenyou write to registersin a PIC MCU (or any other hardwaredevice).Toillustratewhat I mean,considerthe laststatementof cBitwiseand haveit load a port directly.For this example,assumethat the hardwaredeviceattachedto this port savesthe leastsignificantfour bits of the PORTA, and bit 7 of PORIA is connectedto a deyiceclock.When the clockis pulsed high (or strobed),the hardwaredevicesavesthe four data bits.Thestatementcould be: p o R T A= ( i

* 2) - j

+ (1 << 7)r

//

wrire Dara

from j, which hasbit 7 set).This is a dangerousassumption asyou do not know how the expressionis evaluatedby the compilerand whetheror not the destinationis usedfor storingtemporaryvalues. Becausethe operatorsoutsidethe parenthesisexecute on the sameorder of operations,you can assumethey executefrom left to dght. In this case,PORTA is loadedwith the productof i * 2, and then hasthe contentsofj subtractedtuomit with the valueof 0x0D5 beingtemporarilystoredin PORIA. Finally,128 (1 << 7) is addedto the valuein PORIA to clearbit 7.In this case,you will haveinadvertentlystrobedthe four bits of data into the deviceconnectedto PORIA (becausewhenj wassubtractedfrom i * 2, bit 7 wasset and the final add clearedit). You haveprobably strobedin an unwantedvalueaswell.Thistype of problemis extremelyhard to find and debug;simulating the applicationwill not revealthe problem,and you may needan oscilloscope to seebit 7 changing duringthe instruction'soperation. The fix to this potentialproblemis to usean intermediatevaluefor all complexexpressions that are goingto be loadedinto a hardwareport.This changes l h es i n g l es t a l e m e ni nt t ot h el w o t h a t y o uc a ns e e below: k = (i * 2) - j + (1 << 7)' ,,

X::n"::";":i..

PORTA = k,

As a generalrule,neverwrite the resultof a complex expressiondirectlyto a hardwareregisterwithout first storingit in a file-register-based variable.If you follow this rule,you will guaranteethat the valuebeing storedin the registeris exactlywhat you want with no potentiallyproblematicintermediatevalues. It will probablybe surprisingto you,but the operators normallyreservedfor conditionallogic are part of just asthe adthmeticand bitthe numericexpressions, wiseoperatorsdiscussed in the previoustwo experimentsare.This givesyou someuniqueopportunities for cleverprogrammingaswell asan opportunityfor errorsthat are very difficult to find and debug.

::"1::"-"'" and knowingthat it endsup as0x055fi'om the simulation of the program,you are comfortableknowingthat bit 7 of PORIA is neverloadedwith a high value (i.e.,

50

l , e l P I C o 1 1 ( UE x p e n i m e n t s f o n t h e E v i l

6enius

H

Experiment 11-LogicalExpressions

vt F'

in

04.o9.27

i-l r ) }J"

r."8

i n t i = 5 , tnt j = 10, int ElpvaLuet

E.DreaBion

//

value

!"{

rnain ( )

(

The logic operatorsavailableto you in C are listedin Table 2-3 and return numeric true or false values.It is important to remember that logic operatorc are different from bitwise operators asthey return essentially binary values(Tiue or False),wherethe bitwiseoperator returnsthe logic operationfor eachbit.

Expvalue

= i

== jt

E.pvalue

= i

l= jt

r'IhaE is the value Falae? // Value f,or Tru€?

E:.9va].ue E Dvalue

= i = i

> jt < it

// //

E.DvaIue

= (i

!= j)

&& (i > j),

E:.pvalue

= (i

t= i)

ll

//

E .DVaIu€ = 1 & & l , E:.DVaIu€ = i & &

*r H

vallue f,or Falae? vallu.o for Tru€?

(i > i)t

Table 2-3 Logic Operatorg Lagic Operator Operalion

f,or

//

Tru€ Tru€

//

What abouts ORing?

// //

r'rvetE *i" r,oglc value *i. logic DoltbLe ravelt value

//

LooD Eoreve!

If if

a

// value for trrue AND FalB€? // valu€ for Tru6 OR Fala€?

Both one

valuea

F

!= 0?

F.r. E.Dvalu€

A = = B Return Tiue if the two valuesare equal.

= t

ll

E
A != B

RetumTlue if the two valuesare different.

A > B

ReturnTrue ifthe first value is greaterthan the second.

A > = B Return True if the first value is equalto or greaterthan the second.

while(].

== 1)t

0t

t d

gj

P

Endl er,ogic

A
RetumTrue ifthe fi$t value is lessthan the second.

)

A<=B

RetumTrue if the first value is equalto or lessthan the second,

By steppingthrougheachstatementof this program, you will make a few conclusions:the first being that Ti.ueis given a value of 1, and Falsea value of 0. You will alsoseethat the first six assignments work you your exacllyas might expectbasedon experience (Although the with other programminglanguages. idea that the result of a comparisoncan be used asa numeric may be somewhatnovel.) The last five statementsprobably are surprising,but they do emphasizethe point that logic operators are similarto standardoperators:Nonzerovaluesare treatedasTiue,and the zero valuesare treatedas False.From thesefive statements,you should seethat the samerulesthat are appliedto logicalvalues(zero and one) are also applied to standardnumeric values. This shouldbe kept in the back of your mind,because it allows for someclever programming tricks suchas:

A && B ReturnTiue if both valuesare true (not equalto zero). A !l B

ReturnTiue if either value is hue.

!A

Return the invertedlogic level ofthe value.

The experiment'sprogram(clogic.c) teststhese arithmetic operators for two different values.This program should be run in single stepsthrough the MPLAB IDE simulator with the Watch window set up and ExpValue displayed.As you step through each C statement,you will seethe resultof the logic expression savedin ExpValue. *incluilo - Quantify /* clogic.c Thia Plograrn looks €rg)r€aaiotr vaLuea D?ofluceal by thdr. Thia proglam ainulator. lEike

Is

tq

at enil

to

Logic lhe lh€

E:.greEaior

Valu€B

aliffe!€nt logic valuea lhal ar€

be ua€al wilh

juat

//

i

F 0x123{

*

(i

> {)r

ll

i,f, li > 4) ia lh€D 1 relulneal

Tru€,

th€

D!€alko

Section Tr.r.ro I n t n o d u c t o r y C P r o g r a m m i n g

37

FI X rd

r-9 {D {0

{n

t-,..

which is equivalent to: i r ( j > 4 ) i = 0x123{ t els€

The advantageof this type of programmingtrick is its apparentelegance. Although the singleline looks like it is much simplerthan the full iflelsesolution,you might find that it usesa greaternumberof programming statementsand file registersand that it takes longerto executedue to the needto includethe multiply routine.Additionally,the lack of gotosor diversionsto differentstatementscouldresultin a statementthat hasa constantexecutiontime,which can be a significantadvantagein someapplications. And althoughit may not necessarily be more efficient, you shouldnote that its operationis not intuitively obvious,and you and otherswill probablynot understandwhat is happeningin the statementby simply looking at it. Statementslike this are interesting curiositiesthat shouldbe avoidedunlessthereis a tangible reasonrequiringtheir use. The pitfall that you canrun into with C logic operators is with the eq&akto (==) statement.Thedouble equalssignis a good solutionto the problemof differentiatingbetweenthe assignment equalsand the comparisonequals,but it doesnot take into accountthe conditioningof peoplewho work with other languages like BASIC, in which a singleequalssignin an i/or a whilestatementrndicatesa comparison.It is very easy to forget yourselfand put in a singleequalssignwhen two are requiredfor a comparison. If a singleequalssignis usedin an expressionlike

I am not beingfacetiousby suggesting that you neverusethe equalslogicaloperator.If you are comfortableprogrammingin BASIC or other programming languages that havea singleequalssignasa compadsonoperator,you will havea greatdealof difficulty with the doubleequalssignin your logical expressrons. Throughoutthe book, I discusshow you canmake your programsmore efficientby Iookingat different waysof solvingthe applicationrequirements.It is a bit of a fine line to walk becausesomefeaturesof the C programminglanguageallow you to usefewer keystrokesto solvea problem,but often at the costof programreadability.(The exampleat the end of this sectionillustratesthis very well.)What you shouldbe lookingfor are optimizationsthat do improvethe readabilityof the code,improveits efficiency,and reducethe total applicationsize. A greatexampleof how this is done can be illustrated by looking at the first C programyou were given(cFlash.c)and looking at what its basicrequirement is (i.e.,to togglethe LED at RA4/RA5 on and off). In the originalcodeI gaveyou,I explicitlyturned on and off the LED, but by thinking of the problem from anotherperspective, for example,that you want the LED to be toggled,you might think in termsof basicBooleanalgebraandconsiderchangingcFlash.c to somethinglike the following: *incluale /* cFlash 2.e - Sinple oa a Prc16E684 This Plograln 2.c" .

is

an optimizeal

aA4 - LED Positive RJA5 - LED Negative

insteadof the requireddoubleequalssign:

the programwill behavethe sameasif i wasalways equalto 47.Tomakemattersworse,if you put a breakpoint to checkthe valueof i after the comparison,it will seemlike the valueis always47.What makesthe error so hard to debugis that it /oofr right.To avoid this problem,generallytwo approaches can be used. The first is to make sureconstantvaluesare placedto the left of the comparison.If a constantis to the left of a singleequalssign,the compilerwill return an error statingthat it cannotwrite to a constantvalue. The secondsolutionwill seemmore drastic,but it is effective100percentof the time.Simplydo not perform an equalscomparison.Instead,the resultof a not equalscomparisonshouldbe NOTted asshownbelow in the expressionthat is equivalentto i : = 47: ! (i

38

C Program

!o

Flaah

version

of

an LED

"cFlaEh

connection Connection

nyke predko 04.ta.a2

-CONEIG(IICIIO I'NPROTECT \ FCMDIS) t

irrt

i,

& WDTDIS & TINPROTECT

& PUIRTEN & MCI,RDIS & BORDIS & IESODIS

j t

nain( )

{ PORTA = O; CI4CONo = 7r ANSEI, = O'

TRrsa4 = 0r TRISAs = O'

// //

//

Turn of,f, Cdparators lPurn off ADC Make ItA4/RA5 Outputs

!= 47)

l , a 3 P I C @l ' l C UE x o e n i m e n t s f o n t h e E v i I

6enius

& &

1)

].oop

//

Forever

{ (i

for

= 0t

i j

BA4 - A,A{ ^ f, ) // elihw ) // End cFlash

< 25s; i++) // < 729, j++\ i Toggle

//

Sfinple

500ns Delay

LED St'ale

2

The change in ihe code was to change the two RA4 assignment statementsto one in which RA4 is toggled (XORing a digital value with 1 will always invert, or

toggle,its state).Thisallowedme to eliminateone of the 500ms delayloops,thuseliminatingan opportunity for error (i.e.,keyingin the seconddelayloop properly),which resultedin a better than 36 percent decreasein final applicationsize.Along with thesetangible improvements, the readabilityof the programhas beenimprovedbecausethe cornmentafter the XORing of RA4 statesclearlywhat the statementis doing and it can be directlyrelatedto the basicoperationof the program.

Ex per im ent l2- C o n d i ti o n a lE x e c u ti o n

Usingthe lf Statement the operationof the braces,I modifiedcAssign.cto createcstatement,casfollows: #incluale - A quick /* cgtat€ment.c stat€ments in c This work

Prosran in c.

further

qrperiment

er.amines

legarding

hovr statenents

m]'ke preflko 04.10.05

The basic form of the if statement in C rsi if

($er€ssion)

//

Test t'o Be€ if.ErrDression" is Not zero \E>!I)r€ssion" if

!5 0 \'else,, else // Optional statement which Statement if E:{pression is // Executes

int int nairl(

(i

(j

/

3)

/

3))

followins // Execute | / if. "i / 3" is no! // //

slatenent zero

Execute f,ollowing ataternent it "j / 3" iB not zero.

In both casesthe next statementis executedif the resultofj dividedby threeis not zero.The secondcase is not that much more difficult to follow,and it avoids any issueswith comparisons with constants. As the if statementis written above,you might think that only onestatementcan be executedconditionally. This is not true becauseof the useof braces( {and}) to collectmultiplestatementsinto one.To demonstrate

Section Tuto

)

Zero \i" (or assisned // The variabl.e the constant value 47 // Loaaled with) Blaces B€ Put in before a slatement? // ca { "i" i = ir assisned conlents // The variable / / ot \jt . i = j = 1, // \\i,, and '.j,' aasigneal the Bame ll vatlte. , / | E'rd. of State$e[t i

!=

variable unilialized Declaration variabLe Declareal with hitial (Initialization) value assigrhent

ll // //

{

and is similarto the operationof the if statementin other structuredlanguages, althougha few points shouldbe noted.The first is that the test expression doesnot haveto be only a simplecomparison;it can consistof complexterms,which may or may not have comparisonoperatorsin it.The two expressions in the if statementsbelow are equivalent (0

it j = 23t

= 47i

while(l //

)

== 1),

Enal cstatement

Using braceschangesthe basicform factor of the if statementto: if

(Expres8iorr)

| // ope'ri'rg statelrentr Statelr€ntr gtatementt

'Expressionleet if is Not zeio Blaee to colLect stat€lr€nts statenents that // Multiple // Errecute if, E>(I)lession // i.s Not Zero // //

Introductory C Programming

39

if, E:<pr€asion is zero else // Execute Statem€nls { // Opening Brace to Col1€ct E.ecule Stalemeatr Statements lhal // Uulliple ia zero Slat€lrent r // E.preEaion Slatement t

I

//

if

fi

This is the recornmended format for peoplejust startingout programmingin C.The bracescan be eliminatedif thereis only one statementfollowing the il for example:

. r"*

if

(a == b)

to help keep track of what the program is doing. For simple programg it is hard to seethe importance of this trick, but asyou work with more complexapplications,the needwill becomeobvious.You'll find it necessarywhen the compiler comesback with the messagethat thereis eithera missingor an extra closing brace.This is a goodhabit to get into andwill later saveyou time and grief debuggingsyntaxerrorsin your program. To demonstratethe operationof the if statements,I createdthe cllc applicationasfollows: *includle

of

Oreration _,t

9 3

w 5' l>et-i

i-g't f'{

-l

",={

.r*

But to avoidproblemsrememberingwhetheror not bracescanbe used,you shouldalwaysput them in and then stopusingthem whenyou are more comfortable programmingin C. In the basicform of the if statement,you might havenoticedthat I indentedthe statementsthat executeconditionally(i.e.,on the valueof the expression). This is a common programming technique to visually indicatewhich statement'sexecutionis dependanton the higher-leveldecisionstructure.I indentby four spacesfor eachlevel simplybecausethis is what the MicrosoftVisualStudioeditor uses.and I am simolv following its example. When you look at other people'scode,you may see that the openingbracesare not at the start of the next line,they couldbe placedat the end of the previous line asshownin the following: if

(E qEession)

Statem€ntt stat€tnentr gtalementt

;

// //

Thia program 1f gtatement.

'r.-t

9,*

operalio[

th€

^=21, nain( )

{ (44 == f,

//

"i"

n = n + 1r

//

Inc!€lle|rt

if

equaLs a cotrstant

{

Nn/

if

$iz

== 44

] €lse

t

n = n - 1i //

Decretnent if

Not EquaLs

.ExDressioa"

((j

if

{

j

|

Brace to Eail ) // closins if, E:.plession is else // Execute { Statsem€nlt Stat.ementE tshat // Uuttiple stal€menlr ia zero // if Er.pleaaion Stalementt

= (i 1 311 == 7l

= j + 1, // fi

(k = 22) |t = n + 1i eLse a - a - 1i if

zelo Execute

while(].

The compilerreally doesn'tcareaboutthe position of the bracesThey can appearanywhereafter the if statement.(The is alsotrue of the closingbraces.)I recommendthe placementshownherebecauseit is very obviousvisuallywhetheror not the bracesare presentor missing. You haveprobablynoticedthe "fi" commentplaced after the lastclosingbraceof eachif statement.The reasonfor this comment is to remind me of the purposeof the closingbrace;whenyou havea very complex and long program,the reasonfor the closingbrace canbe forgottenor confused.I mark all programstatementsthat producea bracewith their lettersreversed

,

//

Erit

--

// // // 1),

hcrem€'lt

Nn/

Note that stateneat,

there Ia a aingle ao no bracea requireal.

if

Nk'

equala

22

ctg

When you simulatethis application,you should noticethat I didn't put in the bracesfor the lastif previously. statement. As I indicated theyaren'l absolutelynecessary, but they are a goodideawhen you are startingout. There is a mistake in this program that should have becomeevidentwhenyou simulatedit.The final if statement,if (k : 22),alwaysexecutesasif k is equal to 22.This seemsstrangeuntil you canseeexactlywhat is goingon. Remember,the singleequalssign(=) a/waysbehavesasan assignment, and a doubleequals signis requiredfor a comparison.If you changethis

*r..;

40

of

i = 4 4 i j = 0t

int int

| // ti

g-{

lhe

myk€ pr€alko 04.10.18

Te6t- if is ll // \loE zeio !firLli.Dl€ that Ex€cut€ Slatetnenls if E
dlemonslrateE

\if"

l , e 3 P I C @l ' l C UE x o e n i m e n t s f o n t h e E v i l

Genius

singleequalssignto a doubleone,you will find that the programnow works properly. The problemof incorrectlykeyingin one equals signinsteadof two is very commonwith new C programmers. To avoidthe problemyou can reorderyour programso that you neverrequire an equalscompari son.For example,the lastfour linesof the application could be changedto the following: if.

lk

!=

221

n = n + lt

//

Increment

\n/

if

\k'

equalE

22

out how your codeis supposedto work and then do the reverse.

t".i

Another strategyis to alwaysput constantsfirst asin: LE 122 -= k) n - n + 1i €lse tr = n - 1t

// //

Increments

sn'

Declement

if

if Not

\kz

equals

22

,.1

ri; **J

Equals

This is marginallybetter but doesn'tprotectyou in caseslike "if (a : b)," wherethe comparisonsare both variables.In sucha case,forgettingto put in the second equalssigncausesthe valueof onevariableto be assignedthe valueof another.

I don't highlyrecommendthis methodbecauseit involvesnegativelogic.Thatis,you mustfirst figure

i.; ,t! '.,{i :",'

F,-;r

t

Experiment13-Nested ConditionalStatements

I

A logicalsuggestionwould be to placethe secondif statement(alongwith the statementsthat executeconditionallywith it) within a set of bracesafter the first if. Thiswould look like:

11; !'ir)

t*i iat

i f ( i > j )

(

i f ( k < n )

(

Statsement(a)

//

Ex6cut6al

if

"i

> j"

and

\k

Executetl

if

"i

> j"

anil \k

< a/

) Somepeopleare born troublemakers. When I was16,I had to go to a two-hour defensivedriving course becauseI had too many pointsfor speeding.Everyone in this coursewasgivena Driver'sEducationMqnual with the basicrulesof the road.Severalminutesinto the course,somebodyput up his hand and notedthat if a policeofficerwasdirectingtrafficin a mannercontrary to a set of traffic lights,then you must follow the policeman'sdirections,and if a farmer herdinganimals wasdirectingtraffic in a mannercontraryto traffic lights,then you shouldfollow the farrner'sdirections. He then askedthe question:"So,what do you do if there is botlr a police officer and a farmer that are giving contrarydirectionsto the streetlight?"I'm bringing up this little storybecausein the previouse>.periment, I presentedthe idea that the next statementafter the if statement(or the following elsestatement)would be executed.Andwhen I presentedthis conceptto a setof high-schoolstudentqI wasquickly askedthe question, what happensif you havean if statementfollowing anotherif or elsestatement?

Section Tuto

else

{ // ,

s!at6m€nt(a) // fL

>= n/

fx

, // fr Another solutionis to noticethat there are only two areasin the codeabovethat executeconditionalstatements,and they couldbe accommodated by two if statements: > j)

if

((i

//

stat€ment(a)

(

) elae

if

(i

&& (k < n)) ttrecut€al

if

"i

> j"

and

*k

< n,,

Executeal

j.f

"i

> j"

and

\k

>= n/

r."i" *...!.

f*r 1{ it,

> j)

t //

a1

Statse$ent(E)

I // ti

{,'.l

This methodisn't bad,but couldbecomevery long if statementsare wdtten for both the if and the else.And, dependingon how the compilergeneratedthe code, this methodcould be very inefficientin termsof code sizeand executiontime.

1 i

I n t r o d uc t o r y C P n o g r a m m i n g

41

&{

i_ld

s)

s) 6

The generallyacceptedmethodof combiningconditional executionstatementslike this is to recognize that the if statement and the conditionally executing statement(s)following it are all one statementand can be nestedunderneaththe originalif statementasin the following:

k = ot

Execul€al

if

*i

ExecuEeal

if

"i

> j"

enal *k

< n"

{

# ",".d !s{

c.' L;

EJ lri

StalelBent fi| //

(a)

> j"

andL \h

>= nz

l els€

This PlogrEnl wif!. .tunp b€tsw€ea aliffelent alue to itiffelent coatlitiona. The LED values

*.s"*

((4 == k) && (0 == n))

if

{ PORTA = 0b000000100r TRISA = 0b011101011t

Path

//

3

k = - 2 i

) (4 == k)

e13€ if

{

poRTA = 0b000000100t // TRISA = 0b011111001t

PaEb 4

k = - 2 ,

) (

{

LEDE

PORTA = 0b000000100r TRISA = 0b011011011t

j,

PoRTA TRISA |

ll

//

& &

//

0b000010000, 0t011001U1,

//

Path

5

Ei

| // fi k = k + 2r

//

N€xt

Tin6,

co to

\e1a€/

e rihw Enal cNoNest

OnceI had the programworking,I removedthe redundantbracesand looked for placeswherethe multiple if statementscould be combined into something simpler.I cameup with the following cNest.c: *incLuale - Jurltr Betsween IEDg /* cNest.c

Inain ( )

rrilh

ifs

\rif" NeEt lhe various Ithl.6 Program rrill anal get statenenta of ocNoNeBt.c" !o lry ia eaaier to f,ollow. Drogram that

t

42

5

t

rt

PORTA = 0, C!4CONo = 7r // r'rr! .ANSEL = 0r // Turn

Path

else

]

k,

//

)

a!e:

-CONFIG ( INTIO & VIDITDIS & PWRAEN & !,ICLRDIS I'NPROTECT \ & I'NPROTECT & BORDTS & IESODIS FCUDIS) t

i,

(0 == n)

if

LED Anoale Cathoale DO NA{ RA5 Dl RA5 RA4I D2 RA4 RA2 D3 RA2 RA{ D{ A.E5 RA2 D5 RJA2 RAs D5 RJA2 RA1 D7 A:A1 RA2

int

UJ

IJaEb 2

K != 0

//

t

|

-,i

Ilat }l L

) elae

ifa

lErhe D!6alko 04.11.15

d

k)

elae

iiJ

6""*

< L29t j++)l

PORTA = 0b0001000OO, // TRISA = 0b011001111, , // f,i

I shouldpoint out that this methodof nestingdoes not apply only to the if statement.It appliesalsoto all the conditionalexecutionstatementsin the C programminglanguage. As you work throughthe book, you will seemany examplesof nestedprogramming statementsof differenttypes.Actually you'veseenone already,the 500ms delaycodethat wasusedin the cFlash.cprogramconsistsof a for statementnestedas part of anotherfor statement. To demonstratehow nesting can simplify a program,I createdcNoNest.c.This programflashesdifferent LEDS on the PICkit 1 starterkit in a somewhat randomorder,but it is hard to follow and seeimmediately what is happening in the application:

r 1

! !

j

{

*incluale - aluJnlr B€tsw€e! LEDE with /* cNoNesl.c

&5F S.-{

= 0r

PORTA = 0b0000100OOi // TRISA = 0b011101011t

(

.ii"[

Foreve!

(0 == n)

if

slat€nenl(a) elae

w

Loop

valueE

{

) *-{

(j (0 --

if

{

//

//

tests

special

for (t = 0r i < 255t i++) // siry)te Delay rJoop for

a E ( r > t , i f , ( k < a )

//

== 1)

whl.1e(1

t

k & n ale

//

off conl)alators of,f, ,rDc

l , e 3 P I C @l l C l JE x o e r i m e n t s f o n t h e E v i I

6enius

a

The r,ED valuea

ar€!

eLse

LED Anoate Catboale DO RA{ RAs Dl RAs RA1I D2 RA4 RA2 D3 NA2 RA{ D{ NAs RA2 D5 AJA2 RAs D5 RA2 RA1 D? RA1 A:A2

if,

((4

== k)

&& (0 == o.l ) // Cdlbitr€ the ,/ Teat Coaalitions

PORTA = 0b0000001OO, ll TRISA = 0b0U101011,

Patjr 3

r1\

k = - 2 t

) elEe

{

rvk€ Dledlko 0{.11.15

if

F.(

(4 == k)

PORTA= 0b0000001OO, // TRISA = 0b011u1001t

Nr"

PaE}r 4

k = - 2 , , /t fr elae Lf (0 == n)

t

& P!{RTEN & !,ICIJRDIS & _CONFIC ( INTIO & lfIllDIS T'I{PROTECIII \ & IJNPROIECT & BORDIS & IESODIS & FCMDIS ) t

til

X rd

,

;J ;

PORTA= 0b000000100r // TRISA = 0b011011011,

Patsh 5

) elEe

inr nain(

{

j,

i,

k,

PORIA = 0b000010000r TRISA = 0b011001111t

nt

b.E>

5

)

I

{ PORTI = 0t CfiCONo = 7r // 'l''rt AIISEL = 0r // Tura

k = la L 2? //

while(l

k & n ale

-=

1)

//

SD€cial

Test

ve].ues

(1. = 0r (J = 0r

i j

Loop For€ver

< 255, < L29,

i11) jLLlt

//

Sirqlle

Delay

IrooD

(0 == k) (0 == n)

t PORTA TRISA -

Tine,

co

tso *e].se/

{'d

0b000010000r 0tr011101011,

//

Path

1

) elEe

t

PoRTA= 0b00010000O, /l TRrsA = 0b011001111t I ll fr

PaE}r 2

elihlr Enal cN€st

// //

)

t for f,or

N€xt

off CdEaratola off ADC )

k = O, //

g *

fr

ll

I

if if

Path

//

I admit that cNest.cisn't a hugeimprovementto cNoNest.cin tems of readability,but by reducingthe number of unneededbraces,I did manageto reduce the amountof spacethe main loop of the application takesandmadeit easierto look throughthe ent e application.This is an example of what you will seeif your taskis to supportan applicationthat hasbeenin usefor a long time and hasbeenmodifiedto reflect new requirementsand fixesto variousproblemsthat havebeenencountered.In thesetypesof applicationq it is often impossibleto understandexactlyhow the codeis working,and you end up makingsmallchanges that perpetuateits increasingcomplexity.

m ?-' I J ;t

tlt a

(tl f'r'

ExFerimentltl-The 5ulitch DecisionStatement

L

singlevariablemustbe tested.Multiple if and else statementscanbe combinedto meet the reouirements quite simply.Thecodebelowdemonstratesihis: (4 == L') ll

Go south

If

raalex et

'

'J

m

rr

{

&,

t Dir€ction

l

= 180,

' ela€

if

15 == L,

//

Go North

ll

co East

if

Intt€x

at

a 5 o ,",{

5

{ Dir€ctioD

Casesexistwheremultiple statementsare required becauseof multiple constantvaluesagainstwhich a

= 0t

) e].e€

if,

(7 == l,

if,

rDtlex

a!

7

t

5ectionTuuo I n t r o d u c t o r y C P n o g r a m m i n g

43

= 90t

Dilection

if

else

//

Go Iqeat

for

€Ise

€verylhinq

// //

t

n!

s

.t-,'

f,f) b.{ j't

I

= 270t

Directlon ll f!

If you were writing your application in BASIC, you statementslike the would probably use the seLect/case switch/casestatemenrsusedin cswitch.c listed below: *incLual€ - Detlonstrat€ /* cswlEch.c fhl,s Drogram alemonstratea awiEch atatdlent.

cE)eratLon

of

tsh€ op€ralion

ttsltilch" of

lbe

rq.ke prealho 0{.10.18

f 5

i n t i = { t int Di!€ction

= -1t

{t I

nain( )

{ switcb

(i)

t caBe 4. // Dir€clion bzaaki // c aBe 5t // Directioa bieaki case 7 . I / Dilection b!€aki default: // Direction ) // hcti\ta

rtr *-r ".{

{i!

!thil€(1

cio South lf = 180t r.eave switch if Go Norlh = 0t Glo Eaat = 90; co west = 2?0t

if

Ind€x

== 4

at

Even

; il

//

Slatem€ut the \Case/ Ncase Slatern€nt

the

Cour1tet

caae

7"gO / /

Goiug

aouth

Inalex

= {

caee

O .

Goirg

Norlb

Itral€t

= 3

Going

EaBt

Itrale*

= 2

Gol.ag Weat

IEdl€x

= 1

7 //

thlng

E1a€

ceee 9Or ll j - j + 1 , b!eaki tt€fault: //

== 1)t //

hcliws

E^d. crf

Obviously,you have to plan for situations where you can eliminate the break statementin your switch code,but whenyou do,you reallyhavea feelingof accomplishment-andthere'sa goodchanceyou've simplified the amount of application code required for the program.Wh€n you are startingout,you will probably use the switch/casestatementsfor situations like this one,where multiple if statementsexist, and all of them are comparing to a constantvalue and executing a break statementat the end of the case.

ai) ii{ ( a

r!1 ld54

}{{

Ls$ 44

!o

(

This application provides the samefunction of respondingto multiple possibleconditionsthat are listedin the multiple if statementsat the start of this experiment.By usingthe switchstatement,the codeis actually a lot simpler.The casestatement'sparameter combinedwith the switchstatement'sparameterforms the if statement:

"ir-' i-i

cas€Pafameler)

Di!€ctLoa // Clear (Dir€ctioD)

j = J + 1,

fo!

after nd{t

=-

The useof the casestatementis obviouslya lot easier to key and a lot lesslikely to havea syntaxerror like you had with the if statement. The "default:" conditionworks exactlythe sameas the elsestatementin the if statement;the statements after it executeonly if all parametersdon't match any of the casestatements. This is all there is to the switch/casestatements except for one point: the break statemetu.This statement causesexecution to jump out of the current switch statement and executethe statement following it. You can do someinterestingthingsif the break statement inside a switch block is not included. For example,if the switch block was being usedto record the direction of motion (keeping in the tradition of the wheel direction), it could increment the counter for each90 degreesrather than placing a hard value in the countervariable.The examplecodefor this implementation is: I = 0t awitch

stat€$eat Iaal€x aE 5

halex

Slaternentss sb!€ak" or \ // fL

] |

(SwitchPalameter

t

)

al

l , e 3 P I C @I ' l C UE x o e r i m e n t s f o n t h e E v i I

6enius

ir* i

E x per im entl5-fo n d i ti o n a l L o o p i n g

ili ,,?{

#ineLutle /* cFlaah !'lhile.c I.ED on a PIC16E584

ginE)le

to

Elash

an a-ii

|!hi€ Program is a noalif,ietl to uae ..whil€,' Loops iDsleaal of \fo!', loops RA4 - r,ED poailive ItA5 - IJED Negative

ti:: c Program

version

of

\tcFlash.c,,

:,- "

Connecti,on

i:

I'ke pretlko 0{.05.19

There are a coupleof rnethodsof implementingconditional loops.In this experimentI will look at the most common method: the bastcwhile loop. The while loop allowsyou to repeatedlyexecutea set of instructions while a test expressionis true.That is,the while loop canbe usedfor conditionallyrepeatingcode.But it can alsobe usedto implementinfinite loopsin your applications.Someprogrammingphilosophiesdo not use the basicwhile loop,but they alsodo not provideyou with the simplereadabilityof the basicwhile loop. The while loop is a programmingconstructthat testsan expressionbeforeallowingexecutionto take placewithin the loop.If the expressionis not zero,then executionwill take placewithin the while loop,and at the end of the loop,executionwill return to the expressiontest and the processwill repeat.If the expression evaluatesto zero,then executionwill skip pastthe loop andcontinueat the statementafter it. To showhow this works,the following statements canbe used:

while

(i

i

F nain( )

{

t\

PORTA = 0t CMCONo = 7t ANSEI = 0t TRISA4 = 0t TRISAs = 0t

ll // //

\E oft Corparatora Tuln of,f ADC !,take RA4./RAs OutDutg

//

Loop

l'i

it-,,'

while(1

== 1)

Foiever

!-:.

t i = 0, j = 0, whil€ ( (i

{ 1

(

a; < 2s5) ll

= t + 1t (i > 2s5)

//

(j

< 78))

Incronent

//

Ro11 Ov€!

//

ToggLe

ar!

S!fiaLL Counte! to

Larg€

i-J

Counler

J = j + 1, // fi ) // elihw

< {)

= i + 1; // elih!,r

& &

,

{ )

-CONFTG ( INTIO & WDTDIS & PWRTEN & MCLRDIS IJNPROTECT \ & T'NPRoIECT & BORDIS & IESODIS ECMDIS ) t

//

WhiL€

lJoop Coale

In thesestatements, the variablei is initializedto zero.Next,it is comparedto 4, and if it is lessthan 4 (i.e.,the expressionis true or returnsa nonzerovalue), the codeinsidethe while loop (incrementingthe variablei) is executed.Wheni is no longerlessthan 4, the while expressionbecomesfalse(and returnsa zero value),the codeinsidethe while loop is skippedover, and executioncontinuesat the statementafter the closingbraceof the while loop. To demonstratethe operationof the while statement in an application,I havemodifiedcFlash.cinto cFlashWhile.cin which the two for statement delays havebeenreplacedwith a singlewhile loop that incrementsthe two variablesi andj until they are both greaterthan 255and78,respectively:

5ection Tulo

R:A{ = RA4 ^ 1, | // eLihw , // wrd. cFlaah

LED

;-i

while

Although cFlashWhile.cis a direct copy of cFlash.c, I found if I usedthe sametestvaluesfor i andj (255 and 129,respectively), the delaywould increaseto 833 msecsrather than the standardvalueof 500ms By runningcFlashWhile.cin the MPLAB IDE simulator, I wasableto empiricallydeterminethe valuefor j that would resultin an approximately500ms delay. As you work throughthe code,you will discover that I usethe while statement while

(1 == 1)

a /ot.This is my loop-forevercode,and I useit either as the overallloop in an application(like this one) to

I n t n o d uc t o n y C P r o g r a m m i n g

45

l-,

the I/O and processingcode,or I placeit at encompass the end of the applicationto stopit from returningto the caller(and end up executingagainrepeatedly).The statementcouldbe simplifiedto: while

(1)

The PICC Lite compilercan detectstatementslike this wherethe test expressionis alwaystrue (or 1) and replacethe statementwith somethinglike:

| / / goto

insiale

Code Ex€cuteal IJooPt

vthile

loop

There is anotherform of the while loop.It is the do/while,which takesthe followingformat: alo t // Coale Ex€cutetl inside

) while

(orDreasion)

the alo/whil"e loop

t

This is a subtlemodificationof the original,whereduring the first time throughthe loop,the expressionis lo execute not lesledto be true;you areguaranteed the codeinsidethe loop at leastonce.The advantageof usingthis form of the while loop is that variablesor hardwareregistervaluesthat are testedin the while exoressiondo not haveto be initializedto force execution to work throughthe codeat leastonce.SomeC I implementationsh avethe do/untilstatement,whrch do not like becauseit forcesnegativelogic into your program(i.e.,loopinguntil a conditionis true is the logicalnegativeof loopingwhile a conditionis true). Two keywordsare alsousedin while loops:break and continue."Break" will force an exit of the while loop,and"continue"will force executionto retum to the while statementwherethe expressionis evaluated. I do not usethesestatementsbecausethey Personally, act asgotosin the program,changingexecutionwithstalements. out regardlo theslructuredProgramming And I do not recommendthat you usethem in your programs,asthey canbe difficult to debugand can leadan applicationto behaveunpredictably(especially if you are new to programming).

l5-The ForStatement Experiment PXekit*

L

The designof the for statementis actuallyquite ele"what are the gant andresultsfrom the question, requirementsof repeatingloops?"The statementformat ls: (Initializationi for Incr€nent ) Statemeat

I try to teachprogrammingasI wastaught,and that is to emphasizethe capabilitiesof the differentfunctions built into the languageand how to usethem approprF Somepeople,however,seemto atelyin applications. think they canusethe for statementin virtually any situationwhereconditionallyloopingcodeis required.I guessthe theorybehindusingthe for statementin different situationsis to reducethe numberof statement typesthat are in your programrninginventory.In this experimentand at the end to this section,I will show that the for statementis a wonderfullyflexiblestatement,but that it canmake codea lot more complexto understandand debus.

46

l.oop

'lesu

E {pressioni

Loop

and its operationis similarto the BASIC codefor a loop.Initializationis the processof initializingvariablesthat are (ideally)requiredfor the loopingoperation, but the processcan alsoincludeother assignment is an exPression. /oop testexpression statements.The similarto that usedin the while statementto test whetheror not the loop shouldrepeat.Finally,the /oop incrementstatemenlis normallyusedto incrementthe loop counterafter eachiterationof the loop. The for statemenlis typicallyusedwhenyou needa loop that repeatsa set numberof times.It might look like the following: (i = Or i < ua*Nlrrib€tt i++) for Executseal Repeatedllv // gtatenent slatementi nfor,, IJoop

l,e3 PICo llCUExperiments fon the Evil

Genius

by

and could be modeled as:

$rhi1e

(i

nvke prealko 04.11. 09

< Maxl{llmber)

{ Statementr i )

Executeal Repeateally Statenent \tfor,, Loop Equivalent to Ni++"

//

= i + 1r // elihw

//

by

CONFIG(INTIO & WDTDIS & PWRTEN & DTCIJRDIS& UNPROTECT \ & UIIPROEECT & BORDIS & IESODIS & ECMDIS) t

j..

int

In this for statement,a counteris initializedto zero and is incremented(usingthe "i+ +" statement,which is equivalentto i = i + 1) until it is equalto MaxNumber.This shouldbe quite easyto understandand usein your own applications. The useof the for statementbecomesmore complex whenyou considerthat multiple initializationand loop incrementassignment statementscanbe used (with eachseparatestatementseparatedby a comma). lf commasare not usedto separatethe assignment statements, the compilerwill becomeconfusedasto how to parse(convert)the statementscorrectly.The following for statementis completelyvalid: (i = 0, for Statetnentr

j //

= 47i i < MaJdilumberi i++, j = j Executefl Repeatedly Statement \forz Loop

lhrough

PICkit

This Program r,ri11 ro11 throuEh each PcB. rrEDs built inlo the Prckit The LED values

the

only

$for/'

PORTA = 0t ClilCONo = 7, ANSEL = 0r

// //

Tlvr'r off r'urn off

Conparators ADC

k = 0t

//

S!a!t

LED 0

for(rr)

//

r.oop Forewer

(i = 0r i < 255r i++) // for for (j = 0r j < !29t j++lt

- 2) by

I

k) && (0 == n)r (1 == k)u

n++)

for (rI = 0, (2 == { // Sinulate {if PORTA = 0b010000t TRrSA = 0b101011t | // tof for (n = 0, (3 == 'if { // sinulate PoRTA = 0b000100, TRISA = 0b101011, , // t.of f,o! (n = 0r (4 == { // simulate 'ig PORTA = 0b100000t TRISA = 0b011011t | // rof for (n = 0, (5 == trif { // simulate PORTA = 0b000100i TRISA = 0b011011t

k) && (0 == n)t (2 == k)/

n++)

k) && (0 == n)r (3 == k)/

n++)

k) && (0 == n)r 14 == k)"

n++)

k) a& (0 == n)r (s == k)/

n++)

+ 1)

% 8r

slatements.

5ection Truo

but

,

Delay

k) && (0:= (0 =- k)"

k = (k

to be 'cFor", explosive.

simple

f,or (n = 0r (0 == { // sirnuLate \if PORTA = 0b010000i TRISA = 0b00L111t j // '.of for (n = 0r (1 == t // simulate \if PORTA = 0b100000; TRISA = 0b001111t

for (n = 0r (6 == k) \if (6 { // sinulate PORTA = 0b000100, TRISA = 0b111001t j l/ rof for (n = 0r (7 == k) Nif (7 { // Simulate PORTA = 0b000010 t TRISA = 0b111001t J // rof

are:

The original nam€ was going that se€neal too potentially

at

{

r,ED Anoale Cathoale DO AA4 R.A5 D1 RA5 RA4 D2 RA4 NA2 D3 ai[2 RA4 D4 RA5 R]A2 D5 RA2 AA5 D6 RA2 RA1 D7 RA1 RA2 Using

nt

t

8 LEDE using

of

k,

nain( )

In this for statement,both i andj are initialized,and both variablesare changedin the loop incrementportion ol the for statement. To demonstratehow versatilethe for statementis,I havecreatedan applicationthat cycleseachof the PICkit 1 starterkit's eightLEDS.(It will be explained in more detail later in the book.) Ratherthan explaining how the for statementswork in the application,you shouldwork throughthem on your own (it's really not very hard-especiallywith the providedcomments). *include /* cPKr,ED 2.c - Ro1l oII].y \for?'

j.

//

// //

rr), n++)

&& (0 == n)t == k)/

n++)

&& (0 == n), == k)/

n++)

rncrement of o-7

IJoop

k within

Erl..l CPKI,ED 2

Introductory C Programming

range

For Eonsideration At the start of this section,I noted that C is notorious for its ability to allow programmersto createvery eff! programstatecient but very difficult-to-understand ments.In the lastexperiment,I showedhow the for statementis very versatileand how it canbe usedto replaceall the traditionallyusedconditionalexecution motivationfor writing complexstatestatements.The mentsis usuallyto minimizethe amountof keying requiredfor an application,althoughsometimesit can seemlike the author of the codeis simplytrying to demonstratehis or her mentalsuperiority. For example,in looking at an exampleapplication, you might run acrossa statementlike the following: * ?. Match = 0r (Malch = (i = (j = start) for (PORTC != (PoRTA ^= sequencelj++l))) && (i++ < 25)i r, // Sequence Match confirnation?

At fint glance,it is probablyimpossibleto understandwhat this statementis intendedto accomplish, and,to makemattersworse,the commentis no help at all asit doesnot seemto relateto anythingin the statement.You may feel like givingup and looking for anotherexample,but you can do this;you candecode statementslike this surprisinglyeasily. When I presentedthe for statement,I noted that it wasin the lollowing format: for

( Initial

izationr

lJoop TeEt

E:.pressioni

Lootr)

sta!emen!

stateand eachpart (whichconsistsof a C assignment ment or expression)of the for statementcanbe broken out into piecesand rewritteninto piecesthat make more sense.For example,the initializationassignment statementof the for statementis: i = ( i = s t a r t ) * 7 i

and takesadvantageof the ability of C to savean Becausej intermediatevaluein a complexexpression. is equalto Stafi and it is a factor in the initializationof the two following lines i, the authorhascompressed into one:

.

i = S t a l t * 7 t j = startt

Similarly,the comparisonexpressionof the for statementcanbe broken out andunderstoodby recogn2ingthat comparisonvaluesare arithmeticvalues (zerofor false,and not zero for true).To take

48

advantageof this point,lhe Matchv^riable (the first part of the comparison)is loadedwith the resultof the comparisonof PORIA (whichhasbeenXORed with a valuefrom the Szquencearray) to PORTC.When an arithmeticor binary operatoris placedbeforethe statement,the line is equalssignin an assignment translatedasthe destinationvalueoperatedon by the other parameter.I might write out the comparisonpart of the for statementasfollows: PORTA = PORTA ^ Sequencetilr

//

Same aB 'PoRTA

j = j + 1r // rnclemen! *r., "." ilT#"

" "

r{atch = 0t (PoREc == PoRTA) if Match = 1t

Both partsof the comparisonusethe unaryincrement (++) operatorto incrementthe variablesi andj d/€r the expressionhasfinishedexecuting.When the unaryincrementor decrementoperatoris put to the lelt of the variable,asin the following example ++J i

the variableis incrementedbeforethe statementexecutes.Similarly,if the unaryoperatoris on the right sideof the variable,the variableis incrementedafter the statementhasexecuted.I recommendthe useof the incrementand decrementunary operatorsin your coding,asthey are a lot easierto key than the completestatement j

= j

+ 1t

and they are generallyacceptedasthe shorthandversion of thesestatements, A null statementis usedfor the incrementpa of this statement.This is a bit unusual,but the unary proexpression incremenloperatorsin lhe comparison vide this function. Justasthe null statementis usedasthe for statement'sincrementstatement,a null statementis usedas the loopingstatementor statementsthat follow the for statement.If you look at how I havebroken out the you will seethat there is an comparisonexpression, assignment statementto PORIA, which could be movedto the loopingstatementareaof the for statement. If I wereto write equivalentcodeto the for stateit would look ment givenat the stafi of this discussion, like this: something i = S t a r t * 7 t j = start, tilatch = 0, ((0 == uatch) $hile

l , a 3 P I C o I I C t JE x o e n i m e n t s f o r

&& (i

the Evi]

< 25))

Genius

t

PORTA = PORTA ^ Sequenceli] t (PORTC == POREA) if Malch = 1r // s€quedce Malch Coafifinalion? j = j + 1, i = i + 1t ) // €1ihrt i = i + 1t j = J + 1,

You should be able to relate this code to the original,and I'm surethe commentmakesmore sensenow. What might not make senseis the incrementing of i andj after the while loop;thesestatementswereput in to make surethe valuesat the end of the equivalent matchthe valuesat the end of the orisinal for statement. In terms of readability and decodability,I am sure the seriesof statementsI havecomeuDwith are vastlv

superiorto the singlefor statement.In termsof efficiency,the number of instructions created for either solutionis not substantiallydifferenqnor is the execution speedof the two solutionsdramaticallydifferent. The major difference between the two statementsis the amountof keyingrequiredfor them;the sequence of statementsrequiresmany timesthe numberof the keystrokesof the short for statement. It should be no surprise that I recommendthat whenyou program,you avoidheavilycompressing statementsunlessa strongreasonexiststo do so. Although you may savea substantiallygreaternumber of keystrokegyou shouldaskyourselfhow much time you might later losedebuggingor decodingone compressedcomplexstatement.

h{ L C

n

9--, TU

TJ 4

Section Tr.uo I n t r o d u c t o r y C P n o g r a m m i n g

49

Section

Three

S i m p l eP I C @ M C UH p p l i c a t i o n g

Prc16F684 14-pin ZlF socket (3MlTextool 2L4-333900-0602J reconmended) 0. 01 p,F capacito! length of 283-foot 30-gauqe sol j.d core

Before goingon,I would like to walk througha modificationto your PICkitrM1 starterkit. This minimizes the chancefor damagingeither the PIC microcontroller you are programmingto put into anothercircuit or the PICkit 1 starterkit you are usingto programthe PIC MCU Although the PICkit 1 starter kit is an excellenttool, the machinedreceptaclesocket that is built into the PCB is not designedfor many repeatedplug/unplugcycles.Looking at manufacturer'sdatasheets, military-gradedual inJine chip package(DIP) socketsare qualifiedfor 48 cycles. The specifiednumberof plug/unplugryclesfor industrialgradesocketsis 50 times(althoughthey are not tested to seeif they meet this specification). As you work throughthis book and your own experiments, you will easilyexceedthe maximumnumberof plug/unplug cyclesfor a military-gradesocket,and chancesare at leastone or more pin receptacles in the socketwill wearout and stop makingreliablecontact.Youwill find alsothat pluggingand unpluggingpartsin the machinedreceptacleis difficult and that it's easyto bendthe pins,havethem fall ofl or get stuckin the PICkit 1 starterkit's sockets.You canavoid these problemsby adding a zero insertionforce (ZIF) socketto the PICkit 1 starterkit. Followthe stepsoutlinedhere.To add the ZIF socketyou will needthe following: 1 PICkit 1 starterkir with snap-offPCB still attached 1 14-pinZIF socket(3M/fbxtool 214-3339-000602Jrecommended)

51

or

1 0.01pF capacitor 1 3-foot length 28- or 30-gaugesolid core wire Weldbondglue Solder The toolsyou requireare asfollows: Solderingiron DMM with audiblecontinuity tester Needle-nosepliers Clippers Wire strippers A ZIF socketis similarto the machinedreceptacle socketalreadyon the PICkit 1 starterkit. The differenceis that the pin receptacles can be openedor closedby movingthe lever on the socket.The open positionis shownin Figure3-1,and the pin receptaclesare closedwhen the leveris pusheddown.This socketwill be addedto the open 14-pinDIP socket areaon the prototypingsnap-offPCB on the right sideof the PICkit 1 starterkit (seeFigure3-2),and eachpin will be wired to the correspondingpin of the machinedreceptaclesocketalreadyon the PICkit 1 starterkit. Expectthat this taskwill take an hour.

Figure 31 14-pin3M/TextoolZIF socket

Fiqure 3-a 14-pinZIF socketaddedto the prototypingareaof the PlCkit I storterkit

The stepsfor addingthe ZIF socketare asfollows: Solderin the ZIF socketwith its lever up (i.e., pin receptaclesopen).This will ensureproper operation.If you solderthe ZIF socketin with the lever down,you will find that the receptacleswill not open properly.You may find that you haveto prop up the PCB with ZIF socket to make surethe lever staysup during soldering. If, after soldering,you find that somepins stick or don't open easily,move the ZIF socket'slever up and remelt the pin's solderto seeif that relievesthe stress. 2. Using point-to-point wiring,add the 14 connections betweenthe machinedreceptaclesocket and the ZIF socket(seeFigure 3-3).Pin 1 of the PCB socketshouldgo to Pin 1 ol the ZIF

1.

52

Figure 3-3 Point-to-pointwiring usedto connect ZIF pins to PICldt I starterkit programmingsocket ptns

socket,pin 2 of the PCB socketshouldgo to pin 2 of the ZIF socket,andso on.When I have donethis,I try to keepmy strippedpin lengths to r/:z inch (1 mm).There are two rows of holes besidethe 14-pinsocketholesin the prototyping snap-offPCB;to theseholesyou canattach one side of the wires rather than soldering them to the pins of the ZIF socket.When you are addingthe wires,it is a good idea to leave the ZIF lever up to make sure that, rt the ZIF socketpinsremelt,therewon't be problems later with any of the receptacles. 3 . l e s t y o u rw i r i n gu s i n gt h em u l t i m e t ecro n l i n u ity testerfunction.Each pin of the machined receptaclesocketshouldbe testedagainstthe correspondingpin on the ZIF socket,aswell as againstits adjacentpins to make sure no shorting exists. 4. W h e ny o ua r ec o m f o r l a b lteh a ty o u ru i r i n gi ' correct,solderthe 0.01p,Fin the two holes abovethe 14holesusedby the ZIF socket.I solderedthe 0.01 pF capacitoron the backside of the PCB becausethe ZIF socketcoveredthe holeson the topside.When solderingin the capacitor,make sure the leadsare asshort as possible,that it lies againstthe PCB,and that it doesnot extendbeyondthe rubber feet on the b o t t o mo I l h e P ] C k i t I s l a r l e rk i t . 5 . T h e f i n a ls t e pi s t o g J u ed o l rn t h ew i r i n gu s i n g the Weldbondglue.If you put on a reasonably thin bead,the glue shouldset to a hard,clear consistencyin 6 to 12 hours.To make sure the wires don't extendbeyond the rubber feet on the bottom of the PICkit 1 starter kit, you may

l , e 3 P I C o l ' l C UE x p e r i m e n t s f o r

the Evil

Genius

want to hold down the wires with a weight or tie them down while the glue hardens.I use Weldbondbecauseit can be Dulledoff later without damagingthe PCB.

1 starterkit that will standan indefinitenumberof plug/unplugcycles. And, it is still connectedto the other functionsof the PICkit 1 starterkit, which allows you to experimentwith the LEDS,buttons,and potentiometerintedacesbuilt into the PICkit 1 starterkit.

Onceyou'vecompletedthe six stepsand the glue hashardened,you havea ZlF-socket-equipped PICkit

h* * ;ii:

" ; l;t fi ''5

ExFeriment17-Basi c Delags

inh i'rt.

iEnd = 235r jRnA. = 23st

// //

.-- 1

OutBifle l,oop value Inaiale Loop value

I!

nain( )

{

The cFlash.cprogrampresentedin the introductionto this book includeda simpletwo "for" statementdelay. For the application,I wanteda delayof a half-second (500ms) so the LED would flashon and off with a period of one second.Findingthe end valuesof the for statementswasdoneempirically;I usedthe simulator, asI will showin this programto time the delayand then adjustedthe valuesuntil the delaywasapproximately500ms.In this experiment,I wantedto go back to the cFlash.capplicationand seeif therewassome way in which I couldquantifythe delayso I coulduse it in other applications. To test the application,I modifiedcFlash.cslightly asyou canseein the sourcecodebelow: *incluale - Try /* cDlay.c

to

fluantify

Delay

VaLues

Ihia Program iB a rnodificalion of \cFlash.c,. u36al to qua.Dtify the value of th€ enat of the tlelay valiabl€a anal the time dl€1ay on the FlaBhitrg D0 I,ED. ThiB Drog!€m is !o be usetl with botb th€ prc16P684 ainulator andt the prckit x pcB with iEEtalLefl. RiA4 - I.ED Poaitive aA5 - I,ED Negative

Connecliolr Connectsion

0{ .05. 19

( INTIO & WD4IDIS & PICRTEN & UCITRDIS & _coNFIe I'NPROIIECT \ & I'NPROTECT & BORDIS & IESODIS & FCMDIS) t

anit

PORTA = 0t C M C O N o= 7 r ANSEIJ = 0r TRISA4 = 0; TRISA5 = 0t whiL€(1

(

// // //

tura off Comparalora turn off ADC Make IIA4/RA5 Outputss Jj!

== 1)

//

loop

Foreve!

//

BreakpoinE

,l 1

$oPo, i j

NOP()t aa4 = aA{ ^ 1r // €lihw ) // Entl cDLay

< iEnal; < jEndr

Eele

i++) // j++) t

//

Breakpoint

//

Toggle

Delay

roop

Eere

LED

il;

]

|-r:*

The first changeto cFlash.cfor this experimentwas to add two variables,iEnd andjEnd, that I could changeeasilyto testthe operationof the application. The secondchangewasto placetwo statementsyou haveneverseenbefore(NOP0) beforeand after the delaycode.The reasonfor the first changeshould be apparent:Thevariablesallow the loop valuesto be changedeasily without affecting the program statements. The secondmodificationaddstwo instructions that don't do anything,and I could usethem for breakpointswithout affectingthe operationof the applicationor breakingan instructionthat is usedmultiple timesin the application. The pointsmaderegardingthe NOPO;statements are probablyconfusingandmight not make a lot of senseat this time.First,the NOPO;statementsare replacedwith "nop" or no-operationassemblylanguageinstructions, which I will discussin more detail later in the book.And statedpreviously,the PICC LiterMcompilerNOPO;statementcanbe usedasa

5ectionThree S i m p I e P I C @l l C U A p p l i c a t i o n s

53

{*

breakpointwithout affectingthe operationof the C program.Second,you will find that the PICC Lite compilerhasa very efficientbuilt-in optimizer,which looks for opportunitiesto ffeate executablecodethat optirnizerwill is assmalland efficientaspossible.This try to reusecodethat performsthe samefunctionin diflerent partsof the program.Whatthe optimizer the considersto be the samefunctionis not necessarily samething you or I would considerthe samefunction. Therefore,you will find situationswhereexecution will jump aroundto differentlocationsin the applicaBy addingthe NOP0: tionswithoutapparentreason. you are putting an instructionexplicitly statements, beforethe start and after the end of the two delaytbr statements. To measurethe time of the delay,I enabledthe MPLAB@IDE simulatorandthen addedthe Stopwatchfunction (seeFigure3-4)to the project.The Stopwatchfunciion will count the numberof instructionsthat executeafter the start of the applicationor after beingreset. To measurethe delayfor differentvaluesof iEnd andjEnd,I put a breakpointat eachof the two NOP0; I did this by movingthe cursorto the line statements. wherethe NOP0;statementwasfound,right-clicking, and selecting"Set Breakpoint."I then resetand ran the program,and whenit stoppedat the first NOPO; statement,I clickedon the stopwatch'szerobutton to resetthe stopwatch,then clickedon the run button again,andwaitedfor the next breakpointto stopexecution. I wasexpectingthat the iEnd andjEnd valuescould be reversed.Thisis to saythat the delayof iEnd equal to 50 andjEnd equalto 100would be the sameasiEnd equalto 100andjEnd equalto 50.Thisturned out not to be the case;the delayvariedby severalpercent whenthe iEnd and jEnd valueswerereversed.Totry

Stopwdtch

and comeup with a simple,repeatableformula that couldbe usedfor the application,I tried makingboth valuesthe sameandcameup with the followingrough formula: Delay(seconds)

= 1.8(10-5) x iEnd

This formula is reasonablyaccuratefor the rangeof 50 ms to 2 seconds. Thinking aboutthe optimizerand thinking about the code,I realizedthat the optimizerdidn't do an obviousoptimizationand that is why I replacedthe two for statementswith the following statements: i j

= iEndtt = jEndt

Without anythinghappeningin the insidefor loop, the two loopsare not doing anythingother than exiting with i andj beingchanged.In this case,the for loop codeis still includedin the application,but you will find caseswherethe ultimateoptimizationthat I listed previouslywill be producedby the compilerand its optimizer. Delaysare criticaloperationsin microcontroller(or any real-time)programming,and I will be showingyou a numberof methodsto implementdelaysin your Although you might want to get your applications. delaysexact(in termsof time or instructioncycles), rememberthat this is often closeto impossibleand usuallynot required.As I discussdifferent applications,I will point out whetheror not the delay's absoluteaccuracyis criticalor if an approximation (usuallywithin 10percent)is acceptablefor the aDplication.

Totalsimddted

cycresf---1iDE67l-**iffii66' r -lI!.'| Inskuction l-

I

@l

q...l I a.n.nEr I r nA-n. rimeftsecsl l-----'iro-i6571-m Tiho

Requency IMHz) Processor

fllooo6''

It ClearSinulstionTirne0n Eeset

Fiqure 3-q

54

MPLAB IDE Stopwatchfunction

l , e l P I C @l ' l C l JE x p e r i m e n t s f o r

the EviI

Genius

t l t

ExperimentlB-Sequencing PlCkit1 StarterKit LEDs Table3-1 Plckit1StarterKit LEDUisplasTBISHand PoFTF Values

As you havegainedinsightinto PICC Lite compiler PIC microcontroller programming and the PICkit 1 starterkit, you haveprobablystartedaskingyourself how did I know to turn on the LED marked"D0" to make the PIC16F684's RA4 and RA5 pins outputs, and then output a 1 (or high voltage)and a 0, respectively. The processthat I went through is quite simple and only requiredlooking at the schematics for the PICkit 1 starterkit. It did not requireany probingor trial and error. When you look at the LED circuitryin the PICkit 1 starter kit's schematic(fowdin the PICkit I Flash StarterKit UserbGuide),yor seethat eachof the eight LEDs is wired aspart of a pair,like I showin Figure35.To turn on one LED, currentmustflow in one direction. and to turn on the other-currentmustflow in the oppositedirection.When I startedthis experiment,I hadhopedthat I couldmake activemore thanjust the two I/O pins connectedto the LED output.But whenI followedthe variousconnections, I discoveredthat if more than two I/O pins were activeat any time,there wasa good chancethat a secondLED would be inadvertentlylit. With this knowledge,Icameup with Table3-1, which lists the TRISA and PORIA register values neededto turn on eachLED on the PICkit 1 starter

LED

TBI5B

POETE

DO

B' 11001111.

B ' 0 0 0 1 0 0 00 ,

D1

B'11001111'

B'00100000,

D2

B'11101011'

B ' 0 0 0 1 0 0 00 '

B'1110L01"L'

B'00000L00'

D7

*s4

B' 11011011'

B'00100000,

B'11011011'

B'00000100,

B'11111001'

B'00000100'

B'111110 01'

B ' 0 0 0 00 0 1 0 '

t!t

! i

, ii

kit. To test this knowledge,Icameup with the following program, which turns on eachLED in sequence. The program usesthe samedelay that we usedfor the originalcFlash(flashingD0 LED) programto show clearlyif eachLED lit and if they lit in the correct order.Note that in the program,the informationfrom Table3-1 is part of the documentation. #idcLutl€ - RoIL /* cPKtED.c

Through

Prckit

8 LEDg

This Prograll will ro11 through each LEDg t'uilc inlo PCBChe PICkit The LED valuea

of, the

! ; I

e"f

are:

:- -

LED Anoal€ Cathotle DO RA4 RA5 D1 RA5 R]44 D2 RA4 RA2 D3 RA2 RAd D4 RiAs RA2 D5 RJA2 RA5 D5 RA2 RA1 D7 RJA1 RJA2

**'ti f 1 1r.

nyke 9retlko 04.09.10

! :

COIII'IG(ITVIIO & VIDITDIS & PICRTEN & UCIJR.DIS & I'NPROTIICT \ & IJNPROTECT & BORDIS & IESODIS & FCUDIS) t

PIC MCU l/O Pin

int

i,

j,

fe

k;

nain( )

(

P I CM C U l/O Pin Fisure3-5

*{ . !

LED wiring

PORTA = 0t CUCONo = ?r // t\rn ANSEIT = 0t // Tuln

off cdnlraratsors off A.DC

k = Ot //

IED 0

Start

a!

5ectionThree S i m p l e P I C @l l C l JA p p l i c a t i o n s

55

while(1

=-

1)

//

loop

Eolev€r

{

{J

r-(

P.{ v

Ft

o g

s, r.L{

z

f , o r ( i = 0 r i < 255r t++) // f o r ( j = 0 r j < L29i i++),

Si{E)le

(k) | / / seLect switch caBe 0: PORIA = 0b010000t TRISA = 0b001111t bleakt caa€ 1: PORTA = 0b100000t ERISA = 0b001111t breakt cese 2: PoRTA = 0b010000, TRISA = 0b101011, breaki cas€ 33 PORTI - 0b000100t TRISA = 0b101011t breakt gAB€ 4: PORIA = 0b100000t fRIsA = 0b011011t br€akt caEe 5l PORTA = 0b000100t rRISA = 0b011011t b!€akt caae 5: PORTA = 0b000100t TRISA = 0b111001, bleekt

r,ED tso Display

$..

k = (k

+ 1)

% 8i

6 'r.l

Loop

PoRTA - 0b000010, TRISA = 0b111001, b!6aki ) // hctiw8

h L.

wblch

Delay

//

) }

//

//

Incr€ment o-7

k wilhin

range

of

elihw End cPIGED

Looking at the program,its functionshouldbe fairly easyto understand. The largeswitchblock of codepassesexecutionto the seriesofTRISA and PORTA register wdtes that are specific to the LED to be written. I could have wdtten to individual bits rather than the entirepod, but I felt that the entfue port write waseasierto follow and understand. I would considerthis applicationto be quite large, clumsy,and not particularly well written. The use of four register writes per LED took a long time to key in (evenwith cuttingandpasting),and there wasa very goodchanceof makinga data entry mistake,or typo. As you work through the experimentsin this book, (particularlythe onesin Section4), think abouthow you could improve the way a piogram is written. For example,in this preyious example I believe I could reduce the total number of lines to lessthan a quarter and eliminatethe repeateddata valuesusedto tum on and then turn off eachLED. This program could be consideredan initial version of a Cylon Eye from BattlestarGalactica,which is also called a "Knight Rider Eye" from the TV show.After trying out the program presentedin this experiment, you might want to seeif you canmake the LEDs reversedirection after reachingone extreme.To do this you will requirean additionalvariable,this one storingthe directionof the LEDs and changingits valueeachtime the on LED is either D0 or D7. Along with the direction variable,you will have to make sure that theTRISA and PORTA bits are returnedto their originalstate(i.e.,loadedwith zerosfor output and in input mode) before tuming on the next LED in the seouence.

m II

Experiment l9-Binarg NumberOutputUsingPlEkitI StarterKit LEDE

t* ()

s

.l-l t . H

s

P{

X

In the previousexperiment,I demonshatedhow each LED on the PICkit 1 starter kit could be turned on in seouence. I notedthat onlv one LED couldbe turned

l;'rl 55

on at any time,meaningthat the PICkit 1 starterkit cannotsimultaneouslydisplaymore than one bit of data at a time. In this experiment, I will show how you can display an incrementing eight-bit counter on the eightbits of the PICkit 1 starterkit. The methodusedto displaydata on all eight bits simultaneouslyis the samemethodthat I will demonstratefor multidigit LEDS and dot arrayLEDs.To give the appearancethat all the LEDs are active at the sametime, we will rotate through eachLED in sequenceand, if the bit the LED is representingis set, then the LED is turned on for a set period of time. If the bit is not set.then the LED is left off for the same

l , e 3 P I C @l ' l C l JE x o e r i m e n t s f o r

the Evil

Genius

PORTA = O' elae // DiEplay the PORTA = 0b100000t TRISA = 0b001111,

amountof time.Thisensuresthat the brightnessof eachLED will be constantregardlessof the number turned on, and that constant timing for the application is provided.Thismethodis alsothe basisfor controlling multiple rnotorsand servos(asin a robot) and shouldnot be consideredapplicableonly to the devicesshownin this book. The rule o[ thumblhat I usewhensequencing LEDs is that eachone shouldbe turned on 50 times per second.For this application,IwantedeachLED to be on 100timesa second,which meansthat eachLED is turned on over a 0.01second(10 ms) period.For eachLED to be activein the 10 ms time period,it shouldbe turned on for 1.25ms (10 ms dividedby eight).Tocreatethis delay,I useda singlefor loop with the delayvaluefound empirically. The programI cameup with incrementsa counter onceeveryhalf a second,and the currentcounter valueis displayedon the eightLEDS of the PICkit 1 starterkit: *inclual€ - use /* cLEDDlEp.c counter Using IED at

\ePKLED.C,, 100x Der

LE'D Time

on Delay

f'J,

f,or (i = 0r i < Df,ayr i++)t ( (value & (1 << d)) == 0) if PORTA = 0t elae // Diaplay th6 va1u6 PORTA = 0b100000, TRISA = 0b011011t

\.L; i I

(i = 0, i < Dlayr i++)t for if, ( (value & (1 << 5)) == 0) PORTA = 0t elae // Diaplay the value PORTA = 0b000100, TRISA = 0b011011t

$=3" 6"{

(i = 0, i < D1ay, i++)t for ( (vaLu€ 5. (1 << 5)) =- 0) if PORTA = 0t €15e // Display the vaLue PORTA = 0b000100, TRISA = 0b111001;

as a base, cycl€ lhrough each secondl (1250 uB b€tlraen IJEDa).

//

tu

fo! (i = 0r i < DLay, i++)t if, ( (value & (1 << 3)) == 0) POREA = 0t else the value // Display PoRTA = 0b000100t TRISA = 0b101011t

nyke p!€tlko 04.09.12

in! i, jt in! Value = 0t ints Dlay = 67,

b!,1

(i = 0r I < Dlayr L++)t for ( (Value & (1 << 2)) == 0) if PORrA = 0t elae the valu€ / / Diar.lay PORTA = 0b010000t TRISA = 0b101011t

D0-D7 a6 an incrementing

& WMDIS & PIIIRTEN & IICIJRDIS -CONFIG ( IIIIIIO I'NPROTECT \ & I'NPROTECT & BORDIS & IESODIS FCMDIS) '

value

r-5 e.€'! *:S

for (i - 0i i < DLayr i++); i.f ( (valu€ & (1 << 7)) == 0) POBIA = 0t else the Va1ue // Display POREA = 0b000010t TRISA = 0b111001,

& &

j = j (i if

VariabLe

+ l, // >= 50)

Incremenl

lhe

Counter

d*.{

B.{

every

1/r g

{

tiS

value = value + 1t // Increments Digplay j = O, // Reaet the counter

main( )

{

frt' tn

Count€r

| // f.r PORTA = O' CMCONo - 7, // Tuln off cd|I)aratols ANSEIJ = 0r // I'urn off ADC J = o, whil€(l

//

R€set == 1)

tlre //

Dis!)lay

counte!

IJoop Eorever

{ NOPOT for (i = 0r i < Dlay,

t++)r

//

siry)Le Delay looD

( (va1ue & (1 << 0)) == 0) PORTA = 0t eLa€ // DispLay the Value PoRTA = 0b010000t TRISA - 0b001111, if

NOP O T (i = 0, fo! ( (valu€ if

i < DLayi i++); & (1 << 1)) == 0,

l }

/ / //

eLiYLw En.I CPKIJED

I chosethe 10 rnsdisplaytime becauseit allowssimple calculationsfor countinga setnumberof loopsfor largerdelays.I take advantageof this for inqementing the Valuevariable,whichis displayedon the LEDs Two pointsshouldbe notedregardingthe codeI usedto determinewhetheror not a specificLED is turned on in this experiment.The first is the useof shifting the bit ANDed with "Value" to seeif the bit in "Value" is set.Rather than putting in the decimal, binary or hexadecimalequivalentof the bit, I choseto shift one up by the bit number.By doing this,we can seeexactlywhat bit is beingANDed with "Value" ratherthan havingto do a mentalcalculation.You may

5ectionThree S i m p l e P I C @l l C U A p p l i c a t i o n s

5t

i?t

feel more comfortable using an equivalent value. Secondly, I choseto OR the value in PORIA with zero if the bit is not setto make surethat eitherpath takesup the sameamount of time. This can be extremely important in timed applications,and although it makesthe codea bit more complex,it ensuresthat your timing is asconsistentaspossible,regardlessof the path taken.

This program will be the basisfor displaying binary data in future experiments.I must point out that it is actually programmed in a very inefficient manner.In Section4, I will provide you with features of the C programming languageand programming techniquesthat will make this application more efficient both in terms of soaceusedand executiontime.

ExFeriment 20-Basic ButtonInFuts on RA3 is low,and then RA5 (DO'scathode)is pulled low.When the logiclevel input on RA3 is high,RA5 is driven high.The program,cButton.c,is quite simple: f!r...

:4 t

#incluale - Stnltl€ C Progra$ /* cButston.c rJED wh€n Buttotr La Prea8€al

x

Thl.6 Program

ia

a moalification

to

Turn

on a!

.cFlash"

of

&-* a:A3 - Button Con!€ctsLon a:A4 - IJED PoaitsLve Conn€cEio! a:A5 - IJED Negative CotrnecEion

g-*.*

f :

r:! :iY1 I

The simplestform of userinput you canput into a PIC MCU application is a button. This is usually accomplishedby a pulled-uppin with a momentaryon button that pulls the pin to ground(seeFigure3-6).The PICkit 1 starterkit hasa very similarswitchcircuit on RA3;it canbe usedfor eithercontrollingthe resetof the PIC MCU (whichwill be presentedlater),or it can be usedas an input with which you can experiment.In this experimentaswell asthe next one I will demonstratehow this switchcanbe usedasan input device.

nyke preflko 04.05.24

-CONFIG(IN:IIO T'NPRCTIECT \ ACMDIS ) t

& WDTDIS & I'IIPROTECT

& PIIIRTEN & BORDIS

& !{CIJRDIS & IESODIS

nain( )

{

The software for this experiment consistsof simply readingthe switchand then determiningwhetheror not the D0 LED on the PICkit 1 starterkit shouldbe turned on.When the button is pressed,the logic level

PORTA = 0n3F, // Atl Bits are Hish CMCONo = 7t // $En off. Cdll)arators ANSEL = 0, // Turn off A.DC TRISA4 = 0r // Uake RA{/RAs Outputa TRISAs = O' whiLe(1

(

P I CM C U

if,

== 1)

tooD

//

(0 == Rll,3)

//

Eorev€r

s€t velu€s ata!e[rent

usiag

*if"

{ RA5

)

.i'{

€lse

{ RA5 = lt

l // fr //

I )

b.t n!

//

elihw Endl cButEon

cButton.cis written asif the authorwasfamiliar with C, but had only recentlystartedworking with the PICC Lite compiler.In traditionalC programming,

Figure 3-5

Pulled-upswitch

58

l , a 3 P I C @I ' l C l JE x o e r i m e n t s f o n t h e E v i l

d\

Genius

whereno bit inputsare used,the button read and LED .

oulpul woulo plooaDly tooK |lKe Inls: if

(0 == (PoRra & (1 << 3rl

{ PORTA = PORTA & (0x0FF

ll

Ia

^ (1 << 5 ) ) r

on -tt--oz RA3 Hi.gh

Lon, Malt6 RAs IJow

//

'

( IIITIO & WDTDIS & PWRTEN -CO![FIG I'NPROTECT \ & I'NPROTECT & BORDIS FCI{DIS) t inr

else

{

PoRTA = PoRTA I (1 << 5) // , ll f.r

Hish,

Make RA5 Hish

*incluile 2.c - SirtrDlifieal C Prograll /* cBuwon an IED wb€n Butlon is PleEs€al Program

ia

a nodlif,ication

i,

:u

& IICIJRDIS & IESODIS

. '

;+

Jt

nain ( )

*1

(

!3

but the author,seeingthe definedpins in the include files,probablyrealizedthat the pins couldbe read and written directlyratherthan havingindividualbits ANDed and ORed asI do above.What the author probablydid not realizeis that an input pin valuecan be passeddirectlyto an output pin asI do in the followingcButton2.c:

This

mvke Dlealko

to

Tuln

on

of, scButton"

POBTA = 0x3Er // A11 BitE are High C!4CONo = 7, // \rt'l off Cdnpaialora aNSEIT = 0r // nrra off ADC TRrgA{ - 0, // uake 8A4/!tA5 outputa TRISAs - 0, whiLe(l

== 1)

//

a:l ir1

IJooD Eorever

{ RA5 = AA3; // Si.nE)Ier: // €lihw 2 ) // End cButlon

Pass Value

through

to

RA5

)

This is a fairly sirnpleoptimizationof cButton,but it illustrateshow the pin variabletype of the PICC Lite compilercanbe usedto greatlysimplifythe source codeof an application.

t--i

r,i\

n-L3 - Bulton Connection RiA.4 - LED Poaitive Conneclion RA5 - IJED Negalive Conaeclion

r*{ ':., r: ai.

Experiment2l-Debountring Button lnputs

r-1

raI

If you have some experiencewith digital electronic circuitqyou'll know that handlingbutton input is a surprisingly challengingtask with a bit of sciencebehind it, whichyou will haveto understandbeforeyou can processbutton inputsfrom the application. successfully The mostcriticalaspectof understandingbutton operation is to debouncethe incomingsignals.Knowing the cunent button state and how you want the application to work is integral.In this experiment,I will demonstratea simpleprogramto changethe stateof the D0 LED eachtime the RA3 button on the PICkit 1 starter

kit is pressed.I will demonstratealsohow the MPLAB IDE simulatorcanbe usedto verify the operationof an applicationbeforea PIC MCU is bumed with an application. Each time a switch (or button) state changes,the contactsliterally bounceagainsteachother asshownin picturedin Figure3-7.Thishappens the oscilloscope both when the contactsare madeandwhen they are broken.To interpret,or debounce,thechangein switch state,the line is typicallypolled until it staysin the samestatefor 20 ms The basiccodefor polling a switch input line and exiting when the line has changed state for 20 ms is asfollows: i = 0 , I / waIE 20 ms fo! !,rhi1e (i < Twentt|ms ) t

Butlon

SectionThree S i m p l e P I C @l l C l JA p p J . i c a t i o n s

tp

59

l. tt

t

:

(0 == a.a3 )

if

//

Butlor

Down/Slarl

ov€!

t = 0t

i

) else

//

qp/IncredFnt

Buttson

counl

{

sl

| ,

i = i + l t // El eLi}lw /l

NOP()t i = 0, // Wait 20 rns for (i < llwenlyns) rdhile (1 == RA3) // Bulton if else // Bulton i = i + 1t RA5 = RA5 ^ Ii

Figure 3-7

Debounce

l

LJ

) (0 == RA3)

if

"

//

Button

Dowa/Stsalt

over

{ = 0t

i

) €ls€

Butston

//

UDllacrement

CouDt

{

b&4

= i

i

+ 1t

, // f.r //

)

elihw

Using this codesnippet,the following cDebounce.c applicationwasdeveloped: *incluile /* cDebounc€. c - Debounc€

Butlon

Iry>ut

oa na3

ThL6 Program polla lb€ bullon at RA3 anal cha.dgeB tlt€ atate of Rias aft€r lhe DreEa haa beeD alebounceal. use a 20 ns al€bounce perioal.

r6{ f,'$

RA3 - Butston CorbectLon RA4 - IJED Poaitiv€ ConaectLon RA5 - IJED Negativ€ Connectsi.on rryke Dretlko 04.11.07

i!

qi€

-CONFIG ( INTIO & 1iID!DIS I'NPROIIECT \ & I'IIPROFECT FCMDIS) ' iDt

,;di

$"{

dr

int

Tw€ntf'ms

-

1150,

//

Declar€ a Coaataat for 20 mE Delay

naia ( )

t POR!a = 0x3Fi // All Bits ere High Cl'lCONo = ?t // 'I'ttta ol.t Colll)alators AI{SEL = 0r // Turn of,f, ADC TRISA{ = 0t // Make RA{/RAs Outputs TRISAs = 0t whil€(1

,&

& &

it

consl

w

& PWRTEN & IICLRDIS & BORDIS & IESODIS

{ while

== 1)

//

IJoop Forever

/ / ttlaiE 20 I[s (i < Twent!,ms)

for

Bulton

UI)

// //

Butslon ltDlslarts

Down/Incr€drent

ll

'loggLe

Dolrn

Rlas to

over

Count

Tuln

r,ED

elihw End cDebounce

In the cDebounce.capplication, I first wait for the RA3 line to be high for 20 ms and then I wait for RA4 to be low for 20 ms before toggling the D0 LED output state.In the applicationcode,for the first debounceloop (debouncingbutton goinghigh),I addedall the bracesfor conditionalcode.But for the seconddebounceloop (debouncingbutton goinglow), I eliminatedthe extrabracesbecauseonly one statement appearsafter eachconditional execution statement, and thesestatementstake up a relatively large amountof space.For the restof the book, I will be usingbracesonly whenmore than one statementexecutesconditionally. The NOP0; statementmay seemout of placein this apptcation. When I wrote this application, I found that I could not placea breakpointat the i : 0; statement following the first debounceloop,so I put in the nop instruction,which gaveme a placeto setthe simulator breakpoint.Thisis a goodtrick to rememberwhenyou are developing your own application. You might think that the first debounceloop (debouncing the button input going high) is redundant or not neededbecausewe just want to executewhen the button is pressed,but you must rememberthat the The debounce PIC MCU is operatingat MHz speeds. and LED toggleoperationexecutesvery quickly,and, without the button up debounceloop,you'll discover that the LED togglesat roughly 50 times per second rather than once,eachtime the button on the PICkit 1 starterkit is pressed. Before I burnedthis codeinto a PIC MCU on the PICkit 1 starterkit MCU,I simulatedit usingthe MPLAB IDE simulator. If you were to enable the simulator and start executingthe code,you would discover that it would get stuckin the f st debounceloop becausethe defaultvalueof RA3 is 0 (or a low logic level).Tochangethe stateof RA3 in the simulator (and add a digital signalinput),you can usethe

{

60

oN/oFF

l,e3 PICo l"lClE J xoeriments fon the EviI

6enius

A number of different options exist for defining stimulus.In this experimentI simplyworked with predefined pin stimulus,but you can also specify asynchronouspin statesusing the Pin Stimulus tab.To changeor set specificpin states,click on a button on the window.When you specify the predefined pin stimulus for eachrow,you will haveto specifythe followrng:

ft*[1@

. Figure 3-B

Stimuluswindow

MPLAB IDE Stimuluswindow shownin Figure3-8. The importantpart of the stimuluswindow is the area the at the bottom,whichlooks like a spreadsheet; changinginput pin valuesare specifiedalongwith the time (numberof cycles)the changetakesplace. To set up the stimulus window, you will go through the following steps: 1. 2. 3. 4.

5.

6.

Click on the Debuggerpull-down,and click on "StimulusController." In the MPLAB IDE Stimuluswindow.click on the File Stimulustab. Next. to start a stimulusfile. click on 'Add" in the Input File Box, and selecta file name. Make surethe stimulusfile nameis highlighted and click on "Edit" in the Input File box to bring up the spreadsheetJikeinput area. Click on'Add Row" and then selectthe desiied options(discussedin the following paragraphs)to build an input waveformio the applicationcode.In Figure 3-8,the stimuluslist puts the input line high,glitchesit down,and then holds the line low.

. .

. .

cq! &3 @

s 5J

&"' ;t

Tiigger On-either after executingfor so many instructioncyclesor when executionhits a specific address.For most pin stimulusapplications,you will lvant to trigger on a set number of instructioncycles.Thespecificaddressfunction is usefulfor applyinga test value to an internal register. TiiggerValue-the number of cyclesor addresses. Pin/Register-the I/O pin or hardwareregister to be written to. More than one pin or register can be referencedin a singlestimulusfile. Value-the 1 or 0 for a pin or a hex value for a register. Comments-gives you a chanceto note what is happening.

In previousversionsof MPLAB IDE, stimulusfiles wereproducedby a text file that wasloadedinto the simulator.The cuffent Windows version makes it easier to implementsimplestimulusinputslike this one, but I feel that for more complex operationg the Windows version is a lot more work and more difficult to implement correctly.If you have a complex stimulus for the MPLAB IDE simulator,I suggestthat you write it out fi$t and then enterthe datacarefully rather than on the fly, asI did for this application.

Savethe stimulusfile and then define and save the project'sstimulusfile (click "SaveSetup"in the File Stimulusbox of the Stimuluswindow).

{&

ry $

il.} A,r

iN : t' +tr

rh

t ,

N

s

{"J {U

*"$ nr

v' ._*

Experiment aa-_MELFIOperation I-ooking back at the first book I wrote about the PIC microcontroller,I wasamazedat the amountof spaceI devotedto the topic of resetand the -MCLR pin, which is usedto control whetheror not the PIC MCU is to execute. The PIC MCU I wrote aboutin that book,the PIC16F84,requireda separateresetcircuit that,ideally, held the PIC MCU resetuntil the power supplyramped up to the operationvoltage,held off clock start until

5ectionThree S i m p I e P I C @l l C U A p p l i c a t i o n s

61

,rl

fd ${ \v >.-l

*-{ f l re'{ I I t

{'"f

ry +)

s! s "*l

any initial fluctuations had passed,monitored the power supply,and reset the microconholler if it fell below a specificvalue, aswell as allowed the user to control the operation of the PIC MCU. Although some shortcuts existed,they could be irnplemented only if you understood the application and PIC16F84operation well and if you understood what the tradeoffs of the selectedmethodwere.One of the big changes sincethen is the sophisticationof the reset circuitry mostof theseissues built into PIC microcontrollers; are no longera concemwhendesigningPIC MCU applications A completeresetsolution for the PIC16F84is shown in Figure 3-9 and takes advantageof a chip like the PanasonicMN18311 reset supeffisor chip.This chip will not allow the microcontroller to executeuntil the input voltage has had a chanceto stabilize,and if the power supply voltage drops below a specificpoint (known asbrownout, the PIC16F84will reset.Not only does a modern PIC MCU have the voltage-monitoring hardware built into its reset circuitry, but it is also able to work over a much larger voltage range (from 2.0volts to 5.5volts comparedto 4.0volts to 5.5 volts for the PIC15F84),so brownoutsare muchlessof a concern. The PIC16F684hasthe built-in resetfeatures includingthe brownoutdetectionand built-in start-up delaythat wererequhedto be addedto PIC16F84 Along with thesefeatures,the new chip applications. includes a number of bits in the STATUS and PCON registers(listedin Table3-2)that canbe polled to help determinethe causeof a PIC16F684reset.For most applicationgthesebits canbe ignored,but in some casesit is importantto understandwhy an application hasstarted executing. For this experiment,Iwould like to demonstrate how the reset pin (also known as-MCLR) can be used to resetthe PIC16F684while poweris active.And by polling the _POD bit of PCON the programwill indicatewhetherresetwascausedby power on or by making the _MCLR (RA3) pin on the PIC MCU active. Normally,I disable the -MCLR function of the RA3 pin and rely on the internal hardware to properly reset the PIC MCU. For this cReset.cexperiment, I enabled _MCLR and usedthe button on the PICkit 1 starter programis kit to causea resetof the PIC16F684.The basedon cPKLED and when the program first powers Vcc

& t a.{ tr: i?t

Signalto Microprccessor

Fisure3-9 MCU reset

62

up and -POR is low, I set the program to run so the LEDs will light in incrementalorder.On subsequent power ups,if the CPKLED bit is set,then I run the LEDs in decrementalorder. *incluale - RoIl /t cRese!.c

Prckits

Tlrrough

S rrEDE

each roll through ThiE Plogrem will intso the Prckits PcBrJEDE buiLl Th€ LED values

of

the

I

at6:

IJED Anodle cathoale DO RA4 RA5 D1 AA5 RAII D2 A;A4 !lA2 D3 AJA2 R,A4 D{ RAs N,A2 D5 AA2 RA5 D6 BA2 RA1 D7 RA1 RAz rq'ke prealko 04.09.10

( INTIO & TiIITIDIS & PWRTEN & MCI.REN & -COIIFIG I'NPROTECT \ & UNPROTECT & BORDIS & IESODIS & FCMDIS) t of \IICIJRDIS' // llotse \!{CLREN/ insteatl

int int

i. j, kt Polarityt

naia( )

{ PORT.a, = 0, CUCONo = 7t ANSEL = 0t

// //

Turn Turn

k = 0t

//

Stsalt

at

//

Check UD

PCON Resister

if

(0 == POR)

(

= 0t Polality poF. = 7, // rntlicat€

off off

ConrDaratora lU)C LED 0 for

Star!

Prc ltcu Powerefl UP once

) 6La€ PoLallty while(1

(

// Reset = Lt ll == 1)

//

Go Backwardls Loop

Folevet

(i = 0, i < 255t i++) // for f o r ( j = 0 t J < 1 , 2 9i j + + ) ,

siry)le

s w l E c h ( k ) ( // select caa€ 0: PORTA = 0 b 0 1 0 0 0 0 , TRISA = 0b001111, b!eaki

rJED tso DisDlaY

PORTA = TRISA = breaki case 2 r PORTA = TRISA = breaki

l , e 3 P I C @M C U E x o e r i m e n t s f o r

lihich

0b100000t 0b001111t 0b010000, 0b101011,

the Evil

Genius

D€l'av I,ooD

cage 3! PORTA = 0b000100t TRISA = 0b101011t bleakt

Table 3-2 for IndicatingBeasans for Bits FlesDonsible FlEset

PORTA = TRrSA = breakt case 5: PORTA = TRIaA = breaki cas€ 5: PoRTA = TRISA = breakt

Bit Name

0b100000t 0b011011t

0b000100t 0b011011t

0b000100t 0bU1001,

(0 == Po!.arity) k = ( k + r l % a i / /

elBe k = l ] E - L r % a r / /

)

//

racrement of 0-7

k within

Decr€nent

k within

Enfl cReael

0

Function

_TO

STATUS,4 Normally Set,Resetafter aWatchdog Timer Reset

_PD

STATUS,3 Normally Set,Resetafter Executinga SleepInsffuction

r )

F*

ULPWUE PCON,s

Set to Enable Ultra Low-PowerwakeUp

SBODEN PCO\4

SoftwareBrownout Detect Enable

PoRTA = 0b000010t TRISA = 0b111001t bleak, ] // hctiws if

negislef BiT

l.'J

th r!.t L !

POR

PCO\1

Reseton PowerUp-after PowerOn SetBit

BOD

PCON,O

Unknown Value on Power Up PowerOn Set Bit

e3

after

t "1

For virtually all applications that you create,you can safely disable the _MCLR pin and use it as an input-only pin. The only circumstancewhere I would expectyou to enablethe -MCLR pin is whenyou are debuggingan application and expecting the application to fail and hang up periodically, requiring a lowresetvalue.

r ir1 !|"J

*{ ct I

23- E n d i n g F p p l i c a ti o n s E x F er im ent

DFf

throughD2) in sequenceand then end.I enabledthe -MCLR pin so the applicationcouldbe restarted rather than requhingyou to downloadit againto start the executionprocessagain. *incluale - I,ighl /* cEud.c lghis lhen

Before goingoff to rnorecomplexapplicationEI thoughtit would be usefulto discusshow your PICC Lite compilerapplicationexecutesin the PIC MCU. In particular, the manner in which the hex code is loaded andexecutedmay be confusingand,therefore,worth discussing.You are probably familiar with running programsin your PC: when a program ends,control doesn'treturn to the operatingsystem.Obviously,this is not true for the PIC MCU, which doesnot havean operating system;so you might expect that when the programcompletes, the PIC MCU just stops.This experimentwaswritten to test this expectation. The cEnd.c application waswritten for the PICkit 1 starter kit. It will turn on the first three LEDs (D0

SectionThree

Proglarl Enfl,

3 LEDg anal Return

will

Lighl

D0 to

D2 Ltr Seguenc€

anal

rDJake pretlko 04.09.12

i, J, iEnal = 235i

t5r

f t

-CONFIG ( INTIO & WIiIDIS & PI{RTE!{ & IICI,REN & IJNPROTECT \ & T'IIPROIECII| & BORDIS & IESODIS & ECUDIS) t

int int

tsr,,

//

:, Seconal D€lay

nain( )

t PORTA = 0, O(xlICONo- 7r // '!J.tin of.f conparalorE aNSEL = 0; // Turlr of,f, A.DC PORTA = 0b010000t

//

D0

S i m p l e P I C @l l C U A p p l i c a t i o n s

63

TRISA = 0b001111; f o r ( i = 0 r i < i E n i l t

silrp1€ Delay for D0

f o r ( j = 0 r j < i E n a l i PoRTA = 0b100000r // TRISA = 0b001111t f o r ( i = 0 r i < i E n a l t

j++)t D1 sirE)le D€lay fo! D1

f o r ( j = 0 r j < i E n d t

j++)t

PORTA = 0b010000, // TRISA = 0b1010U, for(i=0ri
i++ )

f o r ( j = 0 r j < i E n a t t

j++)t

PORTA = 0b000000r

//

Retula stale

//

Delay sinple f.oi D2

PORTA to

Initial

TRISA = 0b11u11t // // l

U , f-t

*r ; i,! \t, '".d 'P.

ill

l

t

=- L), // lrorrral Enal whtle(]. SIJEEPO, // Allernative Endl //

Enal cEntl

When you run the programasit is presentedhere, you will discoverthat insteadofjust stoppingat the end (D2 turns on and then off), D0 lights again and the programseemsto run again.I suggestthat you now run it on the MPLAB IDE simulator,put a breakpoint at the first statement(PORIA : 0;) and at the last statement(TRISA : TRISA | 0b011111111), and start the programexecuting(with the stopwatchdisplayed).Theftst time the programexecutes, it will stopat "PORTA : 0;" indicatingthat it hasexecuted in 100instructions.Click on "Run" againand the program will executefor a few momentq finally stopping at the "TRISA : TRISA I 0b011111111;" statement with 3,006,075 executedinstructionson the stopwatch. Now,click on "Run" a third time.You might expect that the simulatedPIC MCU neverstopsexecutingor that it immediatelystopsand resetsthe simulatedPIC MCU. Actually,neitherhappensiexecution returnsto the first breakpoint(PORIA : 0;) and the stopwatch displays3,006,175 instructions. From theseresultsyou canconcludethat programstartsagainafter 100 instruction cycles.What is happening is most easily illustratedwhenyou are familiar with assemblylanguage,but the short explanationis that whenthe PIC MCU reachesthe end of programmemory,insteadof stopping,the programcounterresetsitself and starts executingfrom the start again. To preventthis from happening,Inorrnallyendmy programswith a statementlike the following that puts the PIC MCU into a hard loop that executioncannot escapefrom: whtL€(]. == 1),

h-

Although you will seethat I have noted this with a comment(or "commentedit out") in the previouspro-

64

gram,to testthe operationof this statement,deletethe two slashesto the left, rebuild,and retry the program. You will find that it will stop after D2 hasbeenturned off andwon't start until you press"SW1" (the reset button) on the PICkit 1 starterkit.Along with the while foreverloop,you canalsousethe SLEEP0; PIC MCU instruction,which is set off asa commentafter the while statement.Thisinstructionputs the PIC MCU into a low power state,and then allowsit to be restartedby pressingthe resetbutton on the PICkit 1 starterkit. In mostmicrocontrollerapplications, the programis continuallylooping,so the needfor the while statementor sleepinstructionis not required. But in applicationswherea singleoperationis being carriedout (like the examplesin this book),you will needthe while statementor sleepinstructionto prevent the programfrom executingrepeatedly.

For Consideration So far in thisbook,I havereliedupon the PICkit 1 starter kit exclusivelyfor putting in the circuitry but you canbuild thesecircuitson a breadboardvery easily if you have a limited number of PICkit 1 starter kits available(suchasin a classroom). Another casein which you might want to build a PIC MCU circuit on a breadboardis when you require different circuitry than is availableon the PICkit 1 starter kit. In the following paragraphs,I will quickly introduce you to putting a PIC MCU on a breadboardandsomeissuesthat you should be aware of when building your own circuits. The basicparts required for wiring a PIC MCU on a breadboardincludethe following: 1 Smallbreadboard 1 Breadboardwiring kit 2 AA or AAA batteriesand clip with breadboard wires 1 0.01mF capacitor(any type) 1 Powerswitch(E-Switch'sEG1903is recommended) LEDs Capacitorsof variousvalues Optional parts that you will want include the following: Pushbuttonswith breadboardwires Potentiometersof variousvalues

l , E 3 P I C @I I C U E x p e n i m e n t s f o r

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Smallplasticpartsbox The toolsthal you will rcquire includethe followlng: Smallflat screwdriver pliers Needle-nose Wire clippers Wire strippersor knife This probablyseemslike a modestlist of partsand shouldnot costyou muchmore than $20.00,and with them you cancreatea wide variety of differentPIC MCU applicationsoutsideof the breadboard.What of the two "radio may surpdseyou is the usefulness batteries"that togetherprovide about3 volts (for alkalinebatteries).The PlC16F684(and most other new PIC MCUs) will work with voltageinputsranging from 2.0to 5.5volts.Many modernperipheraldevices alsowork at thesevoltagelevels,so rather than using somethinglike a 9-voltbatteryand a voltageregulator to get 5 volts,you cansimplily your circuit by powering with two radio batteries.A completekit is shownin Figure3-10and canbe purchasedfrom a varietyof sources(includingRadio Shackand Digi-Key). The kit consistsof a breadboard,a breadboard wiring kit, someLEDs, resistorsor dilferent values (100Ohms,220 Ohms,330Ohms,470Ohms,1k,and 10k are goodvaluesto start with), capacitors(0.01pE, 10 pF,and47 pF will be useful),a momentaryon push button,an SPSTswitch,and a two-cellAA or AAA batterypack.As you createmore complexapplications,you will probablywant to expandthis kit. It would be a goodideato get a smalltool kit aswell.

Pin throughhole (PTH) chips(like the PIC16F684 and breadboard microcontroller),resistors,capacitors, wiring work without any modificationsto the brcadboard and only a few to someof the components. Although it will take a bit of work. For a power switch, the E-SwitchEG1903SPDT (availablefrom DigiKey) will work with a breadboardwithout modification. Unfortunately,I havenot found a momentaryon switchor batterypack that will work with a breadboard without modilication;I solderwiresonto standard partsasshownin Figure3-11to get this capability. Onceyou havethe parts,you canwire togetherthe cFlash.ccircuit (Figure3.12)in just a lew minutes,and the resultingcircuit shouldlook somethinglike Figure 3-13.Although the circuit seemsquite simple,there are threethingsto be awareol The first is to wire both sidesof the breadboardwith power (Vdd/Vcc) and ground(Vss/Gnd)on the commonbarson both sides of the breadboard(seeFigure3-13).This will n.rake your wiring simplerwhenyou havemultiple devices

Figure 3-ll AAA batteryclip and momentarypush buttonmodified with breudboardwiressoklereclt
#

2x 'AA' Baitery

-: -f I

Figure 3-110 Breadboard with basic parts neetled to run the PIC|6F84

.L

VSS

Figure3-le

Breadboard

5ection Three S i m p I e P I C @l l C U A p p l i c a t i o n s

circuit

6s

o! E P

2x'AA' -: or'AAA': Battery: Pack

t LED Can Ptc

Figure 3-lq Figure 313 Breadboard wiring to demonstratethe cFl.ash.coperation

on the breadboard and you won't have to crossover chips wheri you are connectingpower and $ound. Secondly,make sure tJrata switch is located on the positive terminal of the battery pack before power s passedto the common bars on the breadboard,and don't just place the switch on the Vdd pin of the PIC MCU chip @in 1). ff power and ground are available on other pins of the PIC MCU, you will discoverthat it will run, even if no connection to the Vdd and Vss pins exists.The clamping diodes on the UO pins of the PIC midocontroller will allow current to passtlrough them asshown in Figure 3-14,and frequently this will

Parasiticpower

be enoughto run the application.This is often called parasiticpower ard.problems with it can be avoidedif you control power at the source,rather than at the PIC MCUchip. It's important to remember to remove gently the PIC MCU chip after programming and insert it before reprogramming.The easiestway I have found to remove chips is to stde a small flat-blade screwdriver under the chip and twist; it will pop up from the breadboard. Before inserting the PIC MCU chip, make sure all the pins are aligned before pushing the chip onto the breadboard.You can even roll the chip on a table top to bend the pins inward. Bent pins can be straightened using a pair of plie$, but by taking a bit of care, you'll never have to.

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Four

Section

f LanguageFeatures type at the start of the file name for two reasons.The first is so I can use the folder name to differentiate betweensimilarprograms-thosecodedin C or assembler. The secondreasonis that the extensionis not displayedin the folder window of Microsoft Windows,and I want to make sureI know at a glancewhat language theprogramis writtenir.. The main part of the file name (Function, in the previous convention line) is simply what the program does.Personally, I would like this to be arbitrarilylong so I could createfile nameslike "SingleButton Debounce,"but the 64-character limit imposedby the MPLAB@IDE simulatormakesthis difficult. So I stick to a single surnmarizingword. If I am going to produce multiple versionsof the application,I keeptrack of them by a versioncodeseparatedfrom the rest of the file nameby a blank.

In this section,I will presentmany of the advanced features of C that will help you more efficiently program your applications.Thesefeatures allow you to more quickly create applications that are smaller,run faster,and handle data in different formats.Before I go on to the more advancedfeaturesof C.I would first like to addressthe topic of makingyour applications more readable. Readability of a computer program is a function of five different parameters: e

Appropriate file name

.

Header information

. .

Intelligent comments Adherenceto formatting conventions

.

Conventionalstatementusage

Remember to keep eachapplication in its own separatefolder.Multiple applicationsin the samefolder (or evenon your PC's desktop)are difficult to sort through to find specific applications.By keeping every applicationin its own folder,you will easethe workload requiredto find a specificapplication,help you managethe applications,and identify which ones are neededandwhich aren't. Every programshouldhavea headerblock with the following information:

This list of parametersshould not be surprising,but I am amazedat how few peoplethink to usethem when they are under a deadline.Actually, theserules often fall by the waysidein normal programming,causing a lot of grief whenit's time to go back and try to fix somethingor evento usethe codein anotherapplicauon. The filenamethat I haveusedfor the codepresentedin this book and the folder in which it is stored followsthe convention: nl"anguag€extl\rnctioaI

ftselalionl

.languageext,rr

"Languageext"is "c" or "asm,"dependingon the languagethe applicationis codedin. I put the language

. . . . .

Summaryof programoperation Detailed descriptionof what the program does Hardware information Author's name Date last updated(ideally with comments explainingwhat wasdone)

The purpose of most of this information is to allow you or somebodyelseto scanthroughand seeif this is the applicationrequired.You might be looking throughpreviouslywdtten applicationsfor samples that use specific hardware,or for a particular application that requires a fix.

67

Intelligent comrnentsexplain the purpose of a block of code.How the codeworks shouldbe selfexplanatory. The following is an example of what not to wdte: I

= i

+ 1r

//

Incteneut

Couat€r

i

This comment is not helpful asyou would assume that the readerknowsC well enoughto understand what the codeis doing.Insteadthe commentshould explainwhy the codestatementis there.A better comment for the statementmight be:

i = i + 1'

,A

0)

t{ Fi

{J

d \y [&l

ry

b d

"::::1":::'"::"*

In university,Ihad a professorthat took marks away for every comment in an application.His logic was that the code should be written in sucha way that it is self-commenting.I can seehis line of thinling, although it is probably the other extreme of voluminous,redundant commenting.I would suggestthat you follow the rule that commentsshould only add information. When you've been taught to program and when I have presenteddifferent statementtypeq they are formatted in very traditional ways.You may be unaware that C and mostother highJevellanguagesare very loose with their formatting, and an if statement like this one:

bt

i f ( A > B ) i = i + 1 ,

6 *4 t \

j

is just asvalid to the compiler asthe traditionally formattedstatementlike this one:

! i f

f.t't

o

( A > B ) i = i + 1t

eLse j = J + 1 ,

\J

r,t

+ 1,

(J is the endingof thestateIn C, the semicolon ment. Until the semicolonis reached,the statementis parsedasif it were all on the sameline, or formatted traditionally. You might think that a different statement format will make the application more efficient, but it will only make it frustrating for others to read and debus.

'r{

When I am formatting code,the rules that I use are as follows: . . .

.

Each statementis on its own line. Nestedconditionalexecutionis indentedby four spaces. If statements are longerthan lhe page(or screen)width, find a natural break and start them on the next line, indentedfour spaces from the start of the previousline. Commentsall start on the samecolumns.

Simple,clear code that is written in a consistentformat that is easierto read-even if it is formatted differently than you are usedto-than code that doesnot follow a single format and usesdifferent conventions for indentations and variable names.For example,the numberof indentationspacesI suggestis basedon whatVisual C11usesand I havebecomeusedto.You may find that two or eight spacesfor eachindentation makesmore senseto you. I do have one warning regarding indentations.Try to resistthe urge to rely on tab characterswhen moving code or commentsto a specificcolumn;use spacecharactersinstead.Different editors and web browsers interpret tab charactersdifferently, and by using tabsin your code,you will find that your neatly organizedprogram will becomevirtually unreadablein other tools. The final comment is similar to the previous one.As shown,C is a remarkably flexible language,and there are a lot of different waysof doing things My recommendation is this: Do not try to be creative in how you codeyour applications.Instead be asconventional as you can.Thespacesavingsandspeedimprovements(if any) madeby creatively organLing the code of your application will be offset by the increaseddifficulty reading and understandinghow the code works.I put the caveat"if any" in parenthesisbecausethe optimizer in the PICC Literu compiler is very sophisticatedand very good at identifying situationswhere repeatedcode is integrated into a subroutine or even reorganizingthe code to avoid redundant blocks of code. To summarizethis introduction, I quote the credo of the poor coder:"If it was difficult to write, it should be difficult to read." And the corollary is also true: If you work at making your code easyto read, you will find that it is much easierto wfite. The added benefit will be that your teachers,supervisors,and coworkers will appreciateyour efforts over those programmerswho do not try to make their codeeasierto read.

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Experiment 2t-.1-Functions and 5ubroutines

t.?

Functions are very similar to subroutinesexcept they retum a singlevalue.The declarationstatement for a function is very similar to the subroutine,but differencesbetweenthe two relateto the declaration statement'sability to return datato the caller: (ty9e var1, zunctslonNam€

type t //

If you were to Google@ the C programminglanguage for a definition,you would discoverthat it is "procedurally based."Thismeansthat the languageis designed to implement subroutineseasily so that prograrnming taskscan be brokendown into smallerpiecesfor easier programmingand reducedopportunitiesfor errors. Subroutinesin C will allow you to simplifyyour program, but I am more excited about C's ability to create functiors ,which offer much greater utility to your applications Just so the terms are straight, I usethe word rnvoke synonymouslywith cal/ when I am referring to subroutinesand functions. Subroutinesin C are declaredin the followins format: SubroulifleName

( t].D€

Var1,

...

{ // |

gubroulin€ //

)

stat€drentB her€

EnA subroutineName

and musteitherbe declaredbeforethe subroutineor a prototypehasto be placedbeforethe subroutineis used.This prototlpe consistsof the subroutinedeclaration statementwith a semicolonafter the input parameters.Prototy?es are often placed in include files (endingin .h) that are loadedat the start of the C sourcecode.For the previousexample,the prototypeis asfollows: Subloutsin€Ndne

(ty9€

Var1,

...

)t

Personally,I put subroutinesand functions above the mainline to avoid the need for protot)?es. The only time I useprototypesis if I havepreviouslycompiled the subroutine or function and I'm linking them with the mainline.In thesecases, I will load them all in a .h include file. One important reasonto place subroutines and functions before the mainline is to avoid the bother of maintaining the prototypes if the functions themselveschange.If you changethe input or output parametersof a function and do not changethe prototype.you will get an error message.

11 q

;., tt)

...)

r-ts Funclion

statelreats

return ,

dn

ReturnvaLue

tud.

//

h€r€ i

h3

subroutia€s

To invoke a function, a statementin the following format canbe used: 1=

FunctiotiNam€ ( inlrutParanat€r,

...)t

I trl

Or a subroutineinvocationcanbe used: e"a gubloutineName

( inputPalam€ler

,

.. .)t

/-!

If a functionis invokedasa subroutine,then the return value is ignored upon return. To demonstratethe operation of a function in a program,I createdcFactoral.c, which calculatesthe factoralsof the first eightintegers: #inclual€ - Calculale cEactoral.c /* Inlegera Thia 10.

Plogram

Calculatses

lh6

Factorala

Factorals

of

fldr

1 to

nr *"{

p,

{n 1.,

int tnt

Faclval,u€i

int

Facloral(

f,or

//

F

Ft

j.nE Nt|rib€r)

(Faclvalu€ Faclvalu€

!€tur|r ,

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rrl|ke D:.eflko 04.09.15

(

$r.

r{

= 1r N\jlib€r > 1t N\rntber-- ) * lludberi = lactvaLu€

.+

EactvaLu€i

,r. H

ElLd Factoral

TE

nain( )

{

SectionFour C L a n g ua g e F e a t u n e s

t3

69

for

(i

j

,

-

1r i

<= Ir

= FactoraL

i++)

//

Return the Factoral of 1 t o 8

(i) t

while(1 =- 1), E^d. cEactoral //

The programmultipliesthe integerby eachdecrementingvaluesuntil it reachesone.Thisis not the traditional way of calculatingfactorals.In C, this function is normallyshownasan exampleof a recursivefunction. I will not be discussing recursivefunctionsin this book for two reasons:(1) It is beyondthe scopeof this

book. and (2) the PIC16F684microcontrollercannot suppot it easily. When you simulatecFactoral.c, I suggestyou display the Watchwindowfor the four variablesusedin the program:i, j, FactValue,and Number.When you run the program,you will noticethat eachof the four vadables,exceptfor Number,is displayedat all times. Unlessexecutionis within the Factoralfunction.the "Out of Scope."The variableNumber hasthe message, reasonsfor this messagewill be explainedin the next exDerlment.

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( int

i.nU Plinecheck

value)

t j

fo'. li i++) if

j)r

In C, you havethe ability to redefinevariablenames, so long asthey are declaredwithin functionsand subroutinesand not outsidethe main statement.This feature is known as/ocal variablesand allowsyou to reuse commonvariablenames(suchasi, j, k, and n) without fear that the contentsof a variablewill be changedor corruptedby other functionsand subroutinesin the application.To demonstratethis capability,I created the programcPrime.c,which hasthe function PrimeCheckthat usesthe samevariablesasthe mainline uses.Whenyou run the applicationandtry to monitor the valuesfor the counterand flags(i andj, respectivelyin eachfunction),you will discoverthat MPLAB IDE hastrouble monitoringthe correctvalue for the variablesand may evenstop single-stepping correctly! #include - Find cPrine.c /r Integers

Che Primea

in

the

first

200

This Prograr works through each of th€ prime rumbera frorn 1to 200 anal indicates which ones are prine h,t att€lpting bo divide every integer fron 2 to ( (Nurlb€r / 2) + 1).

= 1;

)

{ int

i,

for

the

MPLAB

(0 == (va1ue % i))

= 0;

jt

(i

= 1r i <= 2OOi i++)

j = Primecheck(i) i

//

rf

DiviEible

//

value iE NOT Prime

//

Retuln the Prime Fl.ag

//

T6at Every

//

i:::::"'= l+nrar

is

)

(1 == 1)r whil6 E ral cPrirne //

//

t if

i

P].ime

Loop For€ver

The problemsare causedby the confusionthe MPLAB IDE simulatorhasregardingwhichi or j it shouldbe displaying.This doesn'tmeanthe program isn't working properly,but that MPLAB IDE cannot properlydisplaythe valuesof i andj. In this programthe i andj local variablesthat are specificto eachfunctionare uniqueto one anotheras well asto any variablesthat are declaredoutsideall the functionsof the program.Thevariablesthat are

l , a 3 P I C @l l C l J E x o e r i m e n t s f o r

under

/

jt

70

run

< ( (vatue

main( )

is

to

(i

ead. Plinecheck

//

Thia program rDE simulator On1Y.

alegigrteal

= 2,

j letuln

aaBume lhe value ia prime 2) + 1)) && (0 != //

the Evi I

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declaredoutsideall the functionsare known asglobal within any function. variablesandthey canbe accessed When debuggingfunctions,you will probablywant to changethe variablesthat are local to the functioninto globalsso that you can debugthem usingthe full featuresof the MPLAB IDE simulator.From a programa bad ming qualityperspective, this is not necessarily idea;by testingand debuggingindividualfunctions beforeintegratingthem into an application,you to ensurethat they are correctbeforethey are usedand simplifyyour applicationdebug. The big questionyou are probablyaskingyourself from this experimentis "When shouldI uselocalversusglobalvariables?"When I programin C for the PC, I try to make all my variableslocal;but I useglobal across variablesonlv for the valuesthat are accessed

the applicationand/orthat would becomecumbersomeif their parametersneedto be passedto other functions.I do not follow this rule when I am programming the PIC@microcontroller,becausethe PICi6F684processorarchitecturedoesnot allow for parameterstringsof unlimitedlengthto be implementedefficiently.Ideally,you shouldkeepyour input and output parametersto 16bits.Additionally,there couldbe situationswheremultiple variableswith the samenameare declaredbut only very rarely accessed, and thereforetheremay neverbe any dangerof them appearingmultiple Iimesit nestedsubroutines(snbroutinesandfunctionsthat otherscall or are calledby other subroutinesor functions).For thesereasons,I tend to declareall the variablesasglobals,exceptfor counters(i,j, and so on) and temporaryvalues.

Experiment26-Defines and Macros

In Section2,whenI introducedyou to variabledeclarations,I alsonotedthat constantnumericvaluescould be declaredaswell.Theconstantvaluesthat wererepresentedby the labelswould be substitutedin anytime the label wasencountered. In this way,commonlyused values could be stored asan easy-to-rememconstant readability of the prostring that should help the ber gram.I did not focuson the constantvaluedeclaration. I try to avoidusingit in my programming,becauseI believethat its declarationcanbe easilyconfusedwith variabledeclarationsand becauseit doesnot encompassall the differenttypesof data that are usedin programming. To declareconstantvaluesof all types,I usethe #definedirectivebuilt into the C programminglanguage.The format for the #definedirectiveis as follows: *define

labeJ. t (Argumert,

...

)I

Strinsl

with the label encountered, the .slrilrgthat is associated is insertedinto the program.A subtlebut very important differenceexistsbetweenthe two, asI will showin this experiment. The stringreturnedby the definelabel doesnot haveto be numericonly;it canbe alphabeticcharactersor evenC programlanguagestatementslike if or for. Thesesubstitutionsare allowedbecausethe define substitutionstake placein the compiler'spreprocessor. That is,the stringsare substitutedinto the program sourcecodebeforecompilationstarts. Further enhancingthe usabilityof the #definedirective is the ability to specifyparameterstrings(the argumentsin the previousdirectivedescription).These parameterstringsare substitutedin the #definestring, allowingyou to customizethe stringfor a particularsituation.Theadditionof parameterstringsallowsthe #delineto behaveasa macroand allowsyou to easily enhancethe operationof your application. Macros are seclionsof code that are commonly used,but deemedinappropriateastheir own subroutinesor functions.In this expedment'sdemonstration application,cDefine.c,I showhow #definesare usedto definea constantvalueaswell as,with smallpiecesof code,to providesimplefunctionsthat may be required multiple timesin an application.It isn't unusualto refer to constantvalues,declaredby usingthe #define directiveand codestringsthat are addedto the applical\on asmacros.

When a label that has been declared as a constant is encountered, the numeric value associatedwith the label is returned.When a label declared in a #define is

5ection Four C L an g u a g e F e a t u r e s

7L

#incLuale - Denonstrate cDefia€ /* fo! Equales anal Maclos The C "Defin€' equaling values Th€ae proglall.

the

Defin€

Dir€ctive

direclive can be useal fo! aa weLI as Droviding basic

caDabiLiti€s

are

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Halalware Nolea: PIC15F684 running al 4 M$z ln ReBet iE li6al ali!€cE1y to vcc PrograEniag Haralware

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both maclo thig

Sinulato! via PuLluD/

Myke Pletlko 04.09.26

tors;wh€nthesecharactersare encountered,the preprocessormovesthe next line to the end of the current one.This allows for multiple-line macros or for situations like this, where you could cram the macro string all onto one line.But by usingthe line continuance character,the line canbe readmore easily.Secondly, the macro has a question mark (?) and a colon (:) characterinsertedinto it, neitherof which seemto make any sense. The questionmark and colon are part of an altemative conditionalexecutionstatement.which hasthe following forrn: Conalltq)reBBion FaIB€E apr6ssion

F4

rl

{q3

| / Deelneg constantva].ue *t[€fine ldgbByt€

*alefine

Lowtsyte(value)

va].ue

/

vaLue

% 0x0100

uDDercase (charact€r) *alefine \ ( (Chafactse! >E ra') && (Chalacler Clraract€r Charact€!

0x0100

<= '2,))

?\

qL!

nain(

)

iat lilurbell , N\nber2 t char Char1, Cha!2, Cha!3t Nunb€r1

= 0x0123t

//

Iilr,mber2 = ConBtantvaluot

.r{

Chart

ft!

//

= '1"

//

(Nlrnber2 ) r

//

t I I

Nllriberl

= IJowBt't.e (Nurber2

),

//

rtr f.i nl )

N a!

Get Bigh Byle of, Nunb€r2 eel Lolr EyEe of Number2

cha!1

= UlrDercase ( Charl. ) ,

//

ISBE "qpD€rcaaen

char2

= UrpDetlcas€ (Cha!2 ) ,

//

llac!o only value be Changetl

Chal3

= UDDelCade (Cha!3 ) i

$hi1e

(1 == ].)t

i\*

. *,{

Stantlaral rnitlalize LnLEiaLi,ze witsh Define Characte! hirializ€

Cbar2 = 'b', Char3 = '7" lituIl|ber1 = HighByte

//

lf

( CoaalE:rDles s ion ) i = TrueE qrressioni €Ise i = FalseE
Personally, I do not like usingthis alternativeform of the if statementexceptin macros,asits operationis not alwaysobvious(e.g.,the colon canbe easilymissed or misreadasa semicolon),it doesnot allow rnultiple conditionallyexecutingstatements, it is not logically nestedwith other statementqand it often endsup running over a singleline,which makesits operationeven more cryptic. It is,however,an efficient way of adding a conditionaloperationto a macro,just asI havedone in this experiment.

{ ,it

tso

Before ending,I shouldnote that the #definedirective canbe usedfor renamingI/O pins in PIC MCU applications. Ratherthan accessing an I/O pin asthe genericlabel,you can assigna label to it usingthe #define directive. For example,if you had an LED wired to RC2, you could declare it using the following statement: *al€f,ine

//

:

When "CondExpression"is evaluatedif it is true (not zero,which is what "true" means),then "TiueEx"FalseExpression" pression"is evaluated;else is evaluated.Thisstatementis usefulfor situationswhereyou want to seta variableto a specificvalue,asin the code:

0x1234

(valu€)

*tlefine

? Tru€E:qrr€BEion

FiniEhetl, Loop Fo!6ve!

Enal cDefiDe

The strangeformat of the Uppercase macro will requiresomeexplanation.The two backslashes at the end of the first two linesare line continuanceindica-

LED RC2

Now, when the PICC Lite compiler encountersit, it replaceseveryinstanceof"LED" with "RCZ."This is a usefultrick for makingyour applicationseasierto read andwrite.

&'&4 4.6 trt

72

l , e 3 P I C @l l C l J E x p e r i n e n t s f o n t h e E v i l

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Experiment ?7-Variable Flrrags

X

€

Array addressingis a common feature of most programming languagesand provides you with a mechanism to allow you arbitrary variable data within your application.Array addressing could alsobe called indexedaddressing,and it utilizes an arithmetic value to specifya certainvariableelementin an arrayvariable.Arrays allow you to handle more data than could be handled normally in an application and to write applications that would be very difficult without this capability. Using arraysin your program is actually quite easy. In Figure4-1,I showhow I visualizean array-as a seriesof memory elementsthat are given a single variablename.Eachelementis accessed by specifyingan indexvalue.The indexcanbe a constant,a variable,or an arithmetic expression.For example,eachof the threestatementsbelowwill load the variablei with the contentsof the fourth elementofArravVariable: i

-

i

= Arrawariabl€ljl

Arlayvariable

[3] ,

// //

r

E.presEion

int

= t' = 3

-

Arratryarlablel(l

177. L2L, LOi,

Tenp

= gortArlay

SortsAffaylil

= SoltArrayli

+ 1l

sav€ !h€ eurrent Valu€ // store Next value ia Current // Ilul Ortgl.aal currents value in Next //

[i]. + 1lt

= Te pt

Thesethree statements,which require an extra Temp variable, are a fast and efficient way of swapping the contentsof two variables,not just arrayvariable elements.

fll?J,[!*z: s a @rs "Bubble" Testind ArrayElement Values

Declared As: inl

VariabfeNane[4];

Figure q-l

Array

Figure U-2

\ArrowsShow Exchange of Sort

Bubblesort

SectionFour C L a n g ua ge F e a t u n e s

tt\ lv l.t

l-" tn

x

tg {

IT

LOLI i

A commonprogramusedto demonstratethe operation of arraysis the bubblesort (seeFtgure4-2).In this simpleprogram,eachelementof an arrayis read and comparedto the onenext to it (this is the bubble).If one elementis greaterthan the next,then the two are swappedusingthis simplethree-statement sequence:

sortelrayli

Intlex is a Constanl rnd€x is a

i = arrawariabl€ Ij * 1r, ,, rtiJ"'**ff jt

Array elementsin C start at an index of zerq not one asyou might expect.You couldcreateyour programswith one extra element and start your index at one,but this would not follow conventionalC programrning and would make it difficult for others to read your program. I should point out that many other languages(including various flavors of BASIC) all have their fust array element aszero,so this is a convention that is transferable to other languages. To define an array variable, the variable with its sametype is specifiedalongwith the numberof elements of the array.Along with this, the initial valuesof the array can be optionally specifiedby placing them within bracesasI show in the samplearray variable declarationstatementshownhere:

73

sr-i F.

p,

tr

F

{D

F

h1 H

p,

m

The mostbasicbubblesort programthat I cancome up with is asfollows: #incLudle - siry)Ie cbsoft.c /* This values.

Proglarr

ia

C Plogram

a aimple

Bubblo

'Bubbl€

So!t.

of

ffi

Ii

to

run

in

the

)

== 1)t

//

Firriahotlloop

d{il )

{ * r?a

a

* f-* .

3,

4,

ll

o, 2, 4,

6,

A,

//

9,

L2,

//

L5r,

//

o're Row Tvo Ront 'I}rte.e Row Eolr]. Row

i = 3r Proaluct

i = {t = MuLArray IiI

tilt

i, - 4t Product

i = 3i = MulArlay

til

tilt

i = oi Proaluct

i = 2i = MuLAl.lay ti]

tilt

i = li Proaluct

i = 2i = MuLArray IiI

til;

whir.e(1 == 1)t

whiL€(1

{ :

zer o

(

(t = 0r i < siz€of ( So:.tvalues ) t i++) for - (i + 1))t (J = 0r i < (sizeof(Sorlvalues) fo! j++) (sortvaluestjl > Sortvaluea [j + 1]) { if TdE) = sortvalues tj I . = Sorlvaluealj + 1lt Sortvaluealjl + 1l = ledlpt sorlvaluealj , // f5-

'at

//

rnaia ( )

t

F-{

0,

o, 1, 2,

20

iltt i, j, TenD, char Sorlvalu€E [20] ={33. 5{, 42, l2O, 37, 5, 99, 105,8.2r, 1OO,33, 4r, 77, 41, 69, t3,86, 51, 901t

&'"{

0,

o , 4 , a , !2,

Earflware Not€E: ThiE Progiam haa b€en written IIPLAB IDE Sillulalor ONIJY.

nair(

0, 0,

Rolt

Sort

l[yke gretlko 0{.08.03

P1

inl i, j, Produclt ints I'lutArray [ 5 ] I51 = t0,

//

Edil

cbsoll

So far I havediscussed single-dimensional arrays (arrayswith one index),but you can alsoimplement multidimensional arrays in C by simply adding a second setof squarebracketsasI do in the following exampleprogram.Note that when I cameup with the initial values,I kept the valuestogetheraccordingto the row in which they appear. *inc].ual€ l* clIulArlay. c - UultiDle

Dimen6ionaL Array

This Program alemoaEtslates how e two alimenaional array coulal be inpldEntsetl !'luttiplication. sinptify

to

myke pretlko 0{.09.0? Haralware Notes: ThLa Program haa been wrilten to the llPLAl IDE Simulato! ONLY.

{1} &,{"t

74

run

in

l

//

Ertd. cMulAffay

If you are looking at the cMulArray program,you might think that it is a clever way to avoid having to use a complex multiplication routine. Unfortunately, when the compiler is calculating the address,the row index (or the first dimension) is multiplied by five and then addedto the columnindex (or the seconddimension) to calculatethe indexelementto be accessed. Another way of putting this is that all arraysare actually singledimensional,and the multidimensional array format is simply provided as a way to avoid requiringthe programmerto calculatethe address. Before using a multidimensional anay, think about how necessaryit is to your application.Two- and threedimensionalarrayscan use a lot of spacethat could be usedfor other functions.For the cMulArray program, the MulArray variable takesup 50 bytes (five rows timesfive columnstimestwo bytesfor eachintegerelement). If we were to extend it to three dimensiongthe total memory requirementswould become250bytes, which is much more than is availableto the application. From an academicperspective, the bubblesort algorithm is probablythe leastefficientalgorithmfor sorting data.Other sortingmethodsare much more efficient, but they require resourcesthat are generally not availablein the PIC MCU processorarchitecture, and implementing them can be quite difficult. In any case,for mostPIC MCU applications, the bubblesort is good enough;in fact for the rest of this chapter,I will look at different ways of implementing it using different C languagefeatures.

l , a 3 P I C @l l C l JE x p e n i m e n t s f o n t h e E v i I

Genius

Experiment 28-Structures and Unions and personalinformation.Thestructuredeclared below is an exampleof somethingthat couldbe used bv a storeto keeDtrack of its customers: Cualodnellnfo struct { char Nalne [ 6{ ] t char Aalalless [ 128] t int sonePh[101t int

When processingdata or handlingmultiple datatypes, simplearraysare often not the answerto the problem. What is neededis someway of combiningmultiple piecesof disparatedatain the samevariable.Therewill alsobe caseswheresinglepiecesof data may be dividedin differentwaysfor differentdatagroups.The solutionto this problemis actuallyquite elegant.In the C languageyou candefineyour own variabletypes with specificparameters; you evenhavethe ability to representdata in more than one way. Tt1estruct lqngu(tgestatementts used,to define a variableof arbitrarytype that cancontainmultiple piecesof data.Theformat of the statementis:

// // //

BusPh t10l ,

//

char ernail [32 ] t CDate !astSalet

//

int

//

LastsameAmtt

Custon€r Nane Aalalres s Ilortre Phone Nunbe! nork Phone Nudber Date of, Last saL€ Anounts of, Last sal.e

When usingthe structstatement,the StructureNameand StructureVariable parametersare optional (althoughboth cannotbe missingat the sametime). StructureNameis usedasthe type for other variables:

With this information,a storecan find out who its bestcustomersare,who the mostrecentcustomersare, or the storecanquery other parameters. Oncethe storehasfound the parameterinformationit wants,it hasall the other personalinformationimmediately availablein the structure.In Customerlnfo,note that I usethe previouslydefinedstructCDate asa type of one of the variablesin the struct;you can imbed structs into other structs.Thisis an effectiveway to make your applicationeasierto read andwork with. In the previousexample,you might be thinking that the structurecould easilybe built for a singlecustomer, but how would it work for multiple customers?Like numberscan be built into arrays,so can structures.For example,if a storehad 2,000customers, an arrayof Customerlnfowith 2,000elementscould be defined usingthe statement:

Structsurertc'e

cuslomerlnfo

SlructureName st'ruct ctype valiab1e1Na$et ctyp€ valiable2Namet

I

(

siructurevariaure;

Variablet

Structuresare initializedin declarationstatements in the sameway arraysare initialized,with valuesbeing appliedto the appropriatevariablewithin the structure in the sameorder asthe structureis declared: StructureTEe Variable VariabLe2Namevalue.. .)t

[2000] t

In the followingprogram,I havedefineda 20-element anay of a structurein which a valueand the initial arraypositionare storedand then sortedusingthe samebubblesort methodthat wasusedin the previous experiment:

{Variabl€1Naneva1ue,

Finally,variableswithin a structureare accessed by connectingthem to the structurenamewith a period as in the followingstatement: SturctureName.variablelNane

CustonerDatabaae

= 47t

As I saidat the start of the experiment,structures allow multiple piecesof data to be includedtogether.A typicalapplicationcouldbe in a databaselistingnames

#incluale cBtrctsort.c /t Bubble Sort

-

Structure

This Program is a sinple 20 Values uBing a'I array

Baseal C Ploglam

"Bubble of

so!t' Struceures

of

nyke preilko 0{ .08.03 Eartlware NoteB: This Program has been wlitten the MPr,ar rDE simuLator oNLY.

Section Four C L a n g u a g e F e a t u r e s

to

run

in

unsigneal i. jt ={33, 5{, 42, L2O, 37, 5, char hitvalueal2o] 99, 105,8,21, 100,33, 41.,77, AL, 69, L3, 46. 51' 90)t strucb Datagtruct { unsigneal ltritPos, char valuei Te$)t ) SorlAl.layt2ol,

//

Datastruct

T€lnpt

Sorts Position

//

Initial

//

20 El€ment Structure Asray TenDorery Value aa strjucture

//

nain ( )

t t l

for (i = 0t i < 6izeof (hitvalues), = i; soltArray I i ] . rnitPos = Inilvalues .value SorlAffaylil til iof ll ,

L'J , t"{

lJ rrq

(i - 0t i < aizeof for !!€ru) = SortAllay Ii I t wbiLe(1 \

{ J

$

{

//

== 1)t

( Inl.tvaluea)

//

FiniEh€dloop

lowHigh

atruct

L5 Bi.t- value Bit valu€a

I/

8

aa two

Lt Hi

char char

unl.on

(

//

{

lonlligh int it ) tr,

variabl€ as 8 Bit valuea

16 Bil

2x

or

bt

Normally, when you are reading and writing the full 16 bits,you would definethe integern asfollows:

t

(1 = 0r i < aiz€of (Initvalues), i++) for - (i + 1))t for (i = 0r i < (sizeof(rui|alues) j++) (sorlArrayljl.value + > soltArlaytj if 1l .value) { Terfr = SortArlay [j I t = sortarraylj + 1lt sortAlrayljl + 1l = l'€tw|i SortAlfaylj ll fi l

b"ri

'r'"c

i++)

the samememorylocation.For example,if you had a 16-bitvariable(ctypeint) and wantedto accesseach byte individuallyasseparatebltes or togetherasa 16bit integer, you could define a structure breaking up and a union as:

r i++)

Fo!€ver

n.i

= 123{5,

s al'e !6

ll

Bit

value

iu

'n"

To accessthe individual bytes of n, you could use the followingstatements: Bylevariabl€ Bytevariable

= n.b.Ht = n.b.Lt

which seemvery cumbersome, but they are equivalent and often much more efficiently implemented than thesestatements:

ErLd. cstlclsort

In cstrctsort,note that I treat the entirestructure like a simplevariableand copy it in the samemanner as I would with a simple variable.This feature helps to keep the complexity of an application to a minimum. Therewill be timesthat you will want to sharedata in a structure (or accessit asif it were a different variable).This is done usrngthe union stqtemenl.The union statementhasthe samesyntaxasthe structstatement andproducesa new datatype.But insteadof each valuewithin the union beingunique,eachis locatedat

Bylevariabl€

= n.i

/

255i

//

By!€variabl€

= n.i

4 256:'

//

Return the High Blrt€ of "n" Return the Low B1.t€ of "n" aa uodulo 255

Structuresand unions are not programming tools thal you will usea greatdealto programmicrocontrollersin C; they are usuallyrequiredfor large-system programming.Despite the apparent lack of applicability, they are useful tools and keeping them in the back more oI yourmindcouldmakeyour programming efficientor easierto read and follow.

29-Pointers and Lists Experiment Two programming conceptsseemto strike terror in the heartsof computersciencestudents:working with pointers and working with lists.The conceptsthemselvesare not terribly difficult to understand,but implementing them in a prograrn and debuggingthe program can be difficult and frustrating; so difficult and frustrating, in fact, that many people question their understandingof the concepts.Philosophically,using

F

t {

nt b*4 t.4 l - I

76

l,e3 PICo llCu Exoeriments fon the Evil

Genius

pointersin programsis curently out of favor.For example,JavaandMsual Basicare designedto hide the operationof datapointers.But in C, understanding the basicsof pointersis criticalto understandinghow to manipulatecharacterstrings.Lists are generally considered a "mainframe"compulerprogramming conceptfor handlinglargeamountsof data,but they do havesomeusefulpropertiesthat you may want to considerin microcontrollerapplications. If you wereto guessthal a pointer is a variablethat pointsto the locationof a data object (vadable,struct, or union),you would be correct.Like other variables, pointersare typed,with the asterisk/splat character(+) usedin the declarationafter the type to indicatethat the variableis a pointer to a specifictype of data.For example,a pointer to an integerwould be declaredas: intr

IntegerPoint€!i

DecLar€ Pointer

//

an Integ€r

The ampersand(&) characteris usedto indicatethe addressof a variable.Tostorethe addressof a variable in IntegerPointer, the followingstatementwould be used: = &it

IntegerPointe!

//

IntegerPointer points to =variable <\#3{>.i<\*34>

The valuein the variableindicatedby the pointer canbe accessed by placingan asterisk/splat in front of the variablein a statement.In both of the following statements, the contentsof the integeri (whichis pointedto by IntegerPointerusingthe previousstatement) are incremented. i = i + 1, *IntegerPoj,nter

= *Int,egetpointer

+ 1t

When pointersare usedwith structures,the values withinthe slruclures areaccessed by usingan arrow madeup of a dashand a greaterthan sign ( ->. ) insteadof the simpledot,or period,of a structvariable.Creatinga structvariablewith a pointer to it and assigninga valuewithin the structureusingthe pointer would be accomplished usingthe followingstatements: struct in! int

PixelPoint

{

//

Pixel

information

xt yt

) PointvaLue; Pi.xelPointr

DtrPixel

ptrPixelt

= &Pointvaluer

//

//

Pointer to inf,orma!iod Point to Structure

Pir{€l structure

the pixeL Vari.abl"e

DtlllPixel->x

= xPositiont

AaBigtL a VaLue to lhe "X" coordlinate

//

Pointersand pointersto strucluresare often usedas parametersto functions.By passinga pointer rather than a value,the originalvaluecanbe changedand much lessdata canbe transferred,resultingin faster programexecutionand smallervariablememory requirements. This is really everythingthereis to know about pointers-in conceptthey are quite simpleand easyto understand.Debuggingprogramsusingpointersis generallydifficult becausefew simulatorsand emulators providepointer informationin any kind of meaningful context(suchaswhich variablethey are pointingto). To effectivelydebuga programthat has pointersin it, two thingsare required:a goodunderstandingof how variablesare stored(and where,most likely,they are in the variablememory)and some imaginationin trying to understandhow the code works.In the next experiment,I will showhow pointersare usedwith charactersand strings,but for now you know all the basicsand probablymore than you will needfor the foreseeable future. Lisl.rconsistof structureswith pointers,which point to the structurebuilt into them.They allow each instanceof the structdata type to point to another instanceand to form a linearchainof structs.Thetwo lypesof listsmoslcommonlyusedin programming (seeFigure4-3) are singlylinked listsand doubly linked lists.The advantageof the doubly linked list is that it allowsmovementin eitherdirectioneasily,while the singlylinked list allowsmovementin only one direction.The end of the listsare usuallymarkedwith a null (value0) or -1. Other waysexistfor organizing structures. For this expedment,I wantedto sort the sameselection of numbersasusedin the previoustwo experiments.Here we will usea singlylinked list.The code itself,which follows,is not muchmore complexthan the codeof the previousexperiments, but I experienceda numberof challengesdebuggingand confirming the application'soperationthat would make this experimentunreasonablydifficult for an inexperiencedprogrammer. *incluale cpstrctsort.c /* BubbLe Sor!

-

Structure

This Program is a simple pointerB 20 values using S!ructurea rryke predko 04.08.03 tlalabrare Notes: This Proglaft has

been

5ection Four C L a n g ua g e F e a t u r e s

Baaed C Progran

"Bubble to

writtelr

go!t"

a Irink€al

to

run

of tist

of

in

7'l

Curren!

l:lrffi Doublv

,

--l T--.

while(l

l-.-__-l ,

ListPointers

th€

Lists

MPITAS IDE Sinulator

ONLY.

it unsigrlefl char hitvalues I20l ={33. 54. 42, r2O' 37' 5, 41, 69, 13, 45, 99, 105, 8, 21, 4OO, 33, 4L,71, 51, 90) t atruct sErucl char

(

Datastruct Dataslruct*

N€xtDr

//

hitElementt

//

ehar vaLuet ) SortA!ray[20],

Slartr

//

gointe! to the Next Element Initial Elenent

20 Ele';nerft Structure Afray/S!art

Previousi

//

C1ftte':t,

//

Enalinqr

//

Pleviou€ Pointer vaLue Pointe! Current value Poinler to the LaEt Elemenl

main ( )

t Start.Ner{ED

// fr

Enaling = Currentt , / / eralrw

iiii""ffi Figure q-3

= current->NextsDt

= &SortArraytolr//

Point start IJist < sizeof (Initvalues) r .NextD = &SortAlrayti+1] = ii . hitELem€nt .value = hitvalueE [il

(i = 0r i for SoltAllayIi1 soltA].lay [i] soltArlaytil // '.of J SortArray t 19I . N€xtD = (structs Endling = SortArlay[19],NextDt

to of

//

//

== 1);

Move Bach

//

the

FiniBhealEooP

Pointer

Forever

EtLd. cpEtrctsott

Although buildingthe singlylinked list is quite simple and can be found in the first for loop,sortingthe list by movingpointersis not exactlyobvious.In order to sort the list,I usedthe Previouspointer asan anchor to the list and then movedthe pointersasshownin Figure4-4.When I developedthe code,I madea diagramsimilarto Figure4-4 to make surethat I understoodhow the pointersweremovingthe two list elementsasin the bubblesort swap.Despitemaking this diagram,it wasstill a challengeto get the program to work properly.I endedup makinga spreadsheet with everyelementand eachpointer and kept track of how they changedandwherethey endedup pointing. Overall,writing and debuggingthis applicationtook me aboutfour hours,whereasthe other sort applications presentedtook Iessthan an hour. The puryoseof this experimentis to demonstrate how pointerscan be easilycreatedand point to different piecesof data.Lists are generallybestsuitedfor largeapplicationswith many data elementsthat might be reordered.inserted.or deletedat random.At first glancelistsmay not seemto be appropdatefor microcontrollerapplications, but there are caseswherethey are useful,suchasallowingeasyeditingof a robot programsequence. I suggestyou considerthe list concept whenyou havea situationwhereadding,removing, andmovingdata elementsis required.

the the

i++) t

(

P.evaous

t

Datastruct*)

-1,

Previous

]tr'hiIe (start.NextD = &sEatEt Previous

!= Endins) t of, to lhe Start // Poinl the Liat = Start.NextDr Current // Point lo the First ElernenE (current.->NextD lrhile != Enaling) - >NextD- >value ) { (Current->value > culrent if = Culrent->llextDt Previoua->NextD = Culrent->NextD->NextDt Currenl->NexlD Pr€viou6- >NextD- >NextsD = Cutrent, = Previoua->NextD; Previous Nothing Changeal, Goto lilext // ) 61ae { = Currenti Previous

78

Ial

Previous Current Previous P€vious.>NonD> NenO =

Figure Q-Q

P I C @l l C l JE x p e r i m e n t s f o r

List sort

the Evil

Genius

ExFeriment 30-fharacter 5trings char*

Ne$rName1, Ne$rl{ame1

NewNane2

t

= lilyNalnei

- &M]'Nametol;" NerdNane2

Although working with structsand unionscanbe difficult,working with pointersand characterstringsreferencedby pointersis quite easyif you follow the basic conventionsoutlinedhere.Unlike other languages (suchasBASIC), C doesnot nativelyhandlestringsof data.Although it canhandleindividualASCII characters,which are treatedlike eighfbit numbers,each ASCII characteris storedin an arrayelementto create a characterstdng.Toeasethe workload causedby copyingeachcharactereachtime it is used,the starting addressof arrayscontainingASCII characterstringsis normallyusedto referencethe entire string.These methodologiescombineto make working with character stringsin C more complexthan in other languages you may haveusedwhenlearningprogramming.The sameattributesandmethodologiesmake character stringsmuchmore efficientwhenyou are comfortable working with them. When a numberofASCII charactersare combined in a string,they normallyend with a null (zero)character to form what is known asan'ASCIIZ strins."The p l a c e m e no lf t h en u l lc h a r a c t eart t h ee n do [ t h es t r i n g is automaticwhenit is enclosedin doublequoteslike this: char

Mtalame t121

= nq'ke

predlkotr r

//

Def.i')e

a

;;-;;.--*' To declareenoughspacefor the stringand the null characterat the end,you will haveto count the number of expectedcharactersof the stringand add one to it. When a stringvariableis referenced,it is referenced by the vadablenameandit is a pointer to the first characterin the variablearray.

== ilflilil:l

Eachindividualcharacterin a stringis accessed as an arrayelement.IndividualASCII characterscan eitherbe representedasdecimal,binary,or hex numbersor the actualcharactersin singlequotes.In the following codesnippet,the third characterof MyName is comparedagainstupper case'K'.

// //

(NevNar$elt2l == rK' ) if Stalements executeal if Equal to Uppelcase elae .K, Sla!€llrents ex€cuted if Not l4)pelcase

rK,

Along with decimalrepresentations ofASCII charactersand the actualASCII charactersin singlequotes, a numberof specialcharacters(precededby a backslash[\]) are alsoavailablein C.Thesecan be placed eitherin singlequotesasa singlecharacteror aspart of a stringlistedin Table4-3 and found in the "For Consideration"pafi of this section. Dependingon the circumstanceq ASCII stringscan be locatedin eitherprogrammemoryof variablememory.To allow the compilerto differentiatewhich is which,the "constkeyword" shouldbe put beforethe charin the pointer declaration: const

cha!+

ConstPointeri

The constkeywordwill make the pointer 16 bits long (insteadof the standardeightbits,which can accessonly variablememory).The extrabits are used to indicatethe locationof the pointer data aswell as the locationwithin the specifiedmemory.My rule of thumb regardingthe useof the constkeywordis to let the compilerindicatewhenit is needed;mostof the time it is not required. To demonstratehow stringsof charactersare implementedand manipulatedasarraysof singlecharacters, I havemodifiedthe sort programto sort an aray of pointersto strings.I createdthe stdngCompareand stringcopyfunctions,which perform byte-by-byte operationson the bytesin the strings,becauseC does not havethis built-in ability.

5ection Four C L a n g u a g e F e a t u r e s

79

#include cslrIlsolt.c /*

sifiD1e

Bubble

C Program

(i = 0r i < 10, t++) fo! for (j = 0r j < (10 - (t + 1))r j++) gortvaluea (atringcdE a!€ ( (char*) lf [j], (cha!r) + 1l) > 0) { soltvaluestj SortVaIu€B [jl ) t stringcoDy(TenD, + 1l)t atrinqcolDr(SorlvaLuea [J L Sor|alu€stj ( Sorlvalu€e !!eq>) t sEringcopy [J + 1]' // EL I

Solt

"Eubble Sortd of ThiB Proglam is a simple 10 Fou! chalecter Stsringa b!'moving them functions iD the solt arlay. fhe atring w€re wrilten bY Myk6 Pr€alko. nvhe pretlko 0{.08.05

!'hi1e

Earatware Not€B: Tlris Program hag b€en !h€ I.IPITAB IDE Simulator

u! St l-{

"r{ H

?n

jt unsigled i, sorlvalu€a char* char T€alI) [5] t cha! nameo [5] cha! name]. [5] char nam€2 [5] char name3 [5] cha! nam€{ [5] char names [5] char nrme6[5] char nam€? [5] cha! nameg [5] cha! nameg [5] int

F.{

| writlen ONIY.

to

run

E c = = = = = = = =

Etllngcorq)a:.e

( char*

{

slringl,

//

chat*

gt!lng2)

cd|tr)are two Strl.aga

i n t j = 0 ,

(i = 0r ('\0' l= Sttiusl.lil ) && i++) - strins2til, j - stsltnsltil // j < 0 ff, S!!ing]. // j = 0 if stringl. // ) > 0 if strins2

for

4J t! ru p"{

ru "Li F \

return ,

//

Striag].t0! for (i stlingltil ,

ll

Return

1,

he

< string2 = string2 > st':.ing2

t SorlveLuea [0] Sortvaluea [1] Sortvalues [2] sortvaluea [3I Sortvalu€s [{I sortvalu€s [5] sortvalueB [5] so!tsva1u6a [7] gollvalueB [8] sortvaluea [9]

= = = = = = = = = =

nam€ot na.nelt aame2, narne3, n€$€4t nane5 t nam€5t nam€7t nam€8t nam€gt

Errd. cEtlmgort

*incLudla cstrDsolt.c /*

sil[I,le

c Program

Bubble

So!t" llhis Proglem la a ai!E)1€ "Bubble with novlng 10 Four Cha:.actse! Stringa atrings.

lilotea: llartlwar€ Progran has b€en l|rl'!t€n fliis o$[Y. "n" ** IDE Sirmrlator

stringl

Byte

to

*,

char* charr cha! cha! cha! cha! cha! cha! char char char char

SoltvaLuea TettE)i narreo t5j = nenel [5] = n€me2 [5] = neme3 [5] = neltr€{ [5] = = nene5[5] . name6[5] Dame? [5] = '1ame8 I5l 5 name9 [5] =

[10] t "mtk6"t ntoDin' 'lolin' trcalarri njune" n lf'tlntr ' ulrar1rn' "ryra"' trsara'r "kira"

P*

&€4 80

Fo!€ver

sorl of

!vk6 Dr€alko 04.08.0{

= String2 [0] r // Cor4, E}l.e t.ilsl .\0, - 1lt i++) != Stringlli = sErins2 [i],

E!.d. stringco9y

FinisheauJoop

In the programyou'll seethat I first initialized arraysfor eachnameand then passedthe addressof eachnameto the SortValuesvariable.In standardC, you could initialize a pointer variableto a seriesof double quotedASCIIZ strings,but this is not possible in the PICC Lite compiler.I suspectthat the reason why it's not possibleis due to the memory organization of the PIC MCU; the initial valuesare storedin programmemory,which is completelyseparatefrom the variablememory.Before a variablepointer can be assignedto a value,the value must be storedin a variable. After writing cstrmsort,I noticedthat I could improve the performanceof the sort routine by simply movingthe pointersto the stringsin the sort instead This programis of copyingthe stringsthemselves. listedhere:

ConrDare ReEull

cha!* strl.ng2) stsfing1, into I / coDy stltng2

nain ( )

#

(0 == j),

E'l'd atlingcotDpale

EEringcoDy(clEr* I

iI

Cry

//

j;

//

in

[10] t trnvketr, trtonLn' trLofi" trcaren' trjulent n].r.ann' n$aryn' ilr\ylent trsalan' nkiren'

//

( 1 == 1) t

1 , 2 3 P I C @l l C U E x p e r i m e n t s f o n t h e E v i l

6enius

run

in

lnl |

(ctla!*

alringcorq)are

Stringl, char* // contr'ale two

String2) slllngs

for

i n t j = 0 , for (i = 0, ('\0, !- srrinslttl j - slrinsltll - strins2lilt // i < 0 if // j = 0 tf //j>Oi-ES r€lurn

!!aid(

t++1

strinsl < Sl!1ngl2 = String2 strinsl t r i n g 2 > String2

R€tsutn CdlDare Result

Eird. slringcon[)are

//

I

//

Jr

) && (0 == i ) ;

unaigneal

i,

Sorwalues Solwaluea Soltvaluea Soltvaluea goltvaLua3 goltvalueE gortvalueE Soltvaluea Soltvalues Sortvalu€a

jt [0] [1] [2] [3] [{l [5] [6] [7] [8] [9]

= = = = = = = = = =

= 0r i < 10r i++) (i = 0r i < (10 - (t + 1))r i++) (Btringcompa!€ ( (chalr) if Sortvalues (char*) Soltvalu€s tj + 1l) > 0) T€d|D = Sortvaluea [j I. = Sortvalueslj Sortvaluealjl + 1]t gorlvalues [j + 11 = TerD; | // fi

whiL€(1

ll

!

== 1)t

//

Finiah€alt

tJ 1, (

nam€o t nalne].t name2 t nane3t nalle4t narlesi aam65i nar€? t aameSt aame9i

. . . . .

m lt:

{*

ooD Eorev€r

t-J "

ErLd cstrpsort

The updatedversionof this sort is recommended and demonstratesthe important functions of pointers that you shouldbe comfortablewith in order to program in C.To recap,thesefunctions include the followrng:

)

t

(t for

Declaringpointers Assigningpointersto the start of variable stnngs Accessing(readingand writing) pointer values Defining ASCIIZ strings AccessingspecificcharactersinASCIIZ strings as array elements

d\

r*d

r t i

t-l

r*" 9,, ! i F

Experiment 31-LibrargFundions

tsd

t"/ with strcmp and strcopy,respectively,and added the string.hheaderto get the following: *inclutl€ #iaclutl€ - SirE)le cstrf,Sorl.c /*

q F"t

C Program

Bubble

sort ! d

nBubbl€ Sortn of Ihis Program ia a siq)Le 10 Four Chal.acle! SlringE blr noving them in lhe soll array. CdE)arison anal litovemeDts ar€ provial€al by l"ibrary Funclions.

In the previous experiment, I showedyou how to compare and copy eachbyte in an ASCIIZ variable array. Klowing how to create thesefunctions in C is important,but it is not alwaysnecessary for mostapplications.As part of the C languagespecification,you can take advantageof a collection of functions that will take someof the load off you when you are programming.Thesefunctions (along with the PICC Lite compiler C languagestatement definition) are included in the "For Consideration"part of this sectionand are part of the "C run-time" library that is linked with your application at run time. For example,I replaced the stringcompare and the stringcopy functions in the previous experiment's code

X

llyk€ prealko 04.08.05 Harflware Noles ! ThiE Progr€m has been th€ MPLAB IDE ginulato!

j, u.Eaig!€d i, char* SortvaLu€s char TerDIr[5] t char nameo [51 char nam€1[5] = char name2 [5] = chat nam€3 [5I E char nam€4 [5I char nan€5 t5l = = char !€.ne5l5l

Fr.

wrilt€n to ONLY.

run

in

[10 ] t "!oni" nlorinr ncaran'june"t nltrnntr "nar't'".

SectionFour C L a n g ua g e F e a t u r e s

dI

- '4yran t = rrsaratr t = "kira",

narLet [51 nameS [5] name9 [5]

cha! cllar char

For Eonsideration

nain ( )

(

Sortvaluea sortvalueE sorwalu€a sortsvaluea sortsvalu€a Sorlvaluea soltvalu€s So:atvelu€s Sortvalu€a Sortvaluea

[0] I1l [2 ] [3] [{l [5] [6] [7] [8] [9]

= = = = = = = = = =

nameot 'rameli name2t naltre3t nalle4 t namest name5t !a!re7 t lr€lneSt aame9t

for (i = 0r i < 10r I++) for (j = 0t j < (10 - (i + 1))t j++) (sllclE)( (char* ) Sorlvalues ljl, if (chai*) Sorlvalues tj + 1l) > 0) ( Sortsvaluea [j I ), strcDy(T€dlp, strcDy(Sortvalu€a tj + 1] ), [j L Sortvaluea strcpy ( sortvalu€a t j + 11, Teqr) t ll fi | !thile(1 |

l, .,-t P EIJ

t+

at l.Lt

ls

"*t r,J 3*t

//

== 1),

//

Fini

ahefltJoop

Foreve!

EE.d. cal:.fsofl

The resulting program takes up just about asmuch spaceasthe previous one and runs in roughly the same amount of time, which meansthat my routines are similar in efficiency to the provided library routines.The big difference is that the first program was shorter and required lesseffort to debug.(I assumethat the strcmp and strcpy functions work properly and this assumption is extendedto all the built-in functions of the runtime library.)For the mostpart, I would recommend that the run{ime library functions are usedin your C programswhereverpossible. One caveatexiststo the previous statementand that is the linker brings in only the library functions that are calledby the application.Ifa functionis not called,then the function is not linked into the final application hex file. I'm pointing this out becausein you canvery quickly smalldevices,likethe PIC16F684, use up all of your available spacewith libraries and applicationcode.It is importantto rememberto balancethe number of built-in and user-written functions so you don't useup the programmemoryavailableto your application.

f l

H

For modern systemgC is the programming languageof choicebecauseit is availablefor a wide rangeof systems and processors(including the PIC microcontroller). This ubiquity requires anyone who is planning on developingan application for processingsystemsto have at least a passingknowledge of the language.The following information is specific to the HT-Soft PICC (including the PICC Lite) compiler: Application mainline/entry point is the main function: nain( ) // ADpltcaEton {

Coile

|

// ll

!

Codle

N)plication

E'rd ApDllcatiorr

Functions are defined in a similar forrnat to the main function: Frnctlon( R€turn_Ttz9e Parameter. . J) stsalt. { // nrdctioa .

// leEuln

|

TtT)e Paramet€r

//

zunction

T]ZI)e

Coal€

valuei

EnA l\tnction

The function can be placed before or after the mdn function(not inside),but if it is placedafterward,there must be a function prototype, like this one,before main: Retu!n_T!'D€ l,lractl.on( Paramete!..1),

llyl)e

Peraneter

[,

lPt pe

PIC MCU configurationregisterfusevaluescanbe specifiedusing the "_CONFIG(x)" define (found in the pic.h include file). The specifiedvaluesare ANDed together to form a complete configuation register value. I recommend that a value for eachbit be specified to ensureproper operation of the microcontroller. Table 4-1 lists the PIC16F684'sconfiguration fuse bits, the HT-Soft defined constant'soption values,the AND valueq aswell asthe Microchip defined assemblylanguageconstantsI havenoted alsorecommendedvalueswhen I felt it wasimDortant.

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Data declarationsare very consistent,starting with the constant declaration: coaat inr tJabel = value, ., vanaDtesoeclaredInstdea Iuncfion(rncludlngthe main vaiable) are known as local variables,are accessibleonly within that function,and may be different upon entry into the function. Variables declared outside of all functions are termed,global, as they can be read and updated anywherein the application.

where the last characteris an ASCII null (0x{00). Array dimensionsmustbe specifiedin the variable declaration statement.Multidimensional arrays are defined with eachdimension separatelyidentified in squarebrackets([ and]): int rb'eeDspac€ [Din1l tDn!21t pointers are declaredwith the asterisk (*) character after the variable type: char*

tlzp€

rra.t€l

o rt

o o 5

u f-r.

glrinq'

p-

t= valu€l,

Valueis an optional initialization constant.The different types are listed in Table 4-2,with the data value rangesare in parenthesis. Single dimensional arraysare declared using the form:

qt

o

Finding the addressof the pointer in memory is accompliJred using the ampersand(&) character:

rj 9' cF

EtsringAda!= &strins,

,J.

ll'I)e Labeltsizet

[= { hitialization

o

values..}lt

5

Strings are defined assingle dimensionalASCIIZ uuTays: char

striDgl

17 I

= "I'his

is

a gtridg"t

Table 4-1 PIE'l6F58qConfiguratlonFuse Values Connguration Bit

PICEUte CompllerValue

Microchlp Value

Ualue-Functlon

Bit 11-FCME\ Fail-Safe clock Monitor Enable FCMEN (Default), FCDIS (Recommend)

_FCMEN_oN -FCMEN_oFF

0X03FFF,0X037FF

Bit 1o-IESO,Intemal Extemal switchover

_IEso_oN

0X03FFF,0r03BFF

Bit 9|8-BODEN, Blownout DerectEnable 0x03DFF,0x03CFF

IESoEN (Default),IESoDIS

(Recommend)

_IEso_oFF

BOREN (Default),BOREN_XSLP, SBOREN,BORDIS

_BOD-ON _BOD_NSLEEB _BoD_sBoDE\_BoD_oFF

0X03FFF,0X03EFF.

Bit 7-CPD, Data Memory Protect

UNPROTECI (Defaulr/Rec), CPD

_CPD_OFF,_CPD_ON

0X03FFF,0X03F?F

Bit 6- _CP, Program Memory Protect

UNPROTECT (Default), PROTECI

_CP_OFF,_CP_ON

0X03FFR0{3FBF

Bit 5-MCLRE, Extemal _MCLR Pin Enable

MCLREN (Default), MCLRDIS

_MCLRE_O\

0X03FFR0X03FDF

Bit 4-_PWRTE, Power Up Timer Enable

PWRTDIS (Default), PWRTEN (Recommend)

,PWRTE_OFF, _PWRTE-ON

0x03FFR0rt3FEF

Bit 3-WDTE,Watchdog Timer Enable

WDTEN (Default), WDTDIS (Recorffnend)

_WDT_O\

0X03FFF,0x03FF7

RCCLK (Default), RCIO, INTCLK, INTIO (Recommend), EC, HS, XT, Lp

_EXTRC, _EXTRCIO, _INTOSq _INTOSCIq _EC_OSC,_HS_OSq _XT_OSq _LP_OSC

Bit 2:0-FOSC, Oscillator Selection

_MCLRE_OFF

_WDT_OFF

S e c t i o nF o u r C L a n g u a g e F e a t u n e s

0X03FFF.0I{3FFE. 0X03FFD,0X03FFC, 0X03FFB,0X03FFA, 0x03FF9,0x03FF8

83

Table4-3 C BackElash Eharacterg

Table4-2 PICELlte EomDilerBata TgFeg Tcpe

Btt Size Comments

bit

1

BooleanValue

8

lnteger (-128to ASCII Character/Signed

char

unsignedchar 8 short

16

unsignedshort 16

rn)

Eharacter

nSC Value

FunEtion

\0

00x00

Null Character

0x007

Alert/Bell

0x008

Backspace

0x009

HorizontalTab

0x00A

New Line (Line Feed)

0x00B

Vertical Tab

0x00C

Form Feed(New Page)

0x00D

Cariage Retum

0x05C

ASCII BackslashCharacter

0x03F

ASCII QuestionMark

0x027

SingleQuote

0x022

Double Quote

\b

unsigned Integer (0 to 255) 6'7) SignedInteger ( - 32,768to 32.'7 UnsignedInteger (0 to 65,536)

int

16

SignedInteger (-32,768 to 32J67);sameas short

unsignedint

16

as UnsignedInteger (0 to 65,535);same unsignedshort

long

to SignedInteger ( 2,147,483,648 2,147483,647)

unsignedlong

UnsignedInteger (0 to 4294,96'l,295)

float

assume3 digitsof Real (0 to 1/-6.81(1033); accuracy/defaultfloating point mode

double

assume 6 digitsof Real(0 to l/-6.81(10'3): usingPICL -D32 compiaccuracy/specilied lation option

\f

\?

Mathematical operatorsinclude the ternary operator and thoseshownin Table4-4 andTable4-5. The ternary operator is the form: TestE
Calculatingthe addressof a specificelementin a string is accomplishedusing the ampersand(&) characterand a stringarrayelement: Strinssterts

= &Striagtnl,

The variable'stype canbe overridden,or cast,by placing the new tlpe in front of the variable in brackets: ( long)

'r{ fta

tl q,

StrtngAaLl!

= 0rr0123450000t

The C assignmentstatementis in the following format: variable

= E:lplesEioat

variablevalues,or Expressionscanbe constants, mathematicalstatementsin the format:

(J

'd

o r l

or Constantscanbe decimal,binary,hexadecimal, ASCII charactersenclosedin single quotes.Table 4-3 liststhe specialbackslashcharactersthat canbe placed in single quotes so they lvill be evaluatedassingle Note that a singlebackslashcharacteris characters. interpr€tedasa line continuance.

$4 w f:.t

and executesin the following manner: ifTestExp is not zero,then Expl is evaluated.IfTestExp is equalto zero,then Exp2 is evaluated. The binary operatorslisted in Table 4-4 can be simplified to the modified equalsstatementif the destination variable is one of the parametersof the expression. Table4-6 liststhe resultingcompoundassignment statements C decisionstructuresincludethe ifstatement, if

(E qr!€sBion)

{ // Ex€cut€ ) ela€ ( // Ex€cut€

[(..1

if

&q)reEaion

ia

no!

if

E qtlession

ia

zelo

( "f,als€"

(E .preEsion)

t // ,

E:tecute whil€ eLlhv ll

E)q)toaaion

i€

aot

zero

("true')

and the for statement, fo!

( initialization,

LooD

E:.DresBioni

{ Execute

!"hile

ltt€

E:rpleasion

is

not

)

84

)

the while statement, while

[(..1 variable I Constant topelator variable I colEtsant I[)..1]

: E
? E:gt1

l , e 3 P I C @I ' l C UE x p e n i m e n t s f o n t h e E v i l

6enius

Increment zero

)

Table4-4 E Binarg0peratorg

Table 4-5 C lJnarg Operatol-s

Dpepto, Pnonry Flltctio?

Operator Function

*

r )

Highest Multiplication

2'sComplement negation

Division

"/"

!

Logicalnegation(Return zero if valueis not zero and retum not zero ifvalue is equalto zero)

{

Addition

<

Bitwisenegation

S

Subtraction

11

Incrementvariablea_f?rexpressionevaluarionif on the vadable'sright-handside;incrementvariable

fs ;

Modulus

+

Shift Left

belbluexpression evah",i."ii"" irt" r".i"ilr" rlr,

Shift Right

handside)

I€ss-thancomparison(Return not zero if true,zeroif false)

Decrementva ablearel expressionevaluationif on the variable'sright-handside;decrementvaiiable beloreexpressiirevaluationifon the variable'sleft-

Less-thanor equalscomparison(Return not zero if true,zero iffalse)

Lowest

) while

f}J 1 {S t{

creater-than (Returnnotzero comparison if true,zero if false) (Rerurnnolzeroi[ Fquafs-to comparison true,zeroif false)

Table 4-6 E Eompound Fssignment Statement Bperators

r|

Operatot

Function

NoFequals-to (Retumnotzero comparison

O S-{ **

&:

BitwiseAND

if true,zero iffalse)

:

BitwiseOR

BitwiseAND

^

BitwiseXOR

+:

Add to Destination

BitwiseOR

Subtractftom destination

LogicalAND

Multiply destination

LogicalOR

l= '/.=

Divide destination Divide destinationand return modulus

Intheforstatement,multipleinitializationandloop>> incrementstatementsare separatedby commas. Puttingin multiple initializationsand incrementstatements can make your applications difficult to follow To executeconditionally accordingto a value,the whenyou are first programmingin C.To avoidthis switchstatementis used: extra complexity,I recorrmend that you stick to just havinga singleinitialization and loopincremenlwhen "**:lj:T:i::1""' ' you first usethe for statement. trE:q)ression"== nvaluetr " *fi:::*;i For loopinguntil a conditionis true.the doiwhile statementis used: ,, ,r";i3'i!i""' sratsementss are rru€ ato t // Executs€until

m

ru

itwiseXOR &&

#

$*,

-

(Return ,'iT:il:|?1"::;Hii:,:i3iarison

&

LJ

l the E qrression iE zero (',fal6e")

Finally, the goto Label statement is used tojump to

a specificaddress:

(E:{Dression),

To jump out of a currentlyexecutingloop.a break statementis used.Thecontinuestatementskipsover remainingcodein a loop andjumpsdirectlyto the loop condition(for usewith while,for, and do/while loops).

soco r'abeLt Labet:

5 e c t i o nF o u r C L a n g u a ge F e a t u n e s

85

&J.

To return a value from a function, the return statement is used: retuln

Stat€m€ati

Directives are executedat compilation time and usedto modify th€ sourcecode for the application and

Table 4-7 E Directives Functian

Directlve

Null directive;do nothing. #assertCondition

Force an ellor if condition is false.

tasm

Indicate the start of inJine assembly.

#endasm

Indicate end of inline assembly.

#defineLabel (Optional Define a label that will be replaced with the specified text when it is Paramete$) Text encountered.If optionalparameters are specified,instancesof them h the text will be replacedby the parameteN specifiedwhen the label is invoked.

o

"'.{

#undefLabel

Delete the definedlabel.

#line Number ListFile

Specifythe line numberand file name Ior listing.

#include

Load the specified file found in the INCLUDE folder path.

*include"File"

Load the specified file by fi$t looking in the cudent folder and then in the INCLUDE folder path.

#error Text

Forcea compilereror (stopcompilation) and output text for error information.

#warningText

Forcea compilerwarningand output text for waming information.

#if Condition

If the condition is true, passfollowing code to next #else,#elif,or #endii

#ifdef Label

Ifthe label hasbeendefined,then pass followingcodeto next #else,#elif,or #endii

JJ

|6 g 0,

t

CI

o

If the label hasnot beendefined,then passfollowing code to next #else,#elil or #endii

#ifndef Label

This directive is an else/if, and the con" dition is testedonly ifthe previousif directive is not true.

#elif Condition

#else

Invert passfollowingcodestatus.

#endif

End a +tif,#ifdeI, #ifndef, #elif, or #else condition.

#pragmaString ke).tords

Passthe specifiedstring to the compiler (seeThble44).

t'l

are listed in Table 4-7.Each directive is given its own continuesonto the next line by line and,if necessary, useof the backslash(\) character. The PICC Lite compiler pragma options are used by the compiler to changeits operation and are listed in Table 4-8.Note that for the code presentedin this book, these options are not requfued. In the PICC Lite compiler manual, you can find additional information, including error and warning descriptiong information on including assemblylanguageprogramming in C applications,and file format referenceinformation that is not critical to performing the experimentsin this book but may be useful to you. I have not included the list of PICC Lite compiler options in this section becauseyou should be able to successfullyrun the PICC Lite compiler under MPLAB IDE without having to changeany of the operating parameter$ In Thble 4-9, I have provided a cursory list of the library functions that are available in the PICC Lite compiler. I have arrangedthe functions by alphabetical order within the include file rather than by overall alphabeticalorder, asthis should make it easierto find specificand related functions.Unless otherwise specified. assumethat the label is for a function. For more information, you should consult with the PICC Lite compler User'sGulde (available for download at www.ht-soft.com),the .h files in the PICC Lite compiler INCLUDE folder,and standardtextson the C programming language.

Table 4-8 FlvailablePIEELite EompllerPragmaEirectives Pragma OireEtive

Function

interrupllevel 1

Allow interupt functions to be called by main line code.

Jis

characterhanEnableJIS (Japanese) dling in strings,

Nojis

Disable JIS character handling in strings(defaultcondition).

p ntf_check(printf) const Use printf formattingconventionsfor string checking. psect text = newpsecrname Change the object file psect name. regusedRegisters

Specify registers that are used in interruPt handler'

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Table 4-9 PIECLite CompilerLibraruFunctionsand Macrog Library Functlon

Description

conio.h Bitkbhit(void);

Skeleton of keyboard hit function

ctype.h int isalnum(charc)

Macro testing if c is alphanumeric

pic.h

rl

o

int isalpha(charc)

Macro testing if c is alphabetic

int isascii(char c)

Macro testing for seven-bit value

int iscntrl(char c)

Macro testing for ASCII control character

int isdigit(char c)

Macro testing for ASCII decimal digit

itrt islower(char c)

Macro testing for ASCII a through z

int ispdnt(char c)

Macro testing for p nting character

int isgraph(char c)

Macro testing for nonblank printing character

inr iennn.r/.h,r.\

Macro testilg for nonalphanumeric character

int isspace(charc)

Macro testing for space,tab, or newline

int isupper(char c)

Macro testing for ASCII A thrcugh Z

int isxdigit(char c)

Macro testidg for ASCII hex digit

int toupper(int c)

Macro to convertASCII characterto uppercasb

Ft g, ct

int tolo{er(int c)

Macro to conveit ASCII character to lowercase

P.

int toascii(intc)

Macro to ensure parameter is valid ASCIImath.h

double acos(double f):

Retum the arc-cosinein radians of the input value

doubleasin(doublef);

Retum the arc-sine in radians of the input value

double atan(double f);

Retum the arc-tangent in mdians of the input value

doubleatan2(doublef doublex)i

Retum the arc-tangent in radians of the input value

doubleceil(doublef);

Retum smallestwhole number not lessthan f

doublecos(doublea);

Retum the cosine of the radiatr argument

double cosh(double f);

Retum hyperbolic cosine for argument

double eval-poly(double x, const double* d, iDt tr);

Evaluate the polynomial with coefficients stored in array d at point x

double exp(double f);

Retum the value of er

double fabs(double f);

Retum the absolute value of f

doublefloor(double0;

Retum largest whole trumber not lessthan f

double ftexp(double f, int* p);

Brea.l(real number into integer and fraction

double ldexp(double I int x);

Integer is added to real and result retumed

double log(double f);

Retum natural logarithm of f

double log1o(double l);

Retum base 10 logadthm of f

doublemodf(doublef, double* iptr);

Split f into integer and ftaction parts with same value as f

doublepow(doublef, doublep);

l(etum t'

double sin(double f);

Retum sine of the mdia! argument

doublesinh(doublef);

Retum hyperbolic sine for argument

doublesqrt(doublef);

Retum the squarercot ofthe argument

doubletan(doublef);

Retum tan of the radian argument

double tatrh(double f);

Retum hyperbolic tangent for argument

di(void);

Disable intedupts

o p

a F, p-

o

o Ft

eeprom_write(unsigned char addr, unsigned char value); Store the specified byte at the specified addressin the PIC MCU's data memory

stdio.h

ei(void);

Enable interrupts

unsigned char eeprom_read(unsignedchar addr);

Return the byte at the specified addrcssin the PIC MCU'S data memory

unsigned char pdntf(const char* f, . . . );

Standard C print routile; before using sdtout must be defined for application

unsigned char sprintf(char* buf, const char* f, . . . );

Convert C pdntf fomat parametels to stdng at buf

unsignedxtoi(constchar* s);

ConvertASCII hexadecimalstring to integer

S e c t i o nF o u r C L a n g u a g e F e a t u r e s

87

Tabfe 4-9 (continued.) Librara Function

Description

stdlib.h int abs(intj);

Retum the absolutevalue (positive)of the input

doubleatof(constchar* s);

ConvertASCII string to doublevariabletype

int atoi(constchar+s);

ConvertASCII string to integervariabletype

long atol(constchar* s);

aonvert ASCII string to long variabletype

div_t div(int num,int divisor);

Divide and return quotient and remainder

ldiv t ldiv (long num,long d);

Divide and return quotient and remainder

int rand(void);

Retum random number fto/JJ0 to 32,767

void srand(unsigned int seed);

Initialize random numbergenerator

string.h constvoid* memchr(constvoid* block,int val,size_tn); Searchstringfor specificbyte

\J ,"* JY{

time.h

k dt ,.{I l .J

int memcmp(constvoid* sl,const void* s2,size_tn);

Comparetwo blocksof memory

void* memcpy(void*d, void* s,size t n);

Copy n bytesof data betweenpointers

void* memmove(void*s1,constvoid* s2,size_tn);

Copy n bytesunder all circumstances

void* memset(void*s,int c, size_tn);

Fill block ofmemory with specifiedcharacter

char+strcat(char+sl,const char* s2);

Concatenates2 at the end of s1

char* strchr(constchar* s,int c);

Searchstringfor first occuffenceof c

chaf strichr(constchar* s,int c);

Searchstringfor first occufienceof c in upper-or lowercase

int strcmp(constchar* sl, constchar* s2);

Comparetwo strings

int stricmp(constchar* sl, constchar* s2);

Comparetwo stringswithout regardto upper-or lowetcase

char* strcpy(char*sl,const char* s2);

Copy s2into buffer (characteraray) pointedto by sl

char* strcspn(const char* s1,constchar* s2)t

Find numberofcharactelsfrom the start of s1to the part ofthe string that matchess2

size_tstrlen(constchar* s); (char* s1,constchar*s2,size-t n);

Find the lengthof the ASCII stringchar*strncat Concatenaten charactersfrom s2onto the end of s1

int strncmp(constchar* s1,constchar* s2,size_tn);

Comparetwo stdngsfor up to n characters

int strnicmp(constchar* s1,constchar* s2,size tn);

Comparetwo st ngsfor up to n chamcterswithout regardto upper-or lowelcase

char* strncpy(char*sl,const char* s2,size_tn);

Copy n charactersfrom s2 to s1

constchar+strbrk(constchar+sl,const char* s2);

Return a pointer to the lirst instanceofs2 in sl

constchar* strrchr(char+s,int c);

Searchfor characterstartingat the end of the string,rather than ftom the front

size_tstmpn(constchar'r'sl,constchar s2);

Retum the lengthof s1,startingftom the start that containscharacters rrom sz

constchar* strstr(constchar* s1,constchar* s2);

Find the first occurrenceof s2in s1

constchar* stristr(constchar* s1,constchar* s2);

Find the first occurrenceofs2 in sl without regardto upper-or lowercase

char* strtok(char*sl,const char+s2);

Break s1into a seriesof tokens,separatedby s2

char* asctime(struct tm* t);

Convertthe variableofthe tm struct type into an ASCIIZ string

char* ctime(time_t*t);

Converttime in secondsto ASCII string

structtm* gmtime(time_t+ t);

Break down time into type tm

structtm* localtime(time_t*t);

Break down time into type tm

time_t time(time_t*t);

Skeletonoftime read function

{l} T '

t l

t{ 0 88

l , E 3 P I C o l ' l C UE x o e r i m e n t s f o r

the Evil

6enius

Section

Five

Plfl SFEBqMicroctrntrol ler Built-inFunctions

Ptc16F584 tlt31? adjustable age legulator in package Io-LED balg.aph

voltTO-220 dispLay

REd LED Creen

LED

100C)!esistor 330!) res istor 4?0O 10-pin

DMM NeedIe-nose

plie!s 10k breadboald mountable potentj.ometer

Breadboard Wiling

ki.t

Jeweler's

les istor

1 lk bleadboard potentj.omete!

sclewdriver

mountable

2 0.01 pF capacitols 1 Breadboard-mountable Jrur swrEcn (!--5vr1!cIl 8G1903 recomnended)

A big question askedby software developersis whether or not to rewrite an application.The reasons for doing a rewrite are usually good and noble; the author may havefigured out or leamed waysthe application could be mademore efficient, new hardware may be availablethat makesthe task easier,or there may be too many potential errors in the software that only a complete rewrite of the codewill prevent problems in the future. Pcrsonally,I am of the opinion that applicationsshould never be rewritten unlessa tangible reasonexists The question,"what will happen if the changesare not implemented?" hasto be asked,and unlessthe answerincludessomethingabout cost savings (e.g.,the application could be usedin a cheaper nricrocontroller), then the rewrite should not be attempted.This may seemlike an off-topic way to introduce a sectionabout the builfilr featuresof the PIC16F684,but it is surpdsingly relevant becausemany of the builfin featuresof the PIC@MCU introduced in this sectionreplacesoftware functions that you may have written to imDlementdifferent function*

1 9-vol.t

batte.y

1 g-volt

battery

1 Three-cell cl ip

pack

AA battely

3 AA battelies I

Two-cell AA o! AAA battely pack

2 AA o!

AAA batteries

The builfin featues of the PIC MCU can make your applicationa /ot smaller,easierto write,and easier to debug.For example,in Section 3, I introduced an application that displayedan incrementing binary value on the eight LEDS of the PICkitrM 1 starter kit. It did so by sequencingtbrough eachof the LEDs simultaneouslyto give the impressionthat they were all on continuously,when in fact no more than one

89

LED was on at any given time. I feel that the code was fairly clumsy and unnecessarilylong.The length made it very difficult to follow valuesfrom top to bottom, and assuch errors had a good chanceto make their way into the different statementsof eachgroup of statementswritten to optionally tum on an LED.

U,.

, j

r ! l

f

0.4

'.l

&E r t taEr

D0-D7

of

aE a!

"CPKLED.C" aa a bas€, cycl€ each lhrough Using LED6). LED at 100r( p€r Eecondl (1250 ua betw€er lrhLch ia rewrilten i6 th€ geconil v€rsion fhiB lo leAuce the amounl of Arrays take aalvanleg€ b!| th€ aDplicatsiolr. space lequireal

to of

tni'k€ Drealko 0,r.09.12

& IID|TDIS & PI{RTEN & IICIJRDIS COIAIE(IN'IIO IINPROIECT \ & IJNPROTECT & BORDIS & IESODIS FCMDIS ) ,

& &

qrl

k{ qs r€ f l H

= 0, in! value int Dlay = 65i // LED Tine on DelaY variable cofls! char PoRTAvalue [8] = {0b010000, 0b100000, 0b010000.0b000100, 0b100000,0b000100, 0b000100,0b000010], 0b001111, coasts cbar TRISAvalue tgl = {0b001111, 0b101011,0b101011, 0b011011,0b011011, 0b111001' 0b111001) t const char NOIPORTAI8I = (0, 0, 0, 0, 0, 0, 0, 0', nain

()

t

I!

F

EORTA = 0, Cl'tCONo = 7t AI{SEL = 0,

ll //

Tlt!'j T)n

j

//

ReE€l

//

I,oop Foreve!

= 0;

while(1

== 1)

off ol.t the

conltalatola atlc DisDLaY

counte!

{

.*{

f o r ( i = 0 r i < 8 r i + + ) Each of th€ I / / Loog through | (n = 0t n < D1ayt n++)i for ( (vaIue & (1 << i)) == 0) lf PORTA = NqIPoRTAIil,

?-

t:r{

IJEDS

+ 1r

//

Inerdl€nt !/ 2s

lh€

Counler

(J >= s0)

| ) I /

value=va1ue+1i

//

j = 0; // ti

//

// E'ld

61ih!t clEDDiaD

DisDLaY Incldlent Counter Reset the couDter

2

This applicationtakesup lessthan half of the space of the original (both in terms of lines of code and instructions required), although it usesonly four more variable b1'tes.By just about any measurement,this rewdte is substantiallybetter than the original, but still I would consider replacing the original with it only if the application required more program memory than was available.Therefore, you should keep the knowledge regarding using an array to implement the multiple LED display code in the back of your mind until you have to implement a similar function. The built-in hardware featues of the PIC16F684 provides similar opportunities when you are looking over working applications.As you first start programming, you will implement basic input and output functions using the standard digital I/O capabilities of the microcontroller pins.Thesefunctions will simplify generating motor control signals,help you processanalog data, and help you more easily communicate with other devices.Although thesebuilt-in features will seemdauntingly complex in the beginning,they will becomeeasierasyou becomemore familiar with developingapplicationsfor them. I can promiseyou that you \ryilllook back and consider rewiting the applications to take advantageof the hardware "behind the pins."But remembermy advice:You should rewrite this code only if there is a concrete reason for doing so. Of course,you can avoid the whole question of whether or not to rewrite to take advantageof hardware featuresby implementing the features in your application right from the start. In this section,I introduce the different built-in functions of the PIC16F684 alongwith somesampleapplicationsthat illustrate how thev work and what can be done with them.

g

# (-) at {,*

90

€very

{

I

,tl

= j

if

In Section4,I showedyou arrays,and you might have thought about using them to rewrite the CLEDDisp.c application. I have done this and listed the programhere: #incluale CLEDDiED 2.c - 2trd velaiorr /* increm€nt ing counter

€la€ PORTA = PORTAvalus I i I t TRISA = TRISAVaIUe lil t // tof

l , P 3 P I C o l ' l C l JE x p e r i m e n t s f o r

the Evil

6enius

frt

Experiment 32-BrournoutFleset

X {}

1 Prc15F684 1 1M317 adjustable

t

voltTO-220

age lelfulato! package

in

1k bleadboald

mountable

;3

(D

:

l

Potentiometer REd LED L

Gleen LED

1 330C) l/4-vratt

1 0.01 p"F capacitor tYpe)

DMM sclewdriver Jekeler's lk potentiomete!)

(for

(any

{^J }'.l t I

B!eadboa!d-mountable (E-Sr{itch SPDT switch 8G1903 lecoaunended)

Needle-nose pliers B!eadboa!d WiliDg

resisto!

k j.t

g-volt

batterY

g-volt

battery

I H

pack

L"' In a previous experiment I explained that when I first started working with the PIC MCU and writing about it, various specializedcircuitry would have to be added to provide reset with brownout protection for the application.The PIC16F684, like other recently releasedchips,hasthesefeatures built into it, allowing you to take advantageof these featureswithout adding to the cost or complexity of your circuitry. Unfortunately,you may find that the work required to add the advancedreset functions to your application code is not trivial. In this experiment,I will demonstratehow the brownout detect and reset circuitry built into the PIC16F684works andprovideyou with somecluesas to how to decipherthe datasheets when a hardware functiondoesn'twork. The PIC16F684is designedto work in the voltage rangeof 2.0 volts to 5.5volts,which makesit ideal for battery power without a voltage regulator.When the voltagegoesbelow2.0volts,the PIC MCU can no longer operate reliably, it may stop,it may run different parts of the program memory,or it may executethe instructions incorrectly.To help avoid theseproblems the brownoutreset(BOR) canbe enabledin the configurationfusesto detectlow voltageconditionsand enablethe PIC MCU'S reset. To demonstratethe operationof the PIC16F84's brownoutreset,I createdthe test b/ownoutdetect(or

BOD) circuit shown in Figure 5-1.This circuit usesa power supply(basedon the LM317 variable-voltage chip) to reducethe operatingvoltagefrom 5 volts (nominal)down to 1.25volts.Note that eventhoughI am using the brownout detect reset function of the PIC MCU, I did not enable the MCLR function of RA3. The LM317 (seeFigure5-2) is a nice little adjustablelinear voltage regulator circuit that is ideally suited for a task like powering the PIC16F684in this ckcuit to test its brownout detect function. The lower end of the chip'soutput is 1.25,and the upper end is definedby the V'" power source.Its output is defined by the formula: V*r=1.25vx

(1 +

(R2lR1)) +

i$ssdxR2

Ptc16F684

_-a: ._ I

Figure5-l

Section F i v e P f C l , t F E A ql ' il c r o c o n t r o l l e r

BOD circuit

BuiIt-in

Functions

91.

pt

H

(0

BasicCircuit

.) LM317 Label

Adjust

V.

Figure5-?

il". LM3l7

but, asIo,r,is only 100u.A,the productof it timesR2 is normallynegligible.This is why in Figure5-2,I have the simplifiedformula.For thisapplication,Iuseda 1k potentiomcterfor R2 and a 3300 resistorfor Rl; this givesme an output voltagerangeof 1.25volts to 5.00 volts when a g-volt batteryis usedfor application power.Thesmallsizeof the breadboard-mountable 1k potentiometer meantthat I hadto usea jeweler's screwdrivcrto changethe potentiometer(whichcan be seenin my prototypewiring in Figure5-3). The plan wasto havethe PIC16F6U4 light the green LED on RC3 after reset,but if the resetwascausedby a voltagebrownout,thc red LED on RC2 would be lit. Thc originalapplicationcodewasbasedon cReset.cin whichthe _BOD bit (knownasBOD in PICCLitefM compiler)of PCON wasset after power up.Along with settingandcheckingthis bit, the BOREN label, insteadof the typicalBORDIS label,wasusedin the configuralionfusespecification.

I shouldpoint out that a numberof different optionsexistfor brownoutreset,includingignoring brownoutresetduringsleep(or low-power)modeand allowingbrownoutresetto be controlledby application software.Also, a numberof bits are setin the factory.which will tune the actualbrownout resetvoltage. For this application,I avoidedthe more complex brownoutresetoptions,wantingsimply to staywith a hardwareresetwhenthe voltagebecametoo low. With this setup,the red LED alwayslit on power up,regardlessof the voltageinput and whetheror not I setor resetBOD on power up.Additionally,I tried different configurationregistervalues-all with no success.Untbrtunatelythe useof the brownout resetin the Microchipdatasheets, or apnotes,is not shownand a Googlesearchdid not revealany codethat usesthis feature.As I scouredthe datasheets. I noticeda differencein hov{the PCON registerbits were specifiedfor power up.For the BOD bit, in one caseit wasmarked as"unknown" insteadof 0 at reset.which meantthat for it to havea valid valueafter a brownoutreset,it would haveto be set manually.With this information in hand,I then recodedthe cBOD.c applicationso that it would first checkfor a power on reset,at which time it wouldsetthe BOD bit.And on subsequent resets, the stateof the BOD would be checked. #include cBOD.c - Monitor /*

Reaet

o l r Bfown

Out

This Program !vi11 light an r,ED baseil ( Powe! Up or Browtt out ) nras reset Polrer Suppliedl to the PIc16F681l LM317 wired to proviale 1.5 to

Det€ct

on how it

comes fron 5 Volts

an

LEDS are connecteal to: RC3 - Power Up Reset RC2 - Brown Out Res€t myke predko 04.11. L0

& WDTDIS & P!\IRTEN & MCI,RDIS & -CON!'IG(INTIO I'NPROTECT \ & UIIPROTECE & BOREN & IESODIS & FCMDIS)t // <- Note "BOREN" nain(

)

t PORTC = 0i Cl,lCONo = 7 t / / .r\arn off Comparator6 ANSEL = 0t / / Flrrn of f ADc T R I S C = 0 b 0 0 0 1 1 0 0 1 1 t // RC3:RC2 as Outputs if

(0 == PoR)

//

Power-on

POR = 1r BOD = 1r Rc3 = 1r

// ll //

rrralicate Powe! Active Make suf€ BoD se! r,ED Set Polrer uplcood

Reset

occulred

t Figure 5-3 ctrcLutry

9Z

Assembled broytnout detect experiment

I if

l , e l P I C @f l C U E x o e r i m e n t s f o r

(0 :=

BOD)

the Evil

//

Cheek PCoN Regist€r

Genius

( RC2 = 1r RC3 = 0, BOD = 1,

// // //

BOD EaDDeneal Not a Gooal Pow€r llp Inallcat€ Prc Mcu Powereil UP Onc€

//

No Browa

//

IJoop Forever

2.

) Ou!

Detect

Reset

3. !rhi1e(1 )

//

== 1)r

Elral cBoD

cBOD did not simulatewell,which addedto my problems in trying to figure out what washappening. Now,whencBOD is run in hardware,the hardware powers up with the greenLED, and when the potentiometeris adjustedto a lower voltage,the greenLED dims a bit and then tums off completely.And, when the LM371'svoltageoutputis raised,the red LED tums on,indicatingthat the applicationcode(and hardware) hasrecognizeda brownoutvoltagesituation. In everyPIC MCU datasheet, Microchip marks eachbit whena registeris defined.Eachregisteris definedand then labeledasRegister#-x (where# is the datasheetsectionand x is the numberof the register definitionin the section),and the ability to read and/orwrite the bit alongwith its power up valueis specified.Readand write are specifiedwith a R andW, respectively, aswould be expected,but asI showin Table5-1,there are four initial valuesthat you should be awareoi Microchipdocumentationis uniformly excellent, and it is very unusualto find a mistakelike the one I found.(In caseyou are wondering,the mistakeis in Register3-1:PCON Registerof DS31003.{,pages314,and I havenotified Microchip of this error.So hopefullyit will not appearin later datasheets.) When you are confrontedwith a problem,asI havebeenin this experiment,wherethe codedoesn'twork as you shoulddo the [ollowing: expected. 1.

Check over the codeto seeif you can find the problern.Simulation(althoughnot possiblein

4. 5.

this experiment)of the program is alwaysa goodidea. Rereadthe datasheetto make surethat you are usingthe function properly.Often the datasheetwill haveexamplecodethat you can use. Look for apnoteson the Microchip web site that illustrate how the function works.Don't expectthere to be an apnoteon everyfeature built into the chip that you are using.You may haveto look at how the function works (and is programmedor wired) in anotherPIC MCU part number and understandany differences. Look for examplecircuitson the Internet using Googleor anolhersearchengine. Compareresourcesto find any discrepancies or cluesasto how the featureworks by cornparing the different descriptions.

rd f3

w

!_t

ia'

l"j&J t

It's importantto know that theseinstructionsare for gettinga hardwarefeatureof the PIC MCU working;they shouldnot be consideredthe most appropri ateway to debuga failing program.Later in the book I discusssomeof the techniquesfor finding a logic problem in a programand makingsurethat you havefixed it correctly.

i

f

i

(J

t$ |'{

Table 5-1 MicrochipEatasheetInilial FlegisterBit Value qno.ifi-rtinn<

r"*'

Eit PouJer Up Value MPaning 0

After Reset,the Bit valueis 0.

1

After Reset,the Bit valueis 1.

u

After Reset,the Bit is the samevalueasbefore Reset.

x

After Reset,the valueofthe bit is unknown.

5

Experiment 33-FUE Operation If you wereto look in the PIC16F684'S datasheet, you would discoverthat the functionof the analog-to-digital (ADC) functionis explainedover eightpages.I find this descriptionof the ADC function,althoughthorough,a lot more complexthan it needsto be.Using the ADC itself is surprisinglysimpleand doesnot require a lot of codeor understandingof how it works.In this experimentI am goingto explainthe functionand

S e c t i o nF i v e P I C l t F h B t l l l i c r o c o n t n o l l e n

Built-in

Functions

93

!

characteristics of the ADC and give you an example experimentthat samplesan incominganalogvoltage and displaysit on the eightLEDS of the PICkit I starterkit. The ADC functionof the PIC16F684canbe seenas a simpleblock diagramlike the one shownin Figure54;the linewith voltageto be measured is connected to a capacitorin the ADC. When the ADC operation starts,this capacitoris disconnected from the input and the voltagefrom the capacitolis passedto a comparator input.The other input to this comparatoris connectedto a slreepgenerator.whichproducesa ramping voltageat a known rate.To measurethe voltage(which canbe a maximumofVdd), the sweepgeneratoris startedand the time whenthe sweepgenerator'svoltvollageis ageto be grealerlhan thecapacitor's recordedusinga counter.This is reallyall thereis to it, althoughyou shouldknow a few other things,including beingfamiliar with the registersusedto control the ADC. The operationof the ADC is quite simpleand easyto integrateinto your applicatrons. Becausethe ADC operateswith the sweepgenerator, it doesnot executeover a singleinstructioncycle; it takesat least20 ps to perform the 10-bitdataconversionoperation.You shouldalsoallow at least12 ms betweensamplesto ensurethe capacitorchargehas changedto reflectany changein voltage.The time requiredfor the capacitorto chargeis why Microchip recommendsthat the impedanceof the signalshould be lessthan10k.These delaysmeanthatsamples shouldbe madeafter 32 ps or so,resultingin a maximum sampletiequencyof about30 kHz.This is fast enoughto implementaudiosampling,but not fast for manyreal-timedata-monitodngactivities. Fiveregistersare involvedin working with the ADC. The ANSEL registeris usedto selectwhich of the eightpossibleADC inputs (RA0 to RA7) will be connectedto analoginputs.On reset,the ANSEL register,which controlswhich of the eightbits are analog inputs,hasall its bits set.lf you look back at previous experimentsthat usethe PICkit 1 starterkit, one of the hardwareinitializationstatementsusedwasto clear

the contentsof the ANSEL register.For this experiment and any applicationthat requiresanaloginputs be measured,the bits representingthe analoginput pins are left set. The next registeris the ADCON0, which controls the operationof the ADC.This registeris usedto enableand start the ADC hardware,to selectwhich pin will haveits analoginput sampled,and to set the output fomrat.Thble5-2 liststhe functionof the different bits usedin the ADC. The sweepgeneratorhasan internal counter,which is run from a built-in RC oscillatoror the processor's clockand is known asthe A/D ConversionClock.It hasthe timing signalTAD. Its sourceand prescaler valueare selectedby bits 6:4of the ADCONl register. In Table5-3,I havelistedthe differentADC clock optionsand the resultingprescalervalues.TheTAD valueshouldbe between1.6ps and 6.4 ps for proper operationof the ADC, and this time is calculatedby simplymultiplyingthe PIC MCU's clock period by the TAD operationlistedin Table5-3.If you don't want to calculatethe TAD operationthat will give you the

Table 5-2 F U E 0 N 0B i t F u n c t i o n s Bit Name

Function

7

ADFM

Output Format:0 = Left Justified(ADRESH has8 Bits):1= RightJustified(ADRESH has2 Bils)

6

VCFG

VoltageRelerence biI: I = Vrel Pin (RAl); 0=Vdd

5

Unused

4:2 CHS

= RAo; AnalogChannclSclcct:000 0 0 1= R A l i . . . l l l = R A 7

1

GO/_DONE ADC OpeIalionStaft/EndIndicator

0

ADON

1= PowerADCr0 = ADC Off

Table 5-3 FDC0NI Bit Functlons Bit '/

TRD Operation

Unused

:'2 6:,1 0oo-Period r'3 001 Period * 32 010-Period xl-Internal,{UsRC 100 Pcriod* 4 * 16 I01 Period 110-Peiod* 64 Genefatof

Commentg

3:0

Figure 5-q

ADC bl.ockdiagram

94

l , a 3 P I C o l l C U E x o e ri m e n ts f o n t h e E v i l

Example:For a PIC16F6B4 runningat 4 MHzClock Period = 250 ns DesiredTAD = 1.6!s to 6.,1Fs ClockPe od +TAD Operation001 =250ns*E =2!s Unused

Genius

fastestADC operation,you cansimplyselectthe built(RC) clock-this runs at a nomiin resistor-capacitor nal 4 r.r.s and will allow the PIC MCU'SADC to operateunder all conditions. The fourth and fifth registersareADRESH and ADRESL, respectively. Thesetwo registersstorethe 10-bitresultof the ADC operation.The10 bits are displayedaseightand two,with eachregisterhaving either two or eightbits.I recommendthat you left justify the data,or storethe eightmostsignificantbits in ADRESH and the two leastsignificantbits in ADRESL.The two leastsignificantbits are generally consideredto be in the noiseregion,and their valueis not accurate;by readingonly the mostsignificanteight bits,you shouldbe gettinga reliableeight-bitanalogto digital conversion. With the registerssetup,you will setthe GO/_DONE bit (known asGO in PICC Lite compiler) and wait for it to go low.Hopefully,my description of how the ADC workshasn'tconfusedyou, becauseto carry out an analog-to-digitalconversionon a PIC16F684'sRAOpin, only the following six C statementsare required: INSEL

= 1r

ADCONo = / I BlE // Bit ll BiE / / BiE / / BiE A . D C O N I=

//

|

//

= ADSESE'

//

aa Analog

Turn on the sarDl.e

hput }Irc

the

hpu!

Value

This program salnpl€s the voltage on RAo uEing the A.Dc aaal DisDlayE the value on the 8 IJED3 uaiag .cr,EDDisD 2" as a base. rnfke 9realko 04.10.03

of

PORIA = 0t CUCONo = 7t ANSEI = Li ADCONo = // BiE // Bits // BiE / / B,.E // BfiLDCON1 =

I / ll.fi'l// Juat

on

' ;

ADC

oft Conpa?alorE ItAo ia art Aaalog

0b00000OO!i olr th€ ADC // Tlta 7 - I"ef,t ,tustifieal Salnlrle 5 - Uae vDD 4r2 - Chann€1 0 L - Do nol Start O - Tuln on A.DC 0b00010000r // Select lhe clock Foac/o == Ll

//

:--3

i*

Input

ti;"* a ;

( (ADcvalue & (1 << i)) PORTA = NOIPORTA til t

i

lat

rt

tshe I LEDS "on'r //DiEPlav Delay Loop == 0)

-*1' i i i

'.: i""4

Machine

case 0: starl Next' salllple // EiniBhefl, CiODONE= Lt LDCgtat€++t bleak; case L, / / waits for ADC to codnplete ( lGoDoNE) if PiniEheal ADCStsate++, // Sarple breakt in cas€ 2: // Save Sanple value "ADCvaIue " ADCVA].rIE = ADRESH' ADCSlate = 0t bleak; // hctirtr's l // elihw ) // End clrDc )

When you run this codeon the PICkit 1 starterkit, you will be ableto changethe valuedisplayedon the LEDs by changingthe potentiometer(marked"RP1" on the PICkit 1 starterkit). You may find that the least

Built-in

,

rurl-

t

5 e c t i o nF i v e P I C l , h F E g qf l i c r o c o n t r o l l e r

t

as

Loop Foreve!

PORTA = PORTAVaIUe lil t TRISA = TRISAVaLUe lil t // '.of l (A.Dcstatsel acrilcb ll ADC State

save sarll)le value After Operation

Po!

K€€p Track OI,eration

{

if

couldl also be ncODOl[E = 1rtr for A.Dc Eo wait Completse

Prcki!

//

nain( )

//

For this experiment,I haveusedthe scannedeightbit LED displaycodeto displaythe valueof the ADC. To ensurethat it doesnot negativelyaffectthe operation of the LED displaycode,I haveprogrammedthe ADC operationin cADC.c asa statemachine,withthe sampletaking placeover severalpassesof the LEDs. Thiswill avoidspendingtoo much time with any one LED lit longerthan the othe$. +inclutle CADC - DiaDlay /* the builts in rJEDs

= 0,

f o r ( i = 0 r i < g r i + + ) Each of I / t oor, thlough I (i = 0t i < Dlay, i++)t for

IntelnaL

. rr

= 0; lnt ADcvaluo int Dlay = 53r // LED Tirre on Delay Variable cotrst char PORTAvalue [8] = {0b010000, 0b100000. 0b010000,0b000100, 0b100000,0b000100. 0b00010o, oboooo1olt const cltar TRrgavalue [8] = {0b001111, 0b001111, 0b101011,0b101011, 0b011011,0b011011, 0b111001,0b111001)t c o n s t c l r a ! N O I P O R T At 8 l = t 0 , 0 , 0 , 0 ' 0 , 0 , 0 , O l l

(

Select th€ RC Clock

s-J L"{

& &

q!r' i, j; e.Dcslale

int int

while(1

(1 << 1)r

IGODONE)t

ADCValue

RAo iE

0b000000001r // 7 - I.eft ilustifietl 6 - uae vDD 4t2 - channeL 0 L - Do not Stalt 0 - Tulr on ADc 0b001110000r //

A.DCONo = AI'CON0 while(

Just

& WDTDIS & PWRTEN & IICIJRDIS CONI.IG ( II{TIO IJNPROTECT \ & ('T{PRO!!ECT & BORDTS & IESODIS FCMDIS ) '

Functions

95

r 1

significantbit flasheswith certainsettings:Thisis due to slightlydifferentreadingseachtime the ADC operates.If the leastsignificanttwo bits were alsoshown, you would probablyseesignificantlymore flashingat other potentiometersettings. What you shouldconclude from this experiment is that the most significant sevenbits of the ADC output will be accurateand the leastsignificanttbreebits shouldbe ignored. For this experiment,I am usingthe circuit built into the PICkit 1 starterkit shownin Figure5-5.This circuit consistsof a potentiometerwired asa voltagedivider with a currentlimiting resistorand a capacitor.The voltageoutput of this potentiometercircuit can be

I-Figure5-5

ADC circutt

readmore than one way,asI will showin the next two experiments.

rt; t i

ExFeriment 3t-.1-EomFarator Operation $i-a

Table 5-4 EMCON0BegisterBits and EomparatorOperation Bit

FunEtion C2OUT

Comparator2 Output. if (0 == c2rNV)

r!*

C2OUT= 1ifC2Vin1 > C2Vin, else// if (1 == C2INV)

tr*

1-t

I ,

1' J

f1

!i.ii ,!! 11

One of the measurements that I useto gaugethe difficulty of applicationsin this book is whetheror not the circuit I designand the codeI write works the first time.WhenI startedthis experiment,I had a perfect recordof 72 applicationsthat worked the first time I built them,and burned their codeinto a PIC16F684. Other factorsfurther bolsteredmy confidencefor first-timesuccess for this experiment:My plan wasto basethe codeon the previousexperimentand my familiarity with the PIC MCU's comparatorand integratedvariablevoltagereferencecircuits.In this experiment'swrite up,you'll get an explanationof the operationof the comparator,plus you'll get a story of hubrison my part.

C2OUT= 1ifC2vinl < C2VinC1OUT

if (0 == clrNv) CIOUT- I if ClVinl > ClVinelse// if (1 == CIINV) CIOUT= I ifClvinl - ClvinC2INV

Set to IDvertthe Comparator2 Output Condition(SeeC2OUT)

ClINV

Setto Invert the Compantor 1 Output Condition (SeeCIOUT)

CIS

ComparatorInput Switch,Usedwhen CM bits == 010

if (0==crs) RA1 is Clvin-

The comparatorcircuit built into the PIC MCU is quite simple.It consistsof two comparatorswith differing input and operatingoptions,which are controlled by the CMCONOregisterexplainedin Table5-4. Beyondthe CMCON0,a COMCON1 registeris used to controlthe operationof one of the built-in timers andsynchronizeone of the two comparators'output with a timer.I havepassedover this CMCON0 register becausetheseoptionsare requiredonly for specific applications The CM bits of CMCONO selectthe operating modeof the comparator(seeThble5-5).In most

96

Comparator1 Output.

RC1 is C2 Vinelse// if (1 == CIS) RAO is ClvinRCo is C2 VinWhen CM bits == 001

if (0==crs) RA1 is Clvinelse// if (1 == CIS) RAO is ClvinCM

l , a 3 P I C @l " l C UE x p e n i m e n t s f o r

ComparatorMode SelectBits (seeTable5-5)

the EviI

6enius

Table 5-5 EomparatorBperatingMode 5elected bg the EMEONOEM Bits

f'1

X

F0

EM 2:O Operation of Comparators

o

111(7)

ComparatorsOff Requiredsettingto useRAo, RA1, RC0,and RC1 asdigital I/O.

r-t

110 (6)

Comparators On, RCo is common Vinl for two compamtors.RA1 is Clvin-, RA2 is C1OUT,RCl is C2Vin-, and RC4 is C2OUT.

F.

101 (5)

Comparator 1 Ofl Comparator 2 On. RCOis C2Vin1 and RC1 is C2Vin-.

100(4)

Both comparatorsoperating.RAo is C1Vin1,RA1 is Clvin-, RCo is C2Vin1,and RCl is C2Vin-.

011 (3)

Both comparatorsoperatingwith commonVinl on RC0. RAl is Clvin-,and RC1 is C2Vin-.

010(2)

Both comparato$operatingwith commonVinl ftom Vref module. Clvin- and C2Vin- are selected by CMCON0 CIS (seeTable5-4).

001 (1)

Both comparatom operating with common Vinl on RCo. Clvin- selectedby CMCON0 CIS (seeTable5-4) and RC1 is C2Vin-.

000(0)

ComparatorsOflAnalog input on RA0, RA1, RCo, and RC1.Default setting.

ss

To Comparator Inputs

w *r I Figure 5-5

Vref circuit \ J

Table5-6 VFEONFlegisterBit Bescription

o u !{

Blt Name Functlon applicationspresentedin this book,I havetumed the comparator bits off by writing 0b0111to the CM bits. For this experiment,I want to use RAO as a comparator input along with the controllable Vref voltage sourceto measurethe voltage coming from the potentiometer built onto the Plckit 1 starter kit. The Vref sourceis available only to the comparator. In someother comparator-equipped PIC MCU part numbers,the Vref value can be output to other devices.This circuit consistsof a tapped voltage ladder with different voltagespassingthrough a 16-to-1 analog multiplexer. The VREN bit of VRCON controls the power,andVRR selectsthe operatingmode (see Figure 5-6). Figure 5-6 also lists the output voltages basedon the stateofVRR and the VR bits of VRCON which are listed in Thble 5-6. To demonstratethe ability of the comparatorand Vref circuitry asan analogto digital converter,I used cADCc asa basefor the eighth LED output control loop,and I usedthe statemachineto poll the ADC. I cameup with cComp.cin which I found the potentiometer's wiper voltageby usinga binary searchalgorithm. lliacluile - R€aal th€ ccoq) /* uBing conpalator/cr€f

PICkit

Pot

laDut

Vollage

Thia Drogrrm arrrpleE the voltag€ on RlAo uaiag lbe CorE)arator rdith the Cref Dtotlule anfl DiEplayB tsbe four bit r€Eults on th€ l€aEt Eigaificant LEiDa on Eh€ PICkit PCB.

5 rt

'7

VREN vref Module PowerEnable

6

N/U

Not Used

5

VRR

Vref Voltage Select (1 = Low Range; 0 = High Range)

gl Ft )r,

4 N r u

Not Used

3:0 VR

VoltageSelectionBits (seeFigure5-6 for formula) I 7

}{ lth€ ADC oDelation algoritbrn

consiatg

of

a binary

aearch

o U

Ilyk€ predlko 0{.10.05

l{ -CONjrIG(INTIO I'NPROTECT \ FCUDIS) t

F'

& WDITDIS & PWRTEN & T''CLRDIS & & I'IIPROTECT & BORDIS & IESODIS &

c+ F.

LnE lnt cdDstate

= 0r

//

Nextvrefvalue; vrefvalu€ t Di69value = 0t

//

K€€p Track ODeration

of

Comparator

DisDlay value to avoLtl F].ashirg int Dlry = 53r // LED !!ime on Delay variable coaat char PORTAVaIUe [8] = { 0 b 0 1 0 0 0 0 ' 0 b 1 0 0 0 0 0 ' 0b010000,0b00010o, 0b10000o,0b00o100, 0b000100, oboooolo],

S e c t i o Fn i v e P I C l , b F b A q i c n o c o n t r o l l e r B u i l t - i n

Functions

97

L) X

corr6t

char

colrst

char

nain(

= t0b00X111, 0b001111, 0b10x011,obx01011, 0b01x011,0b011011, 0b111001,0b111001), NOTPoRTAI8] = t0, 0. 0. 0, 0, O, O, O], TRISAVaIUe [8]

)

t PORTA = 0, C M C O N o= 0 b 0 0 0 1 1 0 1 0 r // Iaitialize Conparators // BiE 5 - Conp 1 Output (v- > v+ = X) // BiE 4 - Inverts corlr (RcO C2 rnpur ) // BiL 3 - RtAo C1 Inpur // Rit 2tO - CofirDarator with Cref VRCON = 0b10L00000r // Vr€f MoaluJ.e Control //Bit7-Enable // BiE 5 - Low Range (0 - 2/3vdd) // BiE 3.O - anaJ.og Lev€Ls aNSEI, = 0t // No ADC hputa while(l

{

== 1)

//

Loop

For€ver

f o r ( i = 0 r i < 8 r i + + ) | / / Loop through Each of the 8 r,EDS for (j = 0, j < Dlayr j++), "on" D€tay Loop //Display (0 == (DisDvalue & (1 << i))) if PORTA = NOTPoRTAlil, e16e PORTA = PORTAVaIU€ [i] , TRISA = TRISAVaIUe [i] , l // rof (Conpstate) svritch // CdtE)arator Stat€ l4achin€

{

// = 8t // Nextvrefvalue = 0; vrefvafue vRcoN = 0b10101000t Compsta!e++i

Filrished, Start Salnple sEatL witsh rligh

N6xt value

b!eaki

/ / waiE for ADC to conpl€te lO != (o'tcolro & (1 << 6))) // v!^ > vtef? (1 == clou!) if // vin > vref? = Vrefva1ue Vrefvalue + Nextvrefvatue, €tse // No - Take Alray fron Vref VRCON = VRCON - Nextvrefvalue, I I Ttr \e'*E bit of binary search = Nextvrefval"ue Nexlvrefval"ue >> 1; VRCON = VRCON + Nextvrefval.uet (0 -= Nextvrefvalue) if ( / / Einisheat, Display New vaLue = Vrefvaluet Dispvalue = 0i Conltstate // and Restart Analog lt€asurement /l fi , break; ) // hctiws ) // elihw // Erd cconp ) //

if

To measurethe potentiometervoltage,you could haveuseda simplealgorithmthat startedwith the Vref voltageat a minimum value(VR = 0b00000)and incrementedit until the comparatorchangedstate.I usedthe binary searchalgorithm,becauseit requires the logarithmbase2 comparisonsof the numberof bits insteadof potentiallyhavingto run througheach bit. In this case,usingthe binary searchalgorithm reducedthe number of comparisonsfrom a maximum

98

of 16 to four.A binarysearchalgodthmusedin comparisonoperationslike this one continuallyhalvesthe comparisonincrementuntil nothing is left.As I show in the followingpseudocode, a test valueis used,and if the valueis greater,it is left asis,else,the valueis removed.After the comparisonis complete,the test valueis dividedby two againand addedto the comparisonvalue.Thisis repeateduntil the comparison valueis zero. = Maxinu! / 2; // Stalt at 1/2 Maximum = Conparisonvalue; ConDarevalue // add to the Cofiurarison value u'hiL€ (0 != Coq)arisonvalue) // Repeat while a value to Add { I / Deternine if vaLue to b€ Saneal (Conparevalue if > InputvaLue) = Compalevalu€ - Conparisonvalu€i Cornpar€Value = cdll)arisonvalue comparisonvalu€ / 2t // R€peat O!|eration = Comparevalu€ Conparevalue + ConDarisonvalu€, | / / eli})w ComparisonvaLue

The binarysearchis ideal for digital systems becauseit works nativelywith binary bits.The previous codeis not significantlymore complexthan codethat doesan incrementingcompare,and the operational speedgainedis significantand growsin significancefor eachadditionalbit to compare. As I alludedin the introductionto this exDeriment. whenI firstrurnedon the originalcodenothinghappened.I wasvery surethat the hardwarewasgood (it worked fine for cADC.c),so the problem wasclearlya programmingproblem.This is a very difficult program to debugbecausethe MPLABo IDE simulatorwill not simulatethe operationof the comparatorandVref modulewith an analoginput.To find the problem I reviewedthe operationof all the program,sstatements (fortunatelyit's a shortprogram)and found the following one line if

( 1 = = ( C M C O N o& ( 1 < < 5 ) ) )

that neverbehavedasif the expressionwastrue.This instructionANDS the contentsof CMCON with bit 6 set and returnstrue if it is equalto 1.My initial responsewasto rereadthe comparatorsectionalong with previouslywritten applicationsto figure out if I wasdoing anythingwrong.The codelooked great.I then changedthe programso everyhardwareregister wasrenamedto a variable(for example,CMCONO became CMCONO)and went on to try different valuesof _CMCONOto find out if therewassomethinsI wasn'lseeing. Usinglhis merhodI discovered there wasn'ta valuefor _CMCON0 that would causethe expressionto be true. I looked at the expression"1 == (CMCONO& (1 << 6))" in the if statement,and when I checkedits

l , e 3 P f C @i l C U E x p e r i m e n t s f o n t h e E v i I

6enius

resultusingthe simulator,I discoveredthe error:the expressioncanneverequal1-it will equal 0b01000000, but never1.WhenI changedthe expression to testfor not zero the programworked fine (this is commentedout statementin ccomp.cabove).Further improving on the statement,I simply polled the C1OUT bit to be high,rather than manipulatingthe contentsof CMCONO. This descriptionofwhat I did to solvethe problem wasn'tput in to scareyou.You probablyaren't comfortableyet doingthis kind of debug,especiallyconsidering the simulatorcannotsimulatethe operationof the comparatorandVref hardwareand registers. But I want to point out the stepsI followed: 1.

2.

3.

Check over the hardwaredocumentationto make sure the hardwareinterfacesare properly coded. Test the operationof eachstatement.If necessary,changefrom a registerto a variable;a variable can be declaredby usinga registername with an underscore(_) characterprecedingit. Clearly articulatewhat the problem was.For me the problem wasthat the registerexpres-

4. 5. 6.

sion "(CMCON0 & (1 << 6))" could never be equal to the comparisonvalue (1). Fix the problem accordingto what you feel the problem is. Testthe fix usingthe simulatortools createdfor the task of discoveringthe problem. When you are satisfied,burn the new program into the PIC16F684and seeif this works better ror you.

You shouldbe able to follow thesestepsin debuggingyour own applications, and althoughthey may you will seemslow and tedious, find the problemand have an idea how to fix it. I want to point out that the root causeof my problem wasmy doggedinsistenceon programmingapplicationsusingstandardC and not usingPICC Lite compilerextensionswherethey make sense.As I have said,C is not well designedto manipulateindividual bits,but PICC Lite compilergivesyou the ability to accessbits individually,and all the registerbits are codedin the includefile.

rs: * *e4 fl1 r)

*\r ;-i ,.-*

9 . 1 r :ai

!

.1,::9 '_*11

i,i

Experiment35-l-UatchdogTimer

;:.,ir,:

.{:-: 1 Ptc15F584 1 10-LED bargraph I

display

0.01 pF capacito! tlpe)

i

Breadboard-mountable (E-Switch SPDT switch EG1903 reconmended)

lfi

Two-cell AA or AAA battelY pack

D}4M Needle-nose

AA o!

AAA batteries

pliels

B!eadboard Itiling

kit

T\e WatchdogTimer(WDT) is built into all PIC microcontrollersto provide a reliablemethodof resetting the rnicrocontrollerif executioneverstopsfollowing the expectedexecutionpath.This can happenwhen the PIC MCU runs in a high electrical-noise environment,suchasnear the flybacktransformerof a TV set or near a car'sienition svstem.When the WDT is

enabled,it continuallycountsdown a set delay,and if it is not resetwithin this period (usingthe clrwdt instruction), the WDT resetsthe PIC MCU and execution startsover.Personally, I haveneverusedthe WDT in any of my applicationq and I can think of only one commercialapplicationthat takesadvantageof it. Along with this,the advancedresetfunctionsof modern PIC MCUs eliminatemuch of the practicalneed for the WDT. Chancesare you will never require it in your applications, but you shouldbe awareof it and

S e c t i o nF i v e P I C I h F h g q f l i c r o c o n t r o I l e r B u i I t - i n

Funct i ons

;.tr.

(any

99

H

0, ,J

r en rt "r{

tr,

rv tFa ! t

4""{

&.} 1,".

how it operatesas there is one trap you will probably fall into whenyou work on your own applications. That trap is to not correctly disable the WDT in the configuration fuse specification.Many new PIC MCU application developerswill specify only the labels for the configuration fuse functions that they believe are required for their applications.Unfortunately, the configuration fuse functions are both positively (bit set) and negatively (bit reset) active,and not specifyinga value for the bits could result in an unwanted function being active.The most common unwanted function being made active is the WatchdogTimer. When the WatchdogTimer is enabledinadvertently in a simple application,with no clrwdt repeatedly executing in the application,the PIC MCU will reset itself after two secondsor so.The reasonfor the reset is indicated asthe _TO bit of the STATUS register being reset on power up.The problem ig that the application will have executedfor a couple of seconds,giving the appearancethat the application started correctly,but a software problem causedit to resetitself and start over. The reasonfor the reset can be clearly seenby running the MPLAB IDE simulator, by setting a breakpoint at the first executingstatementand addingthe Stopwatchfunction.If the WDT is active,the program will executethe first statementa secondtime,about 2.1secondsafter the start of the simulation.Ifyou see this behavior at any time during your application development,you can fairly confidently assumethat the WDT is becoming active. The circuit that I usedto test the operationof the WDT resetis shownin Figure5-7 and wired on a breadboardasshownin Figure5-8.Thetestcodeis cWDT.c and increments the number of LEDs that are lit on the 10-LED bargraphdisplayonceevery500ms To disablethis function, simply changethe WDTEN argument to WTDIS in the _CONFIG macro.Unless you are goingto usethe WDT in your application, then the WDTDIS argumentmustbe presentin every applicationthat you create. You should find that after you turn on power to the application,the first four LEDs light but are then turned off whenthe tenth LED is lit, and the process repeatsitself over and over again.The 2.1-second delaybetweenWDT resetsis determinedby hardware within the PIC MCU. I will discussit in more detail later in this chaDter.

1 OL E D Bargraph

-:---E,, t I I Side

Figure 5-7

WDT circuit

Figure 5-8 Testapplication to demonstratethe operattonof theWDT reset

Previously I stated that I know of only one application that takesadvantageof the WDT. That is the Parallax BASIC Stamp(and BASIC Stamp2). In these PIC Mcu-based devices, the WDT is usedto time the s/eepstatement,which puts the BASIC Stamp to sleep for increments of 2.3 seconds(the rnaximum WDT resetintervalfor the PIC MCU chipsthat are usedas the basisof the BS2).

, r.{ FI

r't I 14{ a,

r-1

100

l , e i P I C @f l C l JE x p e n i m e n t s f o r

the Evil

6enius

Exp e r im ent 36- S hor t T i me rD e l a g sU s i n gT MF 0 WhenTMRO overflows,it setsthe T0IF bit of the INTCON (interrupt control) register;to do so is an interrupt request.I do not discusshow interruptsare implementedin this book,but this bit canbe usefulto poll to find out if TMR0 hasoverflowed.Inthe lowend PIC MCUs,no interrupt capabilityexistsand no T0IF bit existsso the contentsof TMR0 will haveto be continuallypolled.

For mostof the experimentspresentedin this book,I usesomekind of incrementingor decrementingloop for producingdelays.In the latter half of the book,I showhow you cancreatevery precisedelaysby counting out the executiontime of the instructionsand loops of instructions. But whena delayis requiredfor programmingin C, I tend to createa simpleloop and then tune the delayvaluesempiricallyusingthe MPLAB IDE simulator'sStopwatchfunction.The empirical approachworkswell for mostlarge(i.e.,tensof ms or longer)delays,but for shorterdelaysthat requiresome precision,this methodjust isn't goodenough. A better way of producingaccuratedelaysis to use a timer.ThePIC16F684hasthreebuilrin timen that you can usefor producingdelaysof known lengthsas well asfor someof the hardwareperipheralfunctions built into the microcontroller.In this experiment,I will introduceyou to the operationof TMR0 (or Timer 0) and how it canbe usedto produceaccuratedelaysup to 256ps.In the following experimentEI will present the other two timers,their standardoperation,and how they work with peripheraldevrces. TMR0 is an eighfbit timer that canbe driven either from an externalsourceor from and internalinstruction clock.Most applicationsusethe instructionclock asa methodof providinga set delay.In TMR0's basic configurationwhile runningin a 4 MHz PIC MCU, delaysof up to 256ps (23)canbe addedto the application.An externalsourcecanalsobe used.And. as somepeoplehavenoticedin the datasheets for different parts,the PIC MCU TMR0 modulecantake up to 50 MHz of input,leadingto someinterestingpossibilitiesfor measuringvery high-speedsignals. Control for the input sourceforTMR0 is the T0CS bit of the OPTION register(seeFigure5-9).The OPTION registerprovidesa numberof executioncontrol bits for the I/O pin internalpull ups,Watchdog Timer/TMROoperation,and interrupt operation (Table5-7).When you are working with the different hardwarecapabilitiesof the PIC MCU, you will find the OPTION resisterto be a verv usefulresource.

TheT0IF overflowbit is set whenTMRO changes from OxFFto 0x00and is the basisfor basicdelaytiming.Assumingthat the internalinstructionclockis usedfor TMR0 and this clockis 1 MHz (the instruction clock speedof a 4 MHz PIC MCU), the formula for determiningthe delayis: Delay

(in ps)

= (256

TMRo Initiaf

Value)

So,to specifya 200ps delay,the formula canbe rearrangedto find the TMRo initial Value: TMRo Initial

Value

= 256 DeLay = 256 - 200

In cTMRO.c,the operationis demonstratedfirst by the while loop in which the incrementingof TMR0 can througheach be seen.Thisis done by single-stepping

TOCKI Fosc Figure 5-g

BasicTMRq

Table5-7 OPTI0NFlesisterBits Bit Name Number Function _RAPU INTEDG

'/

Enable PORTA pull ups

6

Selecttheedgefor RA2 inlerrupt request(1 = Rising) Selectthe TMRo clock source(1 = RA2, 0 = lntemal Clock) Selectthe
PS2:PSo 2:0

S e c t i o nF i v e P I C I t F t A q f l i c r o c o n t r o l l e r

wDT.0

\ alue(Prescdler \ alueSeleclprescaler ?Psr:Ps\

BuiIt-in

Functions

1.01

statement.Each C statement is made up of multiple PIC MCU assemblylanguagehstuctions, so the different valuesby which TMRO incrementsshould not be a surprise. *inclutl€ - 1'!tR0 Opelat.ion cTu8o.c /+ Thia TllRo I t

*-{ :jc{

i

:

i

Drogram dlenonstrates Harakra!€.

ant[ Short

the

Delays

oD€ration

of

th6

rE ke Drealko 0{.11.24

-CONUG(INTIO UI{PROTEC! \ FCMDIS ) t

& WmDIS & PV|RTEII & I'ICLRITIS & I'NPROTECT & BORDIS & IESODIS

1 a-

{ OPTION = 0 b 1 1 0 1 1 1 1 1 t Bun TMRo from

nhi16 t

=t\-i

-:,-,

// Denon6tra!€ (1 < 1000) = i + 1t a fairly

TgRo - 55t l / I'riEi,alize ToIF = 0t / I \$n oft

the

Cloch

Opelatl.on

pr€clae

of

200 us

TlR0/Blealrl)oin! Peniling

OEciLlator

rnt€rrupt

TMRo

tl€Iay

]

// rchtle / I NoP O t //

Enabl€ T!4R0 Oeerflorc to Request ( !ToIF), Wai.E for 1l!4R0 !o O'lrerflow

whil€

(1 == 1)t

//

Breakpoint

Here //

- ,Iim€

to

Ints

Previous

I.ooD Foreve!

Enal cT!,1R0

In the secondpart of cTMR0.c,I demonstratehow to code a 200 ps delay controlled by TMRO.The first statementis putting in the TMRO Initial Value,whichis followedby a statementresettingthe TOIFbit, and then one setting the T0IE bit to enable the interrupt request.In the while loop, I am simply waiting for T0IF to becomeset when TMRO overflows By clickingon "Debugger"and "Stopwatch,"and then placing breakpoints where I have indicated in cTMR0.q I was able to time the execution from the settingof the TMR0 Initial Valueto the final NOPO;.I found the delay to be 207instruction cycles,which is an effor of seveninstruction cycles.This translatesto a delayof 3.5percent.For mostpracticalapplications, this error is acceptable. Although someapplications require absolutelyprecisetiming, when providing a basic delay,an error of a few percent will not negatively affect the operation of the application and will keepyou from carryingout what is essentiallyuseless debugging.

Here Requ€stE

*i

Experiment 37-Using the TMH0Prescaler

,l

i'4.{

When you looked at the OPTION register definition (seeTable5-7),you probablynoticedthe PSA bit, which selectedwhether the prescalerwaspassedto TMRO or the WatchdogTimer (seeFigure 5-10).The prescaleris a programmablecounterthat canbe used to changethe TMRO (or WatchdogTimer) timeout

102

interval. This convertsthesedelay interuals from just a few hundredms to severalps or evenseconds The prescalercanbe usedwith eitherTMRO or the WatchdogTimer, and its use is selectedby the PSA bit of the OPTION register.When the prescaleris selectedfor the timer,it dividesthe incomingclock signal accordingto the OPTION register's PS bits, with the divider being the zPs2'Ps. When the prescaleris usedwith TMR0, the signal is slnched with the internal instruction clock, which results in another division by two. So essentially, the prescalerdividesthe TMR0 * 1. input by 2Ps2'Pso In cTMROPre.c,I specify that TMRO is driving by the internal instruction clock, and I also reset the T0CS bit, which passesthe clock signal through the prescaler.

l,ei PfCo ilCUExpeniments for

the Evil

6enius

( ltrolP), whil€ NOP(),

//

BreaLDoint PteviouB

TURo = oxFFt

l/

Exec\rEe 255 ci'cle Delay/Breakpoint flele

- Tine

II€re

to

i.1: {}

ToIF = 0t

Figure 5-10

f , o ! ( i = 0 r i < 10r i++), ll I'rtRo = TI.,IRo I 0 x 8 0 r // ( ! ToIF) t lrhile NOP O T // BreakDoint Previous

CompleteTMR}

(1 == L>i

lthi1e

Becausethe prescalerbit selection(from PS2to PS0) is still set,the prescalerdelayis 1:256.Or, put another way,TMR0 is updatedonceevery256instruction cycles. *iacludle - TuRo operatioda ctMRoPle.c /* P!€acal,er This Drogram alenonsllet€s r!!Ro anal P!€sca1€r.

lbe

with

th€

oDelation

of

the

rryke Drealko 04.LL.2A

)

//

nain(

)

{ OPIION = 0b11010111t // Rua T!{Ro with //

1:255

Use Same Coat€ as fairly of uct![Ro.c"

TURo = 55r ToIE

= 0i

ToIE

= 1t

m{Ro = 0x6t

$IRo

preciae

200 us

al€lay

//

Run TuRo with 1!{ PreacaLer Execute 1000? cycle D€Ia1'/Bleal
t //

Brealeoint Ptevioua

0b11010111r

= o:iFF;

t'o

//

//

t1 ;"'i,

.$

s

Loop Eorever

t:,

Like cTMRO.c,cTMR0Pre.crequires the MPLAB IDE Stopwatchto understandwhat is goingon. In the first TMR0 delay,TMR0is loadedwith an initial value of 56,and the time taken to reachthe NOP0; is 51,208 rycles.This is 256times200plus 8.The productof 256 and 200is exactly what was specifiedby the TMR0 Initial Value,and the eight additional cyclesare similar to the seven-cycle overflowof the previousexperiment. prescaler, Usingthe a delaycanbe specifiedas: = 2r"""ur""

I X

i: (256 - TMRo Initial

Value)

i:.L

wherethe prescalervalueis definedasthe base2 logarithm of the delaydividedby 256(the maximum TMROvalue).This is a complexway of sayingwhich power of 2 would produce a number large enough to storethe valueof delay.For example,if you wanteda 1 msecdelay,you would usethe followingprocess:

].tr' 'r i:l

Pleacaler

Initialize I'llRo/BreaLpolnt He!€ // 'I'luin off Penaling Intelrupt Requ€atE TURo Ov€rflow to // E[able Requ€st Ints ll WaLE fot I'MRo to Overf,low Here - Time Eo .// Breekpoinl Previous

OPTION = 0b11010001r

OPTIoN -

- Time

Hele

Prescaler = Log, fnt(1,000/256 = Log, 3

) f::iJ

//

(!T0Ir)r rrhile NOPOr

loIF = 0, roIE = 1, ( ! T0Ir) while NOPOT

//

waj.t a Eew cycles set Bit 7 Again

Enal cI'MROPre

Delav ( INTIO & WDTDIS & PWRTEN & !4CIJRDIS & -CONFIG I'NPRC'IECT \ & I'NPROTECT & BORDIS & IESODIS & FCr{DrS ) ,

ffi

ll6re

- TLne to

Run ,ITtRo with pteacale!

Execute 256 Cyc16 D€lay/BreakpoinE Eere

TOIF TOIE

S e c t i o nF i v e P I C l h F b A q

1:255

t**: Now to find the TMR0 Initial Value,the formula is rearrangedagainto the following: TMRo Initial 2P'4€Ler

Value

= 256 -

(Delay

t1''f

/

+ 1)

,: :i

= 2 5 6 - 1 1 A 0 0/ 2 t ' r ) = 2 5 6 - 1 7 A 0 0/ 2 ' ) = 2s6 - t1400/ 4)

{r} f-1

The seconddelayin cTMR0Pre.cshowsthe delay producedby this calculationand executedin 1,009 cyclesaccordingto the MPLAB IDE simulator. The final two timer delaysdemonstratewhat happensif you incorrectlypollTMR0 duringits operation. In both cases, I setTMR0 to OxFF,and with a 1:256

icnocontroller

BuiIt-in

Functions

103

i*i ,€:

;*'9

ra

prescaler,you would expectthat the delaywould be 256plus 7 or 8 extra cycles. And, this waswhat I got (264cyclesspecifically).In the secondcase,a few cycles in,I write to TMR0 again:This couldbe considereda no operation becauseI am writing TMR0 with the samevalueasthe one alreadystoredin it. When you time the secondcase,you will discoverthat the delayis significantly different than the first. In my case,it was 429cyclesinsteadof the 264of the first case.

The difference is that I am writing to TMRO. Even though I am not changingthe value of TMR0 (and this canbe confirmedin the simulator),the write operation alwaysresetsthe prescaler. This is true for wdtes to any timer that hasa prescaler(e.g.,TMR1).For highJevel programming,this is not an issue,but it will be when you are programmingin assemblerand you just want to testthe valuein the timer.Make it a rule to always savea timer valuethat hasbeenread somewhereelse.

tfi

Experiment 38-Long TimerDelagsUsingTMHI

nal rrt 9""S fi!

Table5-8 TICONFlegister Eit Name

Number Function

TlGINV

&{

TMR1GE

{tt .r* '.L

t

Lir &.; iJ x i

]

I

! -

Onceyou haveworked with TMR0, you will not have any problemsusingTMR1 ro provide the samedelay functions.Looking at a block diagramof TMR1 (see Figure5-11),you shouldseea lot of similadtiesto TMR0. The major differencesare thatTMRl's operation is controlledby a dedicatedregister(TMR0 has somefunctionsspecifiedin the OPTION register), TMR1 canhavea uniqueoscillatorassignedto it, and, mostimportant,TMR1 is 16bits in size.ThesedifferencesmakeTMR1 quite a bit more flexiblethan TMRO and one that you shouldconsiderusingin all your applications. TheT1CON register(seeTable5-8)is usedto control the differentexecutionaspectsof TMR1, including its sourceand prescalervalue.In rnanyapplications, a 32.768KHzwatchcrystalis connectedto TMR1, giving the PIC MCU a real-timeclockcapability.The overflow output of the clock can be usedas an interrupt requestsource,similarto TMRO.Or it canbe usedin

,?r

Timerl Gate Invert (1 = ExternalTMR1 control bit is activelow) 6

ExternalTMR1 Control Bit Enable (1 = TMR1 controlledby extenal control it whenTMR1ON is set)

T1CKPS1:0 5:4

TMR1 PrescalerSelect(0b11for 1:8. 0b10for 1:4.0b01 for 1:2,0b00 for 1:1)

T1OSCEN 3

EnableExtemal Oscillatorwhen set

_TISYNCH 2

Resetto SynchronizeExternal Clock to InstructionClock

TMR1CS

1

TMR1 Clock SourceSelect(1 = Extemal clock,0 = Internal instructionclock)

TMR1ON

O

Set to EMble TMRl

two functions of the Enhancetl CapnrdCompard PI{M (ECCP) module,which will be demonstratedin more detail in the next experiment. I createdcTMRl.c to demonstratethe code requiredto createa 300ms delay: *incluale /* c1'!tR1. c - T!|R1 Denonstslalion This TllRl

Droglam tlemonBlrat€s Haralware.

the

op€raEion

of

the

myke prealko 0{ . 11.29

*i t..

!&

CoNFrG(INTIO & WDIIDIS P!9R,TEN & MCIJRDIS I'NPROTECT \ & UIIPROTECT & BORDIS & IESODIS FCr'rDrs ) ,

Figure 5ll

BasicTMRI

104

l , A 3 P f C @i l C U E x p e r i m e n t s f o r

i.;

the EviI

6enius

&

//

Itse Tl41 for

a 300 ns alelay

Parameter

cTMEl.c

PIC MCU Instructions

22

File RegisterBytes

0

2

ProgrammingIterations

1

tt

l)

1.,, 3

T1CON = 0b0011000L, //

TvaL O|r/lnternal 8x Preacale! TMR1E = ( 5 5 5 3 5 - ( 3 0 0 0 0 0 / 8 \ l > > a i a 300 ma alelay // InltialLze (55535 - (300000 / 8)) & oxFEt = ITMR1IJ a, ll Enable PeriDhelal In!€rrul)ts = 0t

TIIRIIF

lllJ,i Peatliag InlerruDt off RequeatE TUR1IE = 1r to // Eaab1e |!URl. O!'erflow Requesl rnts (lTuRlIF)r while // waits fo! tn{R1 to Ovelflow Here - Tfurc lo Previous NOP()' // Br€alr9oirt //

(1 == tr,

lrhile ]

Enil

//

ll

Loop

For€ver

cT!41

Looking at cTMRl.c, I was impressedwith its simplicity and wonderedhow it comparedto the standard for loop delaythat I usein mostof this book.The test caseI ffeated is the following cTMRlAna.c: *incluale cTMRlAna. c - coale Baseal 300 ms Denoastlatl,on /* proqlen lhis solution to

al€nonstrat€s cllMRl. c.

th€

equlvalent

coale

qyke plealko 04.rL.29

CONFIG(INTIO & }IDTDIS & PI{RTEN & !{CLR.DIS & UNPROIrECT \ & T'NPROIECT & BORDIS & IESODIS & FCUDTS), ungigrr€at

int

It

rnain ( )

(

//

rql X

Table 5-9 ComparingTMFIIto for Lcop DelagE

nain( ) t

uee coae for

NOPOr

//

a 300 ns alelay

BreakDoint

for (i = 0t i < 27272, 1++t, NOPO, Eer€ // Brealgroinl whil€ |

//

ba

(1 =-

1)r

//

cTMElBna.c

- T:i:r0€ to

b

o

P!€vLoua

Loop Forevor

o

F

rf

cTMRltAna

Table 5-9 comparesthe two programs over a number of parameters.The Programming Iterations parameter is the number of times I changedthe final value of the constant in both programsto get a delay that was within 300,000cycles.This measurernentconsistsof how many times I had to changethe code,rebuild it, andretestit with the simulator'sStopwatchto get the specific delay.I wasn't surprised that usingTMR1 for longer delayswasbetter than the for loop; I was surprised at hovt much better TMR1 was Aside from producing code that is two-thirds the size of the for loop, the TMR1 delay was also much faster and easierto get working correctly. The obvious question that arisesfrom this analysis is why people use the for loop to create delays.I believe two answersexist to this question.First, most low-endPIC MCUs (andlow-endmicrocontrollersin general)do not havea 16-bitcounteravailablefor delays,so they have gotten into the habit of creating a delayusingthe for loop.Second,simplynobodyhas thought to do this analysisbefore.But if they had, the better delay would be obvious,and maybe somebody would have written a macro to produce the delay.

H€re

(r) 6

I

r

o 4

q €

l,r,

u o X

U

o

ts 0, \< CI

a

F.

5

q

Fl

K

n H S e c t i o nF i v e P I C l , b F h A qH i c r o c o n t n o l l e n

Built-in

Functions

105

;*

Experiment 39-ComparingClockOscillators

;.* *

.pl ,$ PIC16F58 4 Prc12F5?5 t

:

"r!

2 MIIZ oscillator

t-:

4 MHz clystal

d3

4 MHz celamic vrith internal

*E ij

DMM

I

NeedIe-nose pliers

1 470O resistor

Breadboa!d

1 l0k breadboard-mountable potentiomete!

Wiring

e

kit

33 pF capacitors

t-

i* ,:-*

{'i {*,

tlx i:-: {.-f {'f

t

,sl .:* ;*

di #

".4 :,.t $ {,1< i..a ,'.: 1:l:

4. ?k tesistor

0.01 p,F capacitors

a--.: ."

resollato! capacitols

Part of the evolutionof the PIC microcontrollerhas beenfor Microchipto provide accuratebuilt-in oscillators,freeingthe applicationdeveloperfrom the chore of selectingand wiring a clockcircuit into his or her applications. For peopleleaminghow to developapplicationsfor the PIC, this wasanotherpotentialproblem area:If the clock circuitrywasnot correctlywired,then the applicationwouldn't work.This is not a concernfor you.The oscillatorsbuilt into the PIC16F684and PIC12F675are surprisinglyaccurate,allowingyou to usethem insteadof externaloscillators.In this exoeriment.Iwantlo look at the accuracy oI thedifferent oscillatorsavailableto the PIC MCU. The mostefficientmethodof testingdifferentclocking circuitsis to usea frequencycounteror an oscilloscopewith a measurementoption.I realizethat most peopledo not havethis equipmentavailableto them, so in this expeiment I will usea very simplecircuit that will giveyou a goodvisualindicationof the accuracy of the different clocking methods.I will run two PIC MCUs (a PIC12F675and PIC16F684)at the sarne time,usingthe sameprogram,and then passa counted-downoutput to the differentpins of an LED (seeFigure5-12).For simplicity,I put both PIC MCUs on the samebreadboardasshownin Figure5-13,using a long breadboardto allow for lots of spacefor the different clockoptions. If the two freQuencies are identical,the LED will light and the brightnesswill not change.If the frequenciesare different. the LED will flash on and off. The

L06

I

22 pF capacitot

I

SPST breadboald-mountable switch

1 Three-cell crip

AA battely

3 AA batteries

slowerthe flashing,the closerthe two frequenciesare. If you are familiarwith tuninga musicalinstrument, you will understandexactly how this works. In this circuit. I will tse a cannedoscillator to drive the PIC12F675; this deviceis a highly accurateclock (usuallyto within 10Hz for a 4 MHz device)that is usedasa referenceclock.The PIC16F684clock will be changedto one of the four differenttypesavailableto it.Along with the internalclock,or cannedoscillator like the PIC12F675uses,the PIC16F684can be clockedusingone of the threecircuitsshowin Figure 5-L4.Thesecircuitsare connectedto the oscillatorpins of the PIC16F684. For this experiment,I am assuming that eachclock is runningat 4 MHz (the mostcommon clockspeedfor PIC MCU applications). The codeI usedfor the PIC12F675wascalled c675Clk.cand usesTMR1 to count down 5 ms before togglingthe output of GPIO0.ThePIC16F684uses appropriateregisternamesand similarcode,exceptit dividesthe constantby 4 rather than the 8 of C675Clk.c. To testthe differentoscillators,the only changes madeto the PIC16F684codewere in the confisuration

l , P 3 P I C @l l C U E x p e r i m e n t s f o r

the Evil

6enius

14

Prc16F684

x

PtclzF675

0.01 uE

tld 0.01 uF

o

Fl F.

3 o

5 ct (, -

I:

to

tI '

2 MHzOsc Enable

OscillatofPins

Figufe 5-la

Clock circuit

I

n

o 3 id s, n

Fr.

p

fuse clock specification.Theclock polling loop does not produce an exact 100IIz output;it actually outputs 99.78IIz due to overhead of the loop and the polling of the TMR1 registers I could have tuned this to an exact frequency,but by keeping the code constant between the two PIC MCUs,I didn't feel this was necessary.The differencesin clock speedswould show up asflashing LEDs. In Table 5-10,I have listed the different PIC16F684oscillatorsused,their output ftequenciesmeasuredby my oscilloscope(nominally 100Hz), their LED flashing rate, and the configuration fuse specification usedfor each. To try and improve upon the accuracyof the resrsnr/capacinr (RC) oscillator,I replaced the 4.7k resistor with a 10k potentiometer and tried to tune the signal.This proved to be quite difficult, and I never was able to closely match the PIC16F684'soutput frequencyto that of the PIC12F675. Next, I drove the PIC16F684using the cannedoscillator to look at the accuracyof the PIC12F675'sinternal oscillator.The PIC16F684'sinternal oscillator automatically usesa programmed calibration value,

q

o

ts

o o ?f

o (n

Figure 5-13 Long breadboard usedto test different PIC MCU 4 MHz clocking options

o

but the PIC12F675'sinternal oscillator can optionally run with calibration. I wascurious to find out how accuratethis clock was.Theresults are in Table 5-11. To enable the PIC12F675'scalibration. the followins

ts 0, ct

Fr. F

o rt

a S e c t i o nF i v e P I C I h F h B q H i c n o c o n t r o l l e r

Built

in

Functions 102

Crystal

Resistor/Capacitor

(Rc)

H

T"

a'!

F{

r-f .rl

PrcMcu ?un clkln -----

PIC Muu l"ru MCU

Pin

Pin

v, O

I:

T"O' Htn

t !

Figure s-lq

Clock options

codestatements(takenfrom the PIC12F675 datasheet)were addedto the start of the application: //

#aam baf

f,n

(l H

.-{

1{

a) *J'.1

X td

loaat

cLock

3, 5

RPO caLL 03FFh Getscalibrat€vaLu€ 010h

(Jt

+

PICMCU ClkOut Pin

r-l

iI

^--ilr\,----l--l

Optional 100- 200Ohm

PICMCU Clkln------------l

tl

LI rr{

lT

CeramicResonator

,r4

Li "FN

Clkout

I

U

s

PICMCU Clkln Pin

i

Ca1iblation i

b.f

t

call

gTATus,

morrlrf OSCCAL ^ 0x90 bcf STAIUS, r

RPO *enalaam

To get the PIC MCU's actual operating frequency, the scalingfactor 40,080is multiplied by the 100Hz output. This is the ratio between 4 MHz and the 10,022 cyclesthat were measuredin the MPLAB IDE simulaTable 5-10 EomFaringOifferentPlClSFEBr.l Clocking0ptions to a Fleference

tor for one complete output cycle.Using this factor, the PIC16F684's internaloscillatorruns at 3,987976H2 (0.3%error);the resonatorruns at 3,995,992H2(0.1% error); the crystal runs at 4 MlIz; and the RC oscillator runs at 3,330,662 Hz (16.77oenor).The PIC12F675's uncalibratedclockis 4,2U/49 Hz (5.6% effor), and its calibrated clock runs at 4,092,784Hz (2.3Y" enor). The obvious conclusionfrom this experiment is that the PIC16F684's internalclockand the PIC12F675's clock are quite good and are sufficiently accuratefor virtually all applications.The applicationswhere these clocksare not adequatewould be timing measurement (e.g.,in frequencycountersand real-timeclocks).In thesecases,either a cannedoscillator or an extemal crystalwould haveto be used.In older partswithout a

Table 5.11 PlE|aF675InternalOscillatorFccuracg

Clock Tcpe

Measured LEU Frequencg Flash Eate

_CONHG clock Parametef

Ealibration

Measured Frequencg

None

105.4Hz

severavsecond

Intemal

99.5H2

3 flashes/second

INTIO

Using CalibrationCode

102.7Hz

several/second

Resonator 99;7 IIz

2 flashes/second

XT

Crystal

993H2

1 flash/6seconds

XT

RC

83.1I{z

many/second

RC

l.08

l , P 3 P I C @l ' l C UE x p e n i m e n t s f o r

the Evil

LED Flash EaIe

Genius

builtin oscillator,the RC oscillatorcanbe used.But remember,you can't expectthe accuracyof the oscillator to be in the samerangeasthat of the crystalsand ceramicresonators. I shouldpoint out that the resultsof this experiment,althoughreasonable, are not completelyaccurate due to the limited samplesze of parts.Still the purposeof the experimentwasto showthe different oscillatorsavailableto the PIC MCU. how thev are

wired to the chip,and how they compared.When you repeatthis experiment,you may find that different partsbehavedifferently,and althoughthe overall resultswill be similar.the measuredvalueswill most certainlybe differentfrom mine.For this experiment to be completelyvalid,a largesamplesizeof the different partswould be required,and thesepartsshouldbe chosenover a wide rangeof manufacturingdates.

tl.;i !.' J 1t

::ar

ExFerimentt-.|0-Timedl/O Pin Flesistance

,,,-,'i'

Measurements Usinethe CCP

I

Pr c 1 6 F 5 8 4

1 10 LED balgraph

display

1 10of,) res i"stor t

10k breadboard-mountable potentiometer 470f,) 10-pin

1.,'.

resistor

'f:',1

2 0.01 pF capacitors

T,oo1 Box

1 SPST b!eadboard-mountNeedle-nose pl iers

able

Breadboard

fhree-cel,I clip

Breadboald

wiling

kit

switch AA battery

AA batteries

i1' i'-:j: L:i

Even if you are a teenager,I'm sureyou'veseenthe earlyvideo games(like "Pong"),in which the userwas givenan analogcontrol.The first home and personal computersalsohad analogcontrols,the joystick being the mostcommon.But did you alsoknow that 20 years ago,analog-to-digitalconverters(like the onesbuilt into the PIC MCUs) often costrrore than basicmicroprocessors? The ability to readpositioninformation wasvery importantin theseearlygamesand simple computers,but addingan ADC chip wasout of the questionbecausethe cost. Imagineyourselfasa designerof one of thesesystems.How would you providethe ability to read a potentiometer(whichwasnormallyusedto read the positioninformation)?You could usea comparator and a programmablevoltagereferenceasI haveused, but thereis a mucheasierway to do this-by measuring the time it takesa chargeto passfrom a capacitor throughthe potentiometer.If you havereadmy previous123RoboticsExpeimentsfor the Eytl Genius,you

would know that the ParallaxBASIC StampII hasthe ability to time how long it takesfor a chargeto pass througha resistor(seeFigure5-15).In Figure5-16,I showwhat the electricalsignallooks like.First the capacitoris chargedby an I/O pin, and then the I/O pin changesto an input to allow the capacitor'schargeto passthroughthe resistor,with the delayfrom being fully chargedto reachingthe I/O pins high-to-low thresholdbeingapproximatelyproportionalto the potentiometer'sresistance. As a rule of thumb, the maximum time delay for the circuit in Figure5-15is:

l:1;,

ii: r:,. i

f, !':l

TimeDelay=2.2XRe.tXC

So,for a 10k potentiometerand a 0.01pF capacitor, you would expectthereto be a maximumtime delayof approximately 220 ps. I say"approximately" because potentiometersand smalicapacitorsare not known for

S e c t i o nF i v e P I C l h F h 6 t { I ' il c n o c o n t n o l l e n

BuiIt-in

Functions

1.09

tlr rl": ,,,".,

The obvious way of timing the code would be to start a timer and save its value when RCPin changed state as in the following code:

vcc

I" Fiqure 5-15

rctimefunction

RCPinTRIS = 0i // Make RCPin an Output RcPin = 1., // c})arge capacitor ( i = 0 r i < o n e r n sr i + + ) , for / / waiL fot Charging RCPinTRIS = 1r // llake RCPin anal Intrrut TMRo = 0r // Rese! the Tirne! (0 l= RCPin) t while / / warL for Pin to Go Low = lltlll.Oi Potvalue // Save the Pot Value 'i" proportionaL // contains a value to the ResiBtance

But a betterway is to usethe Capturemodeof the ECCPTimer Generator.This function will savethe contentsof TMRl at an externalevent.Usingthe ECCP module,there'sno needto savevaluesor worry abouthow many instructionstake placein a loop or beforeor after the loop.The circuitry for this experiment (seeFigures5-17and 5-18)is quite simpleasis the code,which I call cPotTime.c.

Figure516

Pot rea(l ----

their accuracyand you couldhaveyariancesof up to 20 percent. Unfortunately,the rctimelunction isn't availablein the PICC Lite compilerlibrary of functions,and it can not satelybe programmedin by simplyusinga few C statementslike the lollowing:

Figure 5.117 Pot read circuit

RCPiflTRIS = 0r // Make RCPin an Output RCPin = 1r // C}rarge Capacitor (i = 0r i < onensr i++)t for // :i::"i:; RCPinTRIS = 1r // l4ake RCPin anal hput for (i = 0r ((i < fivems) && (0 != RCPin))r i++)t "i" contains a value ploportional // to the Resj.staltce

This is true for two simplereasons:the executiontime of the secondfor loop is not known and the returned valuefor i is proportionalto the resistanceof the potentiometer.If you havelooked at someintroductory PIC books,you may think this statementis wrong: many PIC bookspresentcodethat canbe usedto find the resistanceof a potentiometer,but the example codeand projectsin thesebooksare written in assembler whereeachinstruction(and the time requiredto execute)is known,not in a high-levellanguagelike C.

110

Figure 5.18 Breadboardwiring for the potentiometerreadcircuit

l , P 3 P I C @l l C l J E x p e n i m e n t s f o r

the Evil

Genius

When you look throughthe cPotTime.ccodeyou'll noticethat it waswritten without usingany variables. All the delaysare providedby TMR1, which is loaded with constantvaluesinsteadof the contentsof variables.I havenot explainedthe operationof the Capture modeof the ECCq becausewhenyou are first startingout, therearen't that many applicationslike

this one whereyou can take advantageof it. But you shouldbe ableto figure out how it and Comparemode work if you feel they havecapabilitiesthat you would want to take advantageol The lessonI want to impart with this experimentis that if you havea problem,it can often be solvedby looking at the datasheet.

Ul-Eenerating PtUM Experiment SisnalsUsingthe CEPand TMRa I

The PWM generatorfunctionbuilt inro the PIC MCU's ECCP is the latestand probablythe most andusefulpulsewidth modulation sophisticated (PWM) generatorthat I haveseenon any microconPWM generatordepartsfrom troller.ThePIC16F684's the typicaldesignby providingthe capabilityto intelligentlyinterfacedirectlyto high-currentmotor drivers software.As without interveninglogic or sophisticated I will showin a later experiment,it is an ideal basefor an intelligentDC motor controller.Thisexperiment, howeveris somewhatmore modest.It will simply introduceyou to the operationof the PWM generator hardwareand demonstratehow an LED's brightness canbe changedwith a PWM signal. Before explaininghow the PWM generatorworks,I shouldprobablyspenda few linesexplainingwhat a PWM signalls.A PWM signal(seeFigure5-19)consistsof a repeatingdigital signalin which the time on is variedto control the amountof power that passesto a device.PWMs are typicallyusedin DC motorsto control their speedbecausethey are much more efficient output power supply.Thetirue than a variable-voltage on is usuallyreferred to asthe duty cycleand is measured asa percentageof the total cycletime of the repeatingsignal. The heartof the PWM is the TMR2, which is a repeatingtimer driven by the PIC MCU's instruction clock.When enabled.this timer will count to the value

S e c t i o nF i v e P I C I t F h g q

LED

in the PR2 registerand then resetitseli TMR2'Soperation is controlledby the T2CON register(seeThble 5-12)andhasa prescaler,which dividesdown the which dividesthe incomingclock,and a postscaler, provide a delayedeventindiall to resetsignaldown, to usethe PWM postscaler is not required The cation. generator.WhenTMR2 is run in a PIC MCU that has a 4 MHz signal,a prescalervalueof 1:1,and PR2 equal ro 0xFF (255),the TMR2 (andPWM) period is 255ms (or 3,922kHz), The PWM generatorcircuit (seeFigure5-20)uses the resetcommandftom the PR2/TMR2magnitude comparatorto set the output in an RS flip flop.The currentvalueof TMR2 is continuallvcompared

PWMOn DutyCycle= PWMPeriod Fisure5-19 PwM

icrocontroller

Built-in

Functions

111

Table 5-? T?CONBegiEterDefinition

Ftc..Label

Function

7

Not Used

6:3

TOUTPS TMR2 Output Postscaler, 0b0000is a 1:1

Table 5-13 ECPIEONFlegisterBits Belatinsto the PIIJM6enerator Blts

Label

Funclion

7i6

P1M

PWM Output ConfigurationBits

Postscaler, 0b1111is a 1:16Postscaler

u, r-{

m

2

TMR2On

Must be setfor TMR2 to be operational

1:0

T2CKPS

TMR2 Prescaler

0b11for Full-Bridgereverseoutput (P1B Modulated,P1C Set,P1A/P1DReset) 0b10for Half-Bridgeoutput (P1A, P1B Modulated,P1C/PID Port Pins)

0b1xfor 1:16Prescaler

0b01for Full-Bridgeforward output (P1D Modulated,PlA Set,P1B/PlC Reset)

0b01for 1:4Prescaler 0b00for 1:l Prescaler

brt

0b00for Single(standard)output (P1A Modulated,P1B/P1OP1DPort Pins)

.r"i

CCI

5.4

DC1B

3:0

CCP1M ECCP mode selectbits

\r F

0b1111for P1A/P1C:/PlB/P1D Active Low 0b1110for P1A/P1CActive Low, P1B/P1D Active High

F g{

trt

Leastsignificanttwo bits ofPWM compare value

0b1101forPlA/PlCActive High,P1B/P1D Active Low

Figure 5-20

0b1100for PlA/P1C/P1B/P1DActive High

PWM block diagram

0b0000for CCP/PWM Off

l.{

"tJ d 11

0 $

13 II ?.,{


.-l

s

P..

X KT

againstthe value in the CCPR1L register,and when it is greater than the value in CCPR1L, the RS flip flop is reset.If the valuein CCPR1Lis greaterthan the value in PR2, the PWM output will alwaysbe high.This is what the basicPIC MCU PWM generator provides. But the PIC16F684hasadditionalcircuitryknown as the output controller, which can be usedto simplify the control of different types of motor controllers. In Thble 5-13,I havelistedthe relevantbits of CCP1CONas theyrelateto IhePWM generator. when I work with the PIC MCU CCP PWM,I generally work only with the most significant eight bits of the PWM Counters and ignore the two least significant bits.The extraaccuracyprovidedby the leastsignificant two bits is generally not required. In Figure 5-20,I imply that the PWM compareregister(CCPRIL) valueis comparedagainstthe valuein PR2.This isn't strictlythe case;the valueof CCPR1Lis bufferedand useduntil PRz is reset.Thisis done to ensurea larger valuefor CCP1RLis loadedin, causingthe PWM output to go high unexpectedly.To keep everything simple for your initial PWM applications,Irecommendthat you either passa single PWM signal from the module (on P1A, or RC5) or work with full H-bridgescontrolled asshown in Figure 5-21. When the UO pins are describedin the MicrochipPIC16F684datasheet, the labelsP1x (wherex is A, B, C, or D) are usedexclusively.To try and avoid some confusion,in this experiment,I haveincludedtheselabelsbut alsoincludedthe traditional pin namesaswell.

112

Motor Power

PlA (Foruvard Active)

P1B (Reverse Modulated)

Figure 5-?l

P1C (Reverse Active) P1D (Forward Modulated)

PWM full H-bridge contol

I realize that I have thrown a lot of information at you regardingthe PWM generatorbuilt into the PIC16F684, but it is actuallyvery easyto set up and work with. I will showjust how easyin the following expedment,which varies the brightnessof an LED accordingto the positionof the PICkit 1 starterkit's

l , A 3 P I C @f l C U E x p e n i m e n t s f o r

the Evil

6enius

potentiometer. Unfortunately, none of the PWM outputsare connectedto any ofthe LEDS on the PICkit 1 starterkit, and,further complicatingmanners,P1A (RC5) is not available on the PICkit 1 starter kit's inline socket.Fortunately,RC2 (P1D) is closeto the socket'sgroundpin, so you put an LED into the PICkit 1 starterkit to demonstratethe operationof the PIC MCU'S PWM by varying the perceivedbrightnessof the LED. In this experiment,I wantedto take advantageof cADC.c, which readsthe voltage coming from the PICkit 1 starterkit's potentiometerbut alsodisplaysit as a binary value on the eight LEDs. A single LED can be wired from RC2 (P1D) to groundon the PICkit 1 starterkit (seeFigure5-22)to demonstratethe operation of the PIC16F684's PWM generator.The code written for the application (cPWM.c) is quite simple, with the only additions to cADC behg the TMR2 enable,the PWM enable in full-bridge output forward mode,andthe ADCValuereadby the PIC MCU's ADC passedto the PWM valueregister(CCPIRL). *includle CPWU - Dia!,lay /* r! LED Brightnesa

lhe PICkit Level

Pot

Input

Value

ADCSlale

iat iat

= 0,. ADgvalue Dlay = 53,

//

of ADC

tr1

X

r,ED Tlm€ oa D€lay variabl€

F?{

= {0b010000, 0b100000, 0b010000,0b000100, 0b100000,0b000100, 0b000100,0b000010], conBt cha! TRIgAValue [8] = {0b001111, 0b001111. 0b101011,0b101011, 0b011011,0b011011, 0b111001,0b111001)t const char NOTPORIAI8I = lO, O, O. O, O, O, O, Ojt conal

nain(

char

P O R T A V a I U e[ 8 ]

E'tr'.a of.f

//

ANSEL = l.t // .tuat ADCONo = 0b00000001, // Turn // BiE // Bil // BiE / / BiE // BfE ADCON1 = 0b00010000,

Colllrarators

RAo is on 7 6 4r2 L 0 -

an Aralog

F{

7V

the Alc .tuEtified Left Itae ltDD - Channel 0 Do dot Stalt Turn on ADC lh€ // Seldrct Eoac / I

s

Input

F

S.np1e

, I

Clock

aE

EaabLe PwM with Active Eigh No Tura on/off Delay ttake RC2/P1D OutDuts Active

Ptcu].coN - Ot ll TRISC2 = O, ll -

0x040, //

Stall

//

PWU at

Iatellnedliate

&

TU P1D

//

Loop

F"t vt

valu€

& & == 1)

6) t-t

Eh€ Ful1 Range // I'uR2 on wltsh No PrescaLe!

ccP1coN = 0 b 0 1 0 0 1 1 0 0 r

whil€(l.

}J.

.'ts

PORTI = 0t CltCoNo = 7r

CCPR1IT

$

t1

F)

)

t

PR2 = 0x0EF, // wolk T2coN = 0b00000100r

pletlko

( INTIO & IID1IDIS & PIIRTEN & IICIJRDIS -CONFIE I'NPROIECT \ & IINPROTECT & BORDIS & IESODIS FCMDTS ) t

// ' KeeD rrack Operation

aB

Thia Drogram aarq)leg the voltage oa RAo uElrlg lhe ADc ana DiaDlaya lt usl.ng a Pwtt va1u6 on trP1Dn (RC2). ThiE Program ia ale8lgn€al fo! the rryk6

= 0t

iDt

Foieve:.

,-, " }{

q

t ints i,

j,

kt

f , o r ( i = 0 r i < 8 r i + + ) / / Loop through Each of, lhe 8 I,EDS | for (j = 0t j < DIaYt j++)t // Diaplay tron" Delay lJoop if ( (aDcvalue & (1 << t)) == 0) PORIA = NOTPORTAIiIt €1Ee PORTA= PORtAValue [L] , TRIIIA e TRISAVaIlle lil t , // rof ErtrlEch (A.DcstaEe)

//

ADc staEe uachine

t

Fieure 5-?? LED anodewired into the PICkil I starter kit connector at RC2 (third pin from bottom) with its cathodewired.to ground (bottom pin)

caBe 0: star! N€xt salllrl€ // Finiaheil, GODONE = 1, ADqgtat€++i breakt caEe 1: for ADc tso conDlete / / wait ( lGoDoNE) if ADCState++t // S€mp1e Finishetl break; case 2: // Sav€ SarDLe Value in nADCVaLu€tr = ADRESII, ADcltalu€ .e.Dcgtat€ - 0; breakt , / / rLcEiwa

S e c t i oF n i v e P I C I h F h A Tl + li c r o c o n t r o l l e n B u i t t - i n

Functions 113

ry ,Zt

td Ft

&3 F,. € tsa

gr #3

) l

I . = ( k + 1 ) % 1 0 t

//

Irl)date

(0 -= k) if CCPR1IJ = ADCVaLue,

//

sinply Change the PWM Value to Change the I.ED Output'

PVIM Every

100

// elihw // Enat cPl'Dl

Two pointsshouldbe notedaboutthis application. First,becauseI decidedto usethe full-bridgeoutput modeof the PWM generator,pins RC5 (P1A),RC4

(P1B),and RC3 (P1C)cannotbe usedin the application. If this werea stand-aloneapplication,I would recornmendthat you use the single-outputmode of the PWM generator(CCPICON loadedwith 0b00001100) and the LED connectedto RC5 (P1A).Thesecond issueis that whenI simulatedthe application(in MPLAB IDE version6.60),therewasn'ta CCPR1L registeravailable;insteadtherewasa CCPRL register, whichperformsthe samefunction.This discrepancy will orobablvbe fixed in later versionsof MPLAB IDE.

ExperimentU2*5toring and Fletrieving Dat a Us in gEE PF OMMe mo rg EEPROU_WRITE(unsigneat cha! ulsigneal ehar EEPRouData) i

An often overlookedfeatureof the PIC MCU is the EEPROM datamemorythat is built into the flashbasedchips.EEPROM is an acronymfor electrically programmableread-onlymemory.In the PIC erasable MCU, EEPROM consistsof a numberof bytesthat canbe written to with the expectationthat the value written will still be therewhen the chip is powered down and then poweredback up sometime later.This expectationcannotbe madeof the staticrandom accessmemory(SRAM)-basedfile register'sthat loosetheir valueswhen the PIC MCU is powered down.EEPROM datamemory(often referredto as srmplyEEPROM) rs callednonvolatile to indicate that it retainsits contentsevenwhenpowereddown.Not surpdsingly,the SRAM-basedfile registersare saidto be volatile.The flashprogrammemoryusedin the PIC MCU is a variationof EEPROM with sliehtlvdifferent operatingcharacteristics. To accessthe EEPROM datamemory a seriesof assemblylanguageinstructionsare used.Fortunately, the PICC Lite compilerprovidestwo library functions that can be usedto read and wdte the EEPROM. Their prototypesare asfollows: (unaign€al unsign€al cha! EEPROM,REA.D EEPROMAdItITeSs ) ;

114

EEPROltIAalalresE,

The PIC16F684has256bytesof EEPROM while the PIC12F675has128bytesof EEPROM. Therefore, the maximumEEPROMAddressis 0xFF and0x7Ffor the PIC16F684and PIC12F675, respectively. The data valueis a full eightbits,which meansthe valuestored at eachEEPROM locationis in the ranseof zero to 0xFF (255decimal). The typicalusesfor the EEPROM includesaving calibrationvaluesor savingconstantsinsteadof creating constants.To demonstratethe operationof the EEPROM,I createdcEEPROM.c,which will initialize the EEPROM memoryof a PIC16F684with a standard pattern (0x00,OxFF, OxAA,0x55)so that on subsequentpower on cycles,the storedvaluewill be recognizedasvalid.The valueat the next address(or zero if this is the first power cycle)will be displayedon the eightLEDS of the PICkit 1 starterkit.When the button is pressed,the ADC will be read and the value will be displayedon the LEDs, and whenthe button is released,the ADC valuewill be storedin EEPROM for the initial displaywhenthe PIC MCU powersup. *incLude CEEPROM - Display /t if Butston Preeseal

the

Saveal EEPRO!{ Value/llDc

Thia program Displays a gaveat EEPROM value ItnleEE th6 Button on RA3 is D!€ss€tl and then the a.DC is Displayeal. When the Button is Released, the ADC Value is Saveal in EEPROM. Thia coale is baseal on ncADc.cr. ttvke prealko o4.12.20

cha! -CONFIG

( I1!:!IO

& WIITDIS

l , e 3 P I C @l ' l C UE x o e r i m e n t s f o n t h e E v i l

& PWRTEN & !'ICIJRDIS &

Genius

I'TVpROTECT\ FCUDIS) t

InI int irlt int lnt

& IJNPROTECT & BORDIS & IESODIS

I, J' AItCStsat€ = Ot ll KeeD Track = 0t ADgvalue = 0i Buttsonstat€ Dis91ay, olalDisDlayt

of

&

Lf

ADC Ol,€ratioa

{

7 5 4r2 L O -

ADcoNl = 0b00010000, if

Inpu!

// T.Irln on lhe IJeft iluslif,iedl Use vDD - chaDnel 0 Do nol SlarE tnrrn on ADC

ADC Samlrl€ ) I

// soromct the clock as FoEc/8

((0 == EEPRoT'r-READ ( o ) ) && ( o'rFF == EEI'RorrREAD(1)) &&

(4) r Dispray = EEPRoM-READ

( 1 , onEr ) r EEpRo!'r,wRrrE Ox55) '

= 0t

== 1)

//

Loop

Forever

t f o r ( i = 0 r i < 8 r i + + ) Each of th€ I { / / Loor, thlough (j = 0, j < Dlayr j++), for ll Di-Bp lay "On" D€Iay l,oop ( (DiBpIay & (1 << 1)) == 0) if PORTA = NOTPORTAIiI t elg€ PORTA = PORTAVaIUe [i] t ARISA = TRISAVaIU6 lil t j Eof ll

X

trd

0

r-{ F.

{0

Ft

l& t\ I

I

en

To test the application rather than continually plug the PICkit 1 starter kit or the PIC16F684 in and out. you can control the power to the PIC device in the plCkit 1 starter kit by clicking on,.programmer" and

PIC MCU'S RA4 pin.

( 3, o,rAA), EEpRoM_wRrrE EEpRoM wRrrE({, o)r // No rnirial

while(1

- Displayt oLtlDiaDlay = Ii Buttonstate DiaDl.ay = ADRESET ADCgEate = 0t breaki // hctiwg ) // elihw // Entt clDc

that comesup will giveyou the option of turning on or off the power to the PIC MCU in the PICkit 1 starter kit's socketaswell aspassinga 2.5kHz clockinto the

;t"" (o, o) , EEpRoM-wRrrE

Diaplay

tql

F.t

thenon"Properties"intheMPLABlDE.rhewind lsa

l3lfi ==ll|l!il_ffili]i,*

E E P R O MW R I T E ( 2 ,

R€leaseal

ADcgtsat€++t broaki case 1: // WaL1cfot }DC to cornplete if ( lcoDorrE) ADcstate++r // sarE)le Finishedl bt€akr case 2. // Save sarq)le velue in trADcvalu€n if (0 -- Buttonstale)

In in( )

AItCONo = 0b00000001r I / BLE // Bil ll Bi,E / / Bj.E / | BiE

Button

GODONE = ]'t

0b011011, 0b011011, 0b111001,0b111001)r conat char M)rPORTAISI = {0, 0, 0. 0, 0, 0, 0, 0}t

T.lrrd off comparator8 .fus! RAo is an Ana1og

//

| ll fi } €Is€ // Button PreEs€al Ewilch (nlrcSlate) // ADC State Machine t case 0: // riaiBh€al, gEar! Next SsrDIe

0b101011,0b101011,

// //

!= RA3)

A.Dcgtale - 0t // Resel .e.DCOperation (0 != Butlonslate) if HaE AI'C // Diaplay value ( EEPRO!{_!fRITE ( 4, Disl)lay), DLaDlay - OlalDisDlayt = 0i Buttonstale

iat Dlay = 53i // LED Tine on D€Iay varlable conet cbar PORTAvalue [ 8l = {0b010000, 0b100000, 0b010000, 0b000100, 0b100000, 0b000100, 0b000100,0b000010)r conat char TRISAVaIUe [8] = {0b001111, 0b001111,

PORTA = O' C!|CON0 = 7, .aNSEL = 1r

(0

IJEDS

value

s 5

To test this application, burn the cEEPROM.c code into the PIC16F684 and let the PICkit l starter kit exe-

cute as it would normally. Next, pressthe PICkit 1 starterkit's button and turn the PICkit 1 starterkit's potentiometer to somevalue (which will be displayed on the PICkit 1 starterkit's eightLEDs). When the button is released,the power up valuewill be displayed,but after cyclingthe power on, the PICkit 1 staderkit the PIC16F684will displaythe valuepreviouslysetinto the EEPROM usingthe buttonandthe

potenbometer.

41-

F r'n ht t"r, fia

ly

\

r,,.

H *J !'.l

F-t \J $! -* n! i4

S e c t i oF n i v e P I C l , h F h A qH i c r o c o n t r o l l e r B u i l t - i n

Functions 115

Section

Six

InterfacingProietrtsfor the PIC@ Microctrntroller

DMM NeedIe-nose

plie!s

B!eadboa!d Wiling

I

Plc16F68 4

470f) resistors

I

7451383to8decoder

100f,1 resistors

1 74LS174 hex D fLip

flop

2 0.01 pF capacitors

2N3906 PNP transistols 1 fwo-line,

16-colulrm

I

Seven-seghent displaY

lk

svritch matrix keypad with an eighto! nine-pin breadboa!d inte!face

LCD

1N914 (1N4148) silicon

1 Seven-row, display

(any type)

1 16-button

1

coilnon

1 Dual seven-seghent LED display

kit

diode

corlnon

five-column

LED

cathode

ano
LED matlix

Breadboard-mountable push button

1 Three-cell 1 Two-cell

AA battery AA battely

3 AA alkaline

resistor

Before I start demonstratinghow the PIC MCU interfacesto other digital electronicchips,I feel it would be usefulto reviewthe basicsof digital logic andnote someof the important characteristicsto keep in mind when you are creating applications with the PIC MCU There are literally dozensof different logic technologies, eachwith differentoperatingcharacter-

Breadboard-mountable SPDT sw j.tch (E-Switch EGl903 reconanended) momentary

On

pack pack

battelies

istics.I've listedthe mostpopular onesin Thble6-1. For the different varieties of TTL, C,AC, and HC/HCT logicfamilies,the part numberstartswith 74, and the 4000seriesof CMOS chips have four-digit part numbers,startingwith 4.Table6.1liststhe characteristicsof the different types of logic chips you will want to work with:

',17

Table 6-1 Digital LogicTechnologiesuith ElectdcalCharacteristic-5 thlp Tcpe

VT

r!

H F,r.{ htr "t{

tl

6

t!F{

ti $ .&,r X t"J

I

X

.*l

n '.'d t l

dll

PoLuerSupplg

6ate Delag

lnput Threshold

O Dutput

I Output

Output Sink

vdd - 0.7

25 mA

3.3V

\2 nA

3.4v

5mA

3.4v

8mA

3.4v

40 mA

Vcc-2V VcN- 2V

20 mA

3.5V

20 mA

PICMCU

Vdd=2to5.5V

N/A

50% vdd

TTL

Vcc : 4.5 to 5.5V

8ns

N/A

LTTL

Vcc - 4.5 to 5.5V

15 ns

N/A

LSTTL

Vcc : 4.5 to 5.5V

l0 ns

N/A

STTL

Vcc - 4.75to 5.25V

5ns

N/A

AS TTL

Vcc : 4.5to 5.5V

2ns

N/A

ALS TTL

Vcc = 4.5to 5.5V

4ns

N/A

FTTL

Vcc = 4.5to 5.5V

2ns

N/A

0.6v 0.3v 0.3v 0.3v 0.5v 0.3v 0.3v 0.3v

c cMos

Vdd=3to15V

50 ns

0.7Vcc

0.1Vcc

0.9Vcc

3.3mA*

AC CMOS

Vdd=2to6V

8ns

0.7Vcc

Vcc-0.1V

50 mA

HC/HCT

Vdd=2to6V

9ns

0.7Vcc

Vcc-0.1V

25 mA

4000

Vdd=3to15V

30 ns

0.5vdd

0.1v 0.1v 0.1v

vdd-0.1v

0.8mA*

Tt1eoutput sink ctfrrentsare specifiedfor a power voltageof 5 volts If you increasethe power supply voltageof the indicatedCMOS parts(notedwith an asterisk),you will also increasetheir output cunent sourceand sink capabilitiesconsiderably. In this table,I markedTTL input thresholdvoltage asnot applicablebecauseTTL is current driven rather voltagedriven.You shouldassumethat the current drawn from the TTL input is 1 mA for a 0 or low input. CMOS logic is voltage driven, so the input voltage thresholdspecificationis an appropriateparameter. Knowing that eachTTL input requires a current sink ofjust over 1 mA and mostTTL outputscansink up 20 mA, you might expectthe maximumnumberof TTL inputs ddven by a single output (which is called fanout) to be 78 or 19.The actualmaximumfanout is eight to ensurethere is a comfortable rnargin in the output to be ableto pull down eachoutput in a timely manner.Practically,I would recommendthat you try to keep the number of inputs driven by an output to two but neverexceedfour. Somedifferenttechnologiesthat you will work with do not havethe sameelectrical drive characteristics andmay not be designedto pull down eightinputsof anothertechnology;so, to be on the safeside,alwaysbe very conservativewith the number of inputs you drive with a single output. The output current sourcecapability is not specified becausemany earlychipswere only ableto sink current. This wasall that was required for TTL and it allowed extemal devices,such asLEDs to be driven from the logic gate'soutput without any additional hardware,andit simplifiedthe designof the first MOSFET:basedlogic chips.The asterisk(*) in Table 6.1 indicatesthat the sink cuffent specificationis for 5 volts of power; changingthe power supply voltage will changethe maximum current sink capability aswell.

118

8mA

There are threebasicoutput types:totem pole,open collector, and the tristate driver, which is presented later in this chapter.In caseswheremultiple outputs are combined,different output t)?es shorj'ldneverbe combineddue to possiblebus contention. The TTL output (seeFigure 6-1) is known asa ntem pole outputbecauseof its resemblanceto its namesake.If you were to connect a totem pole output to a TTL input and measurethe voltage at the input or output pins,you would seea high voltage,which the gate connectedto the input would recognizeas a 1. When a low voltage is output, the TTL gate will respondasif a 0 wasinput.What you are not measuring is the current flow between the two pins.

"High" Output Control Current

Output Pin,Can EitherSource orSink Current

"Low" Output Control Current Figure 6-'l

l , P 3 P I C @l l C l JE x o e r i m e nt s

for

TTL totempole output

the Evi I

Genius

Output Pin,

EffectiveOperation Sional ,^-__,,,

NPN

Output Control Current

ulrpu

_-,-

<j"'p"r

"'

I

I Tn-gate Conirol

Transistor CanONLY PullPinto Ground

LogicSymbol

t,:,!

Figure 6-a

TTL open-collectoroutput

Thereis anothertype of output that doesnot source any currentand is known asthe oper?collector(or open-drainfor CMOSlogic) output (seeFigure6-2). This output typically hastwo uses.The first pulls down voltagesthat are greaterthan the positivevoltage appliedto the chip.Normally thesevoltagesare less than 15V and cansourceonly 10 to 20 mA. For higher currentsand voltages,discretetransistorsmust be used.The seconduseis for dottedAND bussesin which multiple open-collector/open-drain outputsare tied togetherwith a singlepull-up-the output is at a high-voltagelevel aslong asall the output transistors are off. Totempole outputsare the recommendeddefault gateoutput becauseyou caneasilycheckvoltagelevels betweenintermediategatesin a logic string.You cannot usea volt meter or logic probe to checkthe logic levelsif a TTL gateis driven by an open-collectoroutput.Additionally,if a CMOS input is connectedto an

Figure 6-3

Tri-statedriver

i'i'i

open-collector/open-drain output then therewill be no high voltagefor the gateto operate.An open-collector/open-drainoutput can be usedwith CMOS inputs if a pull-up (typically10k in value)is addedto the ouf put.The only caseswherean open-collector/opendrainoutpulshouldbe usedis whenyou arewiringa dottedAND gateor are switchinga power supplythat is operatingat a voltagedifferentfrom the gate's power.

:-*1

:.

The third output type,the tri-statedriver, can nol only sourceor sink currentbut can be turned off to electricallyisolateitself from the circuit that it is connectedto (seeFigure6-3).This type of output drivers is usedon the PIC MCU IiO pins. Exceptin the conditionof open-collector/opendrain driversbeingusedto ddve CMOS inputswithout a pull-up resistor,thesethreeoutput typescanwork with all of the digitallogic inputslistedin Table6-1. t-;:.

Experimentq3 - Drivinga Seven-SegmentLEDDisplag Directlgfrom the PlElSFEBq P rc 16!'68 4

;,.€

Seven-segrmeot common cathode LED display 0.01 pF capacitor tYpe )

(any

Breadboa!d-mountable (E-Switch SPDT switch 8G1903 recomnended) Two-cell pack DMM

AA battery

AA batteries

Needle-nose pliers Breadboard Wiring

S e c t i o n5 i x

kit

Interf acing Projects

f or

t h e P I C @t l C U

t-ri

119

h'r' t'fi

ai,1

I found this experimentto be very satisfying.In about a half-hour,I wasable to make it displayeachof the 10 digitson a seven-segment LED, with a half-second delayin between.This includedmodifyingcodethat I stolefrom other applicationsto executethe application finding out the wiring wasnonstandardon the seven-segment LED I usedfor my prototype.I expect that you will be able to createyour own versionof this applicationand seehow easyit is to createa usefuldisplay usinga singlePIC microcontrollerin short order. The basisfor the experimentis the seven-segment LED display(seeFigure6-4),which is normallywired rn a commoncathodeor commonanodeconfiguration. The schematicdiagramfor the seven-segment LED displayin Figure6-4showshow a commonanodedisplay would be wired.Even if you havea nonstandard LED display(asI have),you canplot seven-segment out the commonpins and the pins for eachsegmentin just a few minutes. The basic10 digitscanbe displayedby turningon the LEDS for the differentsegmentsasshownin Figure 6-5.Additional characterscan be producedusing differentsegments. Although other than the six most significanthexadecimaldigits (A, B, C, D, E, and F), you will be hard pressedto comeup with all the alphabeticcharactersthat look good on this display(for example,M). The liquid crystaldisplay(LCD) display discussed later in this sectionis a much better tool for this task. The circuit for this application,not unexpectedly, poweredby two alkaline consistsof a PIC16F684, radio batteriesand driving a seven-segment LED display (Figure6-6),and can be wired very simplyon a breadboard(Figure6-7).Theactualcircuit is very similar to othersthat you havecreatedalthoughwith a different LED display.Simitarly,the applicationcode (cTSegment.c) shouldnot hold any surprisesfor you.

7-Segment LED

Figure6-6

Figure 6-7 Singleseven-segment LED experiment circuit on a breadboard

*incluale c?SegmenE.c - RoIl /* Segment LED Diaplay

':

thlough

10 Digits

on 7

Thia program will each of the Decilra1 aliaplay dligilB on a 7 Segmen! Cormon Calhodle LED Display. Earalware

3

Seven-segment L E D circuit

aA5 RC5 RC{ RC3 Rc2 Rc1 Rco

-

Notes:

Segment a Segrnent b Seg:nent c Segment tl segment e seqment f gegment g

nl'k€ pr€ilko 0{ . 11. 10

Figure 6-q

Seven-segment LED display

*/ CONFIG(ITVIIO & I'IDTDIS & PWRTEN & MCLRDIS & IINPROTECT \ & UNPRCTIIECT& BORDIS & IESODIS & FCIIIDIS) t

int codst

i,

i, char

kt LEDDigit

Fiqure 5-5

Seven-segment numbers

L20

l , e 3 P I C o l l C l JE x o e r i m e n t s f o n t h e E v i I

t10l

= {

6enius

10

// RRRRRRR - PIC15F584 Pin // ACCCCCC / I 554321-0 - LED Segmonl abcdef,g // 0b1111110, 0b0110000, 0b1101101, 0b1111001, 0b0110011, 0b1011011, 0b1011111, 0b1110000, 0b1111111, ob1].11011) t

fo! (i = 0r i < 255r i++) // for (j = 0r j < a29, j++\, DLgit Digtt Digir Digit Diqit Diqit Disit Digit Disit Disit

// // // // // // // // // //

zeto One rwo Three Fou! Five Six Seven Eight Nine

nain ( )

t PORTA = 0, PORTC = 0, C!|CON0 = 7, ANSEIJ - 0, TRISA = 0b01U11; TRIsc = 0b000000t

k = 0r $ht1e(1

--

!>

Conparatsora / / TIlxIL oft // Tuln of,f, tlDC // RA5 iB an Oulput // A1t BibB of PORTC are olrtputa al

Digits

//

Starl

//

Loop Foreve!

0

RAs= LEDDisi![k] >> 6, // PORTC = rEDDisittkl

k = (k + 1) %10, l ,

Sinll'le Delay l,oop

Ld

li;"??!"

"t"" ""

& 0x03F,

,,

llillil"olr*,"nr" i-r

// ellhv // E'rdl cTgegmenl

In the applicationcode,I do want to point out that I storedthe digit pattemsin a 10-elementaray and that I tried to make the bit specifications assimpleaspossible for the programmer(includingmarkingthe segment lettersand the I/O pin over eachbit of the array).With only sevenwiresrunningfrom the PIC MCU to the display,I felt I could work at making the program assimple aspossiblefor the programmer to coffectly define the set pin outputs required for each disit.

: :!.;4

r.

Experimentqq -

MultipleSeven-SegmentLEDBisplags

'tl

n Prc16F684 2N3906 PNP tlansistors

L

Dual seven-segmedt commo!! anode LED display

i

1o o,f) resistols 0 .01 FF capacitor tYpe)

(any

B!eadboa!d-mountable (E-Switch SPDT switch 8G1903 recornmended) Needle-oose

plj,ers

Breadboa!d

Two-cell pack

Wiring

AA alkaline

kit

There are a number of ways to add multiple seven-segment LED displaysto an application.You could route seven(or eight,if the decimalpoint is required)PIC MCUs to eachdisplay.You could use a comrnercially availableseven-segment LED driver chip (the7447is most commonly used) for eachdisplay.You could also usea commerciallyavailablemultidisplaycontroller

S e c t i o nS i x

p

battelies

chip (suchasthe MAXIM MAX7219). Or you could programthe application'sPIC MCU to sequence throughthe displays. The latter methodis surprisingly easyto do and involvesthe leastamountof hardware. Thereare a coupleof pointsthat you shouldbe aware ol however,that I will presentin this experiment.

Inten fac i ng Proj ects

for

. t )

AA battely

t h e P I C @t l C u

L2t

t

The first is,you cannotdrive the commonanodeor cathodepin usinga PIC MCU I/O pin.The PIC MCU I/O pin cannotsourceor sink enoughcurrentto light all sevensegments. Instead,I usea commonNPN bipolartransistorfor commoncathode(seeFigure6-8) displaysor a PNP bipolar transistorfor common anodedisplays.These transistorscan be controlledby either a PIC MCU IiO pin with a proper base-currentlimiting transistoror by a data-selector logic chip (asI will showin the next section).You might be surprised to discoverthat commonanodedisplaysare most often usedbecausethey can be usedwith 74xr series logic data-selectorchipsand PNP bipolartransistors. To sequencethroughmultiple seven-segment LED displays,the controllinginterfacedeviceoutputsthe valuefor a speciticdisplaywhile enablingonly its common pin transistorasshownin Figure6-8.Togive the appearancethat all the displaysare activeat the same time and avoidflickering,you mustrun throughthe entire sequenceat least50 timesper second.This meansthat for the four seven-segment displayexample,eachdisplaycan be activefor a maximumof 5 ms To demonstratethe operationof multiple sevensegmentLED displays,Icreatedthe simplecircuit shownin Figure6-9.I havenot beenspecificon the type of dual commonanodeLED displayto use becausequite a bit of varianceexistsin differentpafis and you may find someinexpensiveonesthat are wired differentlythan the standarddisplays.Alldisplaysshouldhaveconnectionsfor the segmentsaswell ascommonanodesfor eachdigit display.Thedisplays that I usedwire a singlepin to eachsegment,necessitatingtwo connectionsfor eachsegment,which resultedin the rather messywiring of the circuit as seenin Fieure6-10.

r,m

ffi Figure6-9

Dual seven-segment LED circuit

Figure 6-10 Breadboardwiringfor clualsevensegmentLED displaycircuit

#incluale - Ro11 through c2*?Seg.c /' 7 Segment LED Display

15 DigitE

ThiB program nri11 aliBplay each aligits on two 7 Segm€nt Codfiron Displays.

Second

The codle/wiling that Nesativ€

---'-----*

Eardlware

I

1 <-

aA5 RC5 RCll RC3 RC2 RC1 RCo

-

Segment Segnent S€gment segment Segnent Segiment segment

ThirdDigitDisplayed

is baseat on "cTsegment.c'i Activ€ LED wiring is useat.

a b c tt e f g

7 segment 7 segment

Display Display

Inyke prealko 04.42.09

Figure 6-8

Multiple LED operation

L22

l,El PfC@ CU Exoeriments for

orl a Dual

of the Her. 15 Cathoal€ LED

Notes:

Right Ireft

FourthDigitDisplayed

ffi

Dual 7-SegmentCommon AnodeLED Display

the Evil

6enius

Noting

( Ilvrlo & v{EtlDIs & P!{R!EN _coNrlc I'NPROTECT \ & I'NPRCIIIECT & BOBDIS & IESODIS

L, j, DisDlal^Ialue,

l'at iat

& MCLRDIS

RA5 = r,EDDisit [ (Diapla]ryalue >> {) & 0r0Fl >> 5t PORlrc = IrEDDigtt t (Dl.ap1ar/Va1u€ >> 4) & 0x0Fl & 0x03F, | // fi TRISA = TRISA ^ 0b0111ur // Sloap leftlBighl PORTA = PORTA & 0b1U100, // Make gure BitE

&

& FCUDIS) '

DisDLeylEDt = DisDIayIrED

DiEplayLED RRRRRRR

//

NoPOr for (i

= 0t Di aplat4lalue = 0i DiapIaYLED == 1)

// ll // //

NoPO, l = j + 1r (25 == j) if

// //

i

Errt *, }

DI'LE

/ / U s e f l f o ! 1 0 m a Tinids < 550, i++)r / / 10 ma Delay IJoop / / u s e i l f o r 1 0 m B Tining

= 0r

t_*

-

p

Inc!€menl th€ counler? 1/4 Seconal Paaaeal?

Diaplayvalue++t j I ] |

{ PORTA = 0, POREC = 0, CMCONo = tt ANSEIJ = 0, TRISA = 0b011101t TRISC = 0b000000;

oE}ret Ne'I!

t d

t

nain ( )

$tra| of,.f Cornpalatola $)zn otf. AN R}5/RA1/RA0 are OulDuta Alt BitsB of POBTC are Outputa

// //

DiBplayl.ng Stalt at DlB!,lay lhe 1a fLrat

//

IJooP Forever

0x00

{ if

//

LEDDigit tl = { - PIC16F58{ Pin

/ / 5543210 // abctl€fg - r,ED segmellt 0b0000001, 0b1001111, 0b0010010, 0b0000110, 0b1001100, 0b0100100, 0b0100000, 0b0001111, 0b0000000, 0b0001100, 0b0001000, 0b1100000, 0b0110001, 0b1000010, 0b0110000, 0b0111000)t

while(l

^ lt

t l t

(0 == DiEDlayrJED)

{ RA5 = IJEDDigir lDiaDla]ryalu€ PORTC = rJEDDl.ltLr[Dlsplat/Value

& 0x0Fl >> 5, & 0x0F1 & 0x03r',

Increm€nt lhe counler another 1/4 geconal //

= 0t // rte3el // 1A // elihw // E^d. c2x?Seg

for

The basicapplication,incrementingthe displayonce every 250ms to count from 0x00to OXFF,is quite simple and is calledc2xTSeg.c.There really shouldbe no surpdsesin the codeother than the fact that segment valuesfor eachbit are reversedfrom cTSegment.c becausethe PIC MCU are connectedto the display's cathodesinsteadof anodes. The two NOP0;instructions aroundthe final for loop wereplacedthere to giveme somewhereto break and to ensurethe applicationdelayed10ms,givinga 50 timesper second update speedfor the two displays. After creating c2x7Seg.c, I thought it would be fun to comeup with a czxTSegPc in which the lightedsegment seemsto run aroundthe two displays. These typesof displaysare quite easyto write and a lot of fun to watch.After watching this, I can't help but think theremustbe a simplegraphicalgamethat couldbe createdusingseven-segment LED displays.

!

's l 1

p'

ffi 41X

r*,t

) eLse

tsr€

-.{: tt*

S e c t i o n5 i x

Intenf acing Projects

f or

t h e P I C @l l C U

L23

r-15-LEDMatrixDisplags Experiment

1 Plc16F68 4 1 74SI383to8decoder t

Seven-!ow, LED display

five-col,umn

4?OO tes istols 0.0I pF capacito! tYpe )

B!eadboa!d-mountable (E-Switch SPD! switch 8G1903 reconmended)

Needle-nose plie!s

thlee-cel1 pack

B!eadboard Wiring

kit

Seven-segment LED displaysare excellentfor displaying numericdata,but whenyou havecharacterdata, their usefulness reachesthe end very quickly.A number of differenta/phanumericLED displzysexist.The mostbasictype is the 14-segment LED display,which is similarto the seven-segment displaythat you just experimentedwith. However,due to the specificposilions of differentsegments, it's difficult to make all the differentcharactersrecognizableon a 14-segment display.T\e dot-matrix LED display allows arbitrary charactersto be displayedwhile usingfewer I/O pins than the 14-segment LED display,but it requiresmore work to useand plan how to build your characters. The dot-matrixLED display(whichI calljust an LED matrix) consistsof a numberof LEDs arranged with their anodesand cathodesasshownin Figure611.By pulling a columnconnectionto positivevoltage, individualLEDs canbe lit by connectingthe appropriate row anodesto ground.For this experiment,I useda 5-columnby 7-rowLED matrix,but if you look around,you will discovera numberof differentsizes are available.Regardlessof their size,they will be driven usingthe samemethodologyasshownhere. Using a 4700 resistor,the batteryclip,and a couple of wires,you canfigure out the wiring of your display.I startedby connectingpin 1 (the top left corner)to negative voltageand then scanningthe pins to try and identify the sevenanodes.I wasnot successful at light ing any LEDs, so I repeatedthe procedurewith pin 1 connectedto positivevoltage.OnceI startedgetting LEDS to light,it wasa simpletask of identiflng the functionsof the variouspins andmappingthem out on

L24

(any

AA alkaline

AA battely batteries

a sheetof paper.In doing this,I discoveredthat the rowsconsistedof the LED'S anodesand the columns werethe LED'S cathodes. The 5X7-LED matrix displaythat I usedrequires 12pins to operate;althoughthe PIC16F684is quoted ashaving12 I/O pins,it actuallyhasonly 11 I/O pins and oneinput pin. RA3 can only be usedasan input, so to take advantageof all 35 LEDs of the matrix that I used,I had to comeup with someway to multiply the

Row 0 Row 1 Row 2 Row3 Row4 Row 5 Row 6

Col

Col

Col

Col

Col

Figure 6-11 LED matrLr

l , E 3 P I C @I ' l C l JE x p e r i m e n t s f o r

the EviI

Genius

umn of LEDs is wdtten at the sametime and eachcolumn is scanned.This is similarto the dual seven-segment LED displayexperimentand givesthe appearancethat eachcolumnis activeat the same time.cMatrix 2.cruns throughthe first four characters of tlie alphabet.

5x7LED

-: - --r-

#includle 2.c - Display cMatrix /* r,ED DiEplay

Soine Letlera

on 5x7

l

I

74L5174 Figure 6-l?

MatrLrcircuit

numberof operationalpins.In this application,I used a 74S138decoderto providethe columnnegative power supplyselect.The selectionof the S technology decoderwasselectedover the more commonLS technologyto sink the mostcunent (LEDS fully lit) aspossible.This allowedme to usethreepins to select betweenfive columns,requidnga total of l0 pins to control the LED matrix.Thecircuit that I cameup with for this applicationis shownin Figure6-12.Note that I tried to arrangethe wiring in sucha way that the anodes(rows)are all driven by PORTC (with the seventh bit beingpassedto RA4), while the cathode's (columns)pull-downdecoderis selectedby the three leastsignificantbits of PORTA.

8A0-Decoale!0gelect RA1 - Decoale! 1 Select Rt2-Decoaler2Select aA{ - Anoale 5 Rco - Anoale 0 Rc1 - A$oale 1 Rc2 - Alotl€ 2 Rc3 - Atroale 3 Rc{ - Alotl€ 4 Rc5 - Anoit€ 5 nyke predko 04 . 12. 04

& WDTDIS & PWRTEN & MCLRDIS & -CONFIG(INTIO UNPROTECT \ & UNPROTECT & BORDIS & IESODIS & FCfiDIS), int

i,

const

j, char

k,

n,

Dlay,

lJ€ttsers[]

CurLettert = {0b1111110,

Start

//

0b0010001, 0b0010001. 0b1111110, 0b0000000. 0b1111111. //

To testout my mappingof the LED matrix and how presumed I to wire the application(seeFigure6-13),I createdcMatrix 1.c,which turns on eachLED in the matrix in sequence. With the LED matrix and driving circuit behaving asI expected,Ithen createdcMatdx 2.c in which a col-

0b100L001, 0b1001001, 0b0110110, 0b0000000, obo1,141,1,o, 0 b 1 00 0 0 0 1 , 0 b 1 00 0 0 0 1 , 0b0100010, 0b0000000, 0b1111111,

with

Next r,etter

//

nct

//

Einal

0b1000001. 0b1000001, 0b0111110, 0b00000001t

nain( )

{ PORTA = 0i PoRTc = 0b000001t CMCOIiIo = 7t a.NsEt = 0 t TRrSA = 0b101000t TRrSC = 0t Curletter

= 0t

// // ll // //

ALl Bits are Low stalt with Top lreft altrrL off compalatols off rrDc $rrn na5/RA3 Input8

//

start

wit'h

'A"

Fisure 613 5x7 LED matrix driven by a PICl6F684and 745126

S e c t i o n5 i x

Interfacing

Proj ects

for

the PICo llClJ

125

while(J.

== al

ll

Iroop tlorever

t (Dlay = 0r Dlay < 50r Dlay++) for for (i = 0r i < 4, i++) Character t // 20 mB to Diaplay * 5) + ilt j = Leteera[(CurlJett€r k = (j >> 2) e 0b010000, PORTC=j&0b1U111, PORITA=k+it for (n = 0t n < 259r n++)r / / 4 mE Delay // tof | Curlfette!

) |

= (Curletter

// elihw / / ED,d cMatrix

+ 1,, e.4,

ll

Increnent IJettser

It is interestingto seethat the characterdisplayis not substantiallylongeror more complexthan the first setof codethat movesthe lit LED acrossthe LED matrix.Most of the work wasspenttuning the 4 ms delayin the displayloop (the conceptusedwasto cycle through eachcharacter over 20 ms,requiring 50 repetitionsto displaythe characterfor 1 second).After mappingthe LED matrix pins and beforewiring the application,I spenta few momentsthinking how to most efficiently wire the application and wfiting out somecodeto figure out the wiring arrangementthat would keepthe codeto asfew instructionsaspossible.

2

E x F er im e ntlt 6 -L C D D i s p l a g

r. Prcr.5F68 4

tri

1 Two-line,

16-column

LCD

1 10k breadboard-mountable potentiometer , . 1

1 0.01 pF capacitor tYpe)

(any

Breadboa!d-mountable (E-Switch SPDT switch 8G1903 recomrnended) Needle-nose pliers

Breadboard-mountable momeotary On push button

B!eadboard

;'-':,:

Wiring

kit

Three-ceLI pack

AA battely

3 AA alka1i.ne

t.a

-;-i

:;i.a r,:,f

Creatingapplicationswith LCDS hasa reputationfor beingdifficulr.I would disagreewith this statement, noting that if you follow a simplesetof guidelinesyou really won't haveany troubles.The circuitpresentedin this applicationcan be built andprogrammedin aslittle as5 minutes.And, if you would like to enhance(or change)the output messageor add more functionality to the application,you will find it to be quite easy(asI will demonstratein the next experiment). In 123RoboticsEtcperiments for theEvil Genius,I includeda fairly comprehensive explanationof how to interfaceto Hitachi 44780controlledLCDs.I am not goingto repeatthat informationherebut will point you to my web site (www.myke.com) whereyou'll find informationregardinginterfacingto theseLCDs and

L26

batt eries

programmingthem.Along with thesetwo references, you'll find additionalreferenceson 44780-based LCDs. I shouldpoint out that 44780-based LCDS are text basedonly and havea 14- or 16-pininterface,andyou canprobablyfind somesurplusor old productsforjust a dollar or two. Graphic LCDs have a different interface and require a completely different interface. The circuit that I usedfor this experimentis shown in Figure6-14,and there are two thingsI want to bring to your attention.Most LCDs require4.5to 5.5volts, not the 3 volts I haveusedup to this point on breadboard circuits.To provide the LCD with the correct voltagelevel,I usedthree alkalineradio batteriesin a seriesclip to provide4.5volts.If rechargeable batteries are to be used(whichproduce1.2volts per cell,instead

- JE x p e r i m e n t s f o r l , e 3 P I C @l ' 1lC

the Evil

6enius

tlitachi 44780 Baaedl LcD This Ptoglaln rnitializes to in 4 Bit Moate anat then vrriues a sfurD1e atring nras useal to tir€ alelay values. it. The simulator can be founal

'.cD write Infomalion hltp: / /www. rnyk€. con

RC3:RCo - I . c D I / O D 7 : D 4 ( P i n s Pin RC4 I.cD E clocking RC5 LCD R/S PiN

at

1{:11)

rnyke prealko 04.11.08

-: I I

Figute6-lq

CONFIG(INEIO & WDTDIS & PITRTEN & I'ICLRDIS & IINPROTECT \ & UNPROTEC!! & BORDIS & IESODIS & FCIiIDIS) i

LCD circuit

int

j,

i,

k,

ni

Use clobal Debug

//

for

variables

Display <- usedt to organize // f23t567B91f23455 "i PIc Mcu const char TogMessage [l = rr "i = " Evil- Genius const char BolMessagel] +define

E

Rc4

*ilefine

Rs RC5

Define contlof

//

Declare a con8tant f o r 2 0 m s Delay

const

int

TwenEf.nr6 = 4250i

const consl

int int

Fivems = 300t TvroHundlrealus = 10t (int

r,cDwrite

iflt

tcDData,

the LCD Pins

//

Rsvalue)

{ PORTC

=

(',CDDaCa

>>

{)

& OxoE i

//

Fisure6-15 LCD breadboard RS = Rsvaluet E = 0t E - 1r

of the 1.5volts per cell of alkalinebatteries),you will haveto usefour in series. Normally whenI presentan LCD applicationfor the first time,I usethe full eight-bitinterface.Inthis case,becausethe PIC16F684only has 11pins with output capability,therewould be no pins left for interfacing.Therefore,Iusea four-bit interface.To reducethe requiredpin count to six,I alsotied the positiveactive read,negativeactivewrlte(RJW)low and don't poll the LCD.The six-birinterfaceusesall of PORTC,leaving PORIA free for interfacingto other devices. Whenyou look at the schematicin Figure6-14,you might be surprisedat someof the pin wiring choices.I wantedto makesurethat the circuit couldbe wired easilyand clearlyon the breadboard(seeFigure6-15). Secondly, I wantedto arange the bits so that the programcouldhandlethem easilywith a minimum of processing. #incluate - write clcD.c /* 4{780 LCD r/E

PORTC = IrCDData

& 0x0Ft

RS = Rsvaluet E = 1t E = 0,

S e c t i o nS i x

to

a 4 Bit

Toggle the Bits out

//

GeL Low 4 Bils Output

4

for

TJow 4

((0 == (LCDData & oxFc)) && (0 == RsvaLue) ) n = Eivemsi // Set Delay IntervaL else n = Tvollunalrealu s t if

(k = 0r k < nt

for )

//

k++)i

DeTay fo'.

//

clEractel

Enal LcDlsrite

nain( )

t PoRTc = 0, CMCONo = 7t aNSEr, = 0t TRISC = 0t

// // // //

Ei.tachi

Intenfacing

High

//

the / / aoggfe Bits Out

!or,t vrith Ev€rything Start B)tn otf Comparators Turn off iulc Alf of PORTC are Outputs

/ / a')iEi.aJ-i,ze LcD accortling j = tltenttzns, (i = 0r i < jr i++)r for a String

Gel Hish { Bits f,or OutsI)ul

Proj ects

for

to //

the

web Page

wait f,or IJCD to Power Up

t h e P I C @l { C U

L2'7

PORTC = 3, E

=

T;

E

=

U'

J = Fivemat f o r ( i = 0 r i < j t

i?. r:

qi; --},,: i"{

#-4

E = 1r E = 0t J - TwoHunalrealuBt f o r ( i = 0 r i < j , E =

r;

= ut

!

j = TrroHunalrealus; for (i = 0, i < jr

rt

start

//

Senal R€a€t. Cdunanal

IJcDwlile(0b0000U10,

//

Repeat

Reae!

Colnnanfl

LcDwrite(0b11000000,

cqmanal

(i = 0, Botuessage lil for LCDWrite (BotMe€sage Ii] ,

//

Rep€at Reset Third Tine

?urn On IJCD antl Enable Culsor

t= 0r i++)

//

Move Curaor !o th6 geconal ].ine

whil€(l

== 1)t

l= 0r i++)

//

Einished

i++), Inittalize Mode

i++)t /l

I.CD is { Bit !/t. 2 tJlne

LcDvlrit€(0b00000001, 0),

/ / Clear

I,cDwrite ( 0b00000110, 0),

/ / llove

]JCD

Curao! After Each Characle!

f!i

//

Erd

cr,cD

LCD 4 Bir

ut

j = TwoHurar€aluat for (i = 0r i < jr

0) t

//

i++) t

//

E =

0),

(i = 0t TopMessageli] for IrCDWril€ (TopMeEEage I i l ,

i++) t

(0b00101000, Ott IJCDWritse

.r-.9

Inilializalion

)

PORTC= 2, E =

//

LCD displaysin electronicapplicationsare useful from a number of perspectives;first they allow you to createverbose,usefulmessages either to yourself(as debugginginiormation) or to the user.Secondly,they add a level of commercializationto an aoDlicationthat givesthe appearance rhala lot morewoik hasgoneinto it than actuallyhas.Although requiring a bit more work to add to a microcontroller project than, saya few LEDs, LCDs can add a lot to your application,and I recommend that you considerthem wheneverit is possible.

j.=.*r

Experiment Q7-ProducingFlandsmNumbers

a :

.# ! ' ?

-"1

I

P I C 1 6 F 5 84

1 tvro-lj,ne,

I6-column

LCD

1 10k bleadboa!d-mountable potenti,ometer

3.,.{

0. 0l pF capacitor tYp€)

x :

Breadboard-mountable (E-Switch SPDf st{itch 8G1903 reconmended) B!eadboard-mountable momentary On push button

Needle-nose pLiers B!eadboard Wiring i,:

kit

fhree-cel1 pack

l'a ,.-1 . ,:'€

i.; ,i!!

i...-;

(any

AA alkaline

Peopleare usuallysurprisedto find out that producing random numbersin a computer systemis an incredibly hard thing to do. Probably one of the most creative methodsfor generatingrandomnumberswascreated by SiliconGraphics,Inc. engineerswho pointed a video cameraat a "Lava Lamp" and usedthe digitizedoutput asa randomnumber.Computersare poor random numbergeneratorssimplybecausethey are designed to work the samewav everv time. and for most com-

L28

AA battery batteries

puter applications, randomresultsare not a good thing. Although very few large(on the order of billions of bits) randomnumbersare requiredwithin microcontroller applications, you'll discoverthat thereare a numberof applicationswherea few bits of random datawould be useful.Computergamesare a common computerapplicationthat usesrandomnumbers,asare other applicationsthat interfaceto humansThe element of randomnesscanmake a gamemore interest-

l , P 3 P I C @l ' C l l - JE x p e r i m e n t s f o r

the Evil

Genius

ing or help keepan applicationfreshto the user.In this experiment,Iwill showyou how the usersthemselvescanbe usedto createthe randomnumbersfor an application. Thismight seemlike a paradox How cana user generaterandomnumbersfor an applicationthat apparentlybehavesrandomlyfor the user?The answer comesfrom the unexpectedtime the usertakesto respondto programoutput.By runningthe TMRO eight-bittimer at full speedand addinga debounced button on a pulled-upinput pin to the LCD display application,a computersystemthat generatesand displaysrandomnumberscanbe built very easily(see Figure6-16). In cRandom.c,I haveenabledthe PORIA pull-ups to allow me to wire to grounda simplemomentaryon switchasmy randominput device.When the user pushesthe button to producea new randomnumber, the cunent valueof TMR0 is read and convertedinto a decimalnumberto displayon the LCD. This techniqueis very simpleand,other than addingthe switch,doesn'trequireany extra hardware. High-endrandomizersproducetheir datafrom such

---Ti.:

I Figure 6-'fE

Randomcircuit

esotericsourcesasthe electricalnoiseinsidea diode. Granted,the high-endrandomizerscanproduceessentially limitlessstringsof randombits,but for most PIC the eight bits that are microcontrollerapplications, producedeverytime a userpressesa button are more than adequate.

l

. l

LED Displag Experimentt-.18-Ttno-Bit l . , i

I

,:. ' r,l

Prc12F6?5

1 74LS174 hex D ftlp I

fl,op

1N914 (1N4148) silicon diode

1 Two-line,

15-column

LCD

1 1k resistor 1 10k breadboard-mountable potent iometer 0.01 pF capacitor tlpe )

Needle-nose pliers B!eadboard Wiring

Three-ceLl

S e c t i o nS i x

Intenfacing

(anY

Breadboa!d-mountable (E-Switch SPD! switch EG1903 recor nended)

kit

A six-wire LCD interface is a great improvement over the full 11-wireoriginalinterface.It's still a lot of I/O pins,especiallyfor the lirnitednumberin the PIC16F684or the PICIZF675(whichalsocamewith the PICkitrM1 starterkit).What is neededis someway of convertinga serialsignal.A serialsignalwould be ideal,and a numberof serialLCD interfacesare on the

. . :

AA battery

market.Thesedeviceshavethreedrawbacks.One is their cost:Theseinterfacescancostanywherefrom $20 to $100.Secondly, they do not work at the speedof the microcontroller.Lastly,neitherthe PIC16F684nor the serialinterface. PICIZF675havean asynchronous Theseissuesdo not eliminatethe useof a serialLCD interface;theysimplymakeits usemore problematic.

Projects

f o n t h e P I C @l l C U

129

A better solutionis the two-wiresynchJonous serial interfaceshownin Figure6-17.The shift register allowsthe minimal condition six-wireintedaceto be usedwith the LCD module.This circuit combinesthe mostsignificantbit (which shouldonly be set whenall the other bits are loaded)and the data line to form the E clock.This methodis obviouslyquite a bit slower than the methoddemonstratedin the previousexperiment,but for most applications, the speedis not a major concern.

-_1 ' ---l J

!

l.-{

T

I

._;

.-+

The actual operating waveforms are shown in Figure 6-18.First the contentsof the shift registerare clearedby shiftingin six zerosand a high bit. Next the RS bit followed by the four databits for the nibble are passedto the 74LS174,which is wired asa shift register.When the data is valid,the data line is strobedhigh and low to load and storethe new characteror instruction into the LCD. When I createdthe codefor this experiment'scircuit,I usedthe codefrom the previous experimentasa base. For this experiment(seeFigure6-19),I usedthe PIC12F675that camewith the PICkit 1 starterkit.You couldusea PIC16F684, but I wantedto usethe PIC72F675as anLCD enabledsensorcontrollerin a (much)later experiment.By creatingthis experiment usingthe PIC12F675,Icreatedthe basethat I would needfor the later sensorexperiments:APIC16F684 (or any other PIC MCU) couldbe substitutedin the

-Ti]-TB-T

--f

Dab

l];-l

tr l

61651ffi

;,0. a -,e.- a"

2q-,o. 36-:c.

F---]-;-EE-fii-r"r-T]JT*-TilitTu-iif-T.iiTfil1;iir--T-$-E?;-

-roo-2oo-la"

4e-iao 5Q-

5ro -!oo - rae-,0

6A_

610 - 5oo- !€o- :0.-,oo-'oc

E 4

'E Active

(60. Data)

Figure 5lB

Two-wirewaveform

Figure 6-fg

Two-wirecircuit

!.!"9

: ; i i

{..

t

circuit. You would simply have to changethe Clk and the Data #definestatementsin the cLCD2Wire.c application with the pins and devicethat you are using, and then make surethe specialfunctionperipheral analogpin controlswill allow thesetwo pins to execute asdigital I/O. When I wired my prototype circuit, I useda long breadboardto allow a comfortableamountof sDace for the 74LSl74shj[tregister. I alsospentsomerime trying to keepthe wiresasneat aspossiblebecauseI want to use this circuit in later experiments.If possible, put this breadboard circuit asideuntil you work up to the sensorexperiments. which usethis circuit asa base.

Figure 6-f7

Two-wireblock diagram

130

l , e 3 P I C @l l C U E x p e ri me n t s f o r

{li

e'i !"*

t-t{ ,i-?

the Evi I

Genius

Experimentt.l9-5tuitch Matrix KegpadMapping

Needle-nose

pliers

B!eadboard Wiring

I

P I C 1 6 F 6 84

0.01 pF capacitols

1 74LS174 hex D flip I

I

16-column

I

diode

LCD

10k resistor

SIP

10k breadboard-mountable t iomet e !

A switchmatrix keypadcan be a very usefultool for enteringarbitrarydatainto an applicationor for applicationcontrol.It canbe so useful,in fact,that you will considerpayingthe often-exorbitantfee for a single keypad.New,they costanywherefrom $25to $100for a 4x4 switchmatrix keypad.With a bit of hunting,you canprobablyfind useablesurplusswitchmatrix keypadsfor a few dollars.But, asthey don't comewith a you will haveto figure out how they are datasheet, wired on your own.Thetaskof r??rpping, or decoding, the keypadis surprisinglyeasyand can often be done usingthe samehardwareasyou will usefor the final applicationthat usesthe keypad.

Figure 6-20 Keypadmappingcircuit consistingot' a keypadconnectedto a PIC16F684driving an LCD

S e c t i o n5 i x

(any type)

16-button switch matrix keypad or nine-pin bleadwith an eightboard interface Breadboard-rnountable SPDT switch (E-Switch EG1903 recoftnended)

1k lesistor

1 10-pin, I

flop

1N914 (1N4148) silicon

1 Two-1ine,

kit

1 fhree-cel1 poten-

3 AA alkaLine

/dA battely

pack

batteries

The keypadI choseto map for this experimentis the l6-pin keypad,shownin Figure6-20,and hasnine pins on the backsidethat canbe presseddirectlyinto a breadboard(whichis why I choseit). The circuit used to map the keypadis basedon the two-wireLCD interfaceshownearlierin this section.but insteadof the PIC12F675,Iuseda PIC16F684to take advantage of its 1l I/O pins.Thecircuit usedin this application simplywireseachpin to a pulled-upkeypadpin with the two leftoverpins connectedto a two-wireLCD interface(seeFigure6-21).

Figure 6-el

I n t e n f a c i n g P n oj e c t s

Keypaddecode

f o r t h e P I C @l l C U

131

The mapping software (cKeyDcode 2.c listed after t h i sp a r a g r a p hi)s q u i t e s i m p l e I. r c o n t i n u l l l vm a k e 5 one pin a low output and scansthe remaining pins to seeif any are low (a key is pressed).Ifan input goes low,it is assumedto be a row, with the column b"eing the output pin.These two pins are displayed on the circuit's LCD.When the key is lifted,the LCD values are cleared and the program resumes its scanning.I have not debounced the inputs, as multiple keypresses would be invisible to the user and not affect the oDeration of the application.I have not included the listing ior cKeyDcode 1.c,as it is a copy oi;a;-rwi,."".-* modified for the PIC16F684 and created as a base for cKeyDcode 2.c. #inclutte cK€yDcoale 2.c /*

- Ket pail

t ._- . Data = 0t for (i = 0' i < 6i i++) {

,

coat€ is

else Data lcDout

Decoale util.ity

aA2 RCo RC1 RCz RC3 RC4 RCs

-

Pin Pin Pin Pi.n Pin Pin Pin

7 6 5 4 3 2 1

Kelrpaal Ket paal Ketrpaal Kepaal Ketrpaal Ketzpaal Kq4)aal

of of, of of, of, of of

Data

RA{

L32

r,

lcDData,

i'It

Rsva]"ue) / / send

Bvte

to

],cD

li

Nvbbl€shi ft ( ( r,CDData >> {) & 0x0F, RsvaLue) t ( r'CDData & 0x0F' Rsvalue) t NvbbJ eshift // Shift out Bvte

& rEsoDrs

//

Twenlyms

//

the IJCD Serial PinE

Declare a Constant fo! ms Delav-

20

!cDou!,

j.nr

Rs)

//

shift out Nybble

i,

< i;

j++)t

Delav

//

f,or

charactel

j;

PoRTA = 0t CMCONo = ?i ANSEI. = 0; TRISA4 = 0, TRTSAs = 0t //

Fivems = 300, = 10r TwoHundreilus (inr

j

rnain ( )

int

= f25O,

= 0t

Enat lcDwrite

//

]

& FcltDrs),

orz34567ago!2345 = nRc'xr: , ' C o hlnn: "t = Defi'Je control

(j

for

& pwRTEN & Mcr,RDrs &

TopMessage [] Botl4essaEe []

*alefilre

Nybbleshifr

End Nybbreshift

//

anc

& BoRDrs

AA5

in! int

Clock the Nybble int the LcD

NOPO, Data = 0,

LCDW?ite (int |

& wDTDrs

Clk

const const

//

((0 == (rJCDData & oxFC)) && (0 == Rsvalue) ) i = Fiv€ms, // Set Detay Interval else a = TwoHuftl-ealst

#alefine

int

//

shift up the Nett Bit Clock uhe Bi! iltto the s/R

j.f

-coNFrc(rNTro I'NPROTECT \ & uNpRorEcr

eonst

//

NoP()t Data = 1r

-t

char char

<< 1t

ait

0t rof

-ctk.= // )

myk€ pretlko 04.12.05

/| const const

= 0t = LcDout

C1k = lt

] Ket|I)aal

out the

Hiqhegt

based on cKeyDcode 1.c

9 of

c1k = 0, // 1.or

if (0 r= (r,cDou! & (1 << s) ) ) Data = 1t // shift

R:A4 _ Data RA5 - clock AA0 - Pin

// irusr rossle rh€ clock

IJcDout= rcDout | (1 << 5) | {(Rs & 1) * (1 << 4))t ror (i = 0' i < 5' i++) // shirt Data c'ut

This ProEram constantl.y Ecarrs the Ketrpaal wireal to RAO-RA2 andl Rco-Rcs ba makingr one pin a tow (trColunnn) anal lhen scanning the pulleat output (trRowr) to 6ee if any are Low pins up r€naining anal lhen alisplays the trCathoale" and nltnodle" oa an attacheal 2 Wire LcD Interfaee. This

clk = 1,

// clear the shift R€Eiseer

// // // //

starl with Evervthing ConEarator Off rurn off ADC Enable r/O Pins

IniEialize LCD accoraling j = Tweatlansi (i = 0r i < jr i++), for

rhe

l , a l P I C @l l C U E x p e r i m e n t s f o r

the EviI

to //

th€

Web Page

Wait for r,CD ro Po\rer I'I)

Genius

Low

( 3,

lBrbblesbifl

j = Fiv€ost for (i = 0r i

0),

//

< jr

// i++)t

trl

gtart

InltlallzaEion Proc€aa Corutantl Seltl Res6t

for (j = 1r j swilch(j )

<= 9,

X

j++)

b

t 0)t Nybbleshift(3, j = T$oHuadlr€ilust fo! (i = 0, i < j; ( 3,

Nybbl€sbift

ReDeat

//

R6aet

case 1l if, ((i

Cormaatl

0),

//

J = Tarofluntllealua i for (i = 0r i < j;

i++);

rDabbleshifr (2, 0)r

//

R€peat R€set rhirit Tinre

I.cD { Bit

raitialize uod€

breahi caa6 2: tf ((I

//

LcD is { Bit 2 Lin€

LcDwrite ( 0b0000000L, Ol,

//

C1€ar LCD

I,cDwlite ( 0b000 001LO, Or,

ll

llov€ Cursor After

r/F,

cas6 3: ((i if {

rurrr On LCD anal Eaable curaoi

ll

(i = 0t lloDll€asag€ [ ll for l= LcDlltite(TogMeEsagetil ' 1) t ( 0b110000 OO, Ol?

(i = 0r BotMeesag€lil for LCDwrit€ (BotM€ssage til , rcbile(J.

== a)

ll

(i

= 1t i

<= 9t

0,

l++)

llove Culsor Seconal IJl,ne

ll

t1) t

0r

to

the

(i )

i++)

Einiah€al Ket'9eal

-

o

F

af

PuII Fiail

ll

Rolr

.t\

Colur|a

tA v I I

l= 51 69 19 == Rc3))

Writ€ Row

a

llrite

{

Co1trl[n

r= j)

Scan the

Down Each 'Colu![ns"

Pi!

to

0,

0t

0t

0,

0,

f-,

cr

ff

o

r

&& (0 == Rc2))

tCDryrite(0b10000101, 0), LcDwrite(j + r0,, 1)r // LCDwrite ( 0b11001000, 0) t r0', 1); lcDt{rite ( i + // wbile (0 == RC2)t | // fi

{ caa€ 1: TRISC5 = b!€akt caae 2: IiRISC{ breakt cage 3l TRISC3 = breakt caaa {: liRISC2 = br€akt caae 5: ERISC1 r breaki case 5: TRISCo = breakt caae 7t TRISA2 = br6akt caae 8: TRISA1 = bleakt caso 9: TRISTAo = br€akt // hctilta )

colurn

t

i++) //

I

breakt caae 4: if, ((i

{ avLtcb

vrrire

Ft F. =1

&& (0 == Rc4))

LCDwrit€(0b10000101, 0), ( j + r0,, 1)r IJCDDrrit€ // I.cDwrite ( 0b11001000' 0) t lcDvEite (i + r0', 1)r // while (0 -- RC3)t

t for

Rolt

lcDwrtte ( 0b10000101, 0) t r,cDwrlte(J + r0', 1)r // wtile LcDwrite ( 0b11001000, 0) t + t0,, 1)r lcDvEite(i // write while (O == RC{)t , ll fL breakt

Each Cbaracler Ot,

t= j)

writ€

{

( 0b00101oOO,olt lI,CD0EIfite

LCDWrit€

o

&& (0 == Rcs))

I,cDtflite ( 0b1000 0101, o); + t0', 1), LcDwribe(j // lcDwrltse ( 0b110 0100 0, o)t 1), lcDwrl.tse (i + r0,, // lthLl€ (0 == RCs),

cdurenal

j = TaroHuadr€auEt fo! (t = O, I < J, i++),

T,CDw:.it€ ( 0b0 0001L10,

l= j)

{

i++)t

Wril6 Rolt wrlt€

coluan

b!€akt

caae 5: tf ((i != j) && (0 == Rc1)) t LCDwrIt€{0b10000101, 0), LcDwrLt€(j + r0', 1)r // vlrile Row Lcryrrtr€ ( 0b11001000. 0) t LCDIYIit€( j. + r0,, 1)r // Wrile Colu$! while (0 -- Rc1) t ll ti, breakt case 6! it ((i l= j) && (0 == Rco)) t LcDvfritse ( Ob10000101, 0) t lcDwrile (j + r0,, 1)r // Wtite Rort LCDwrit€(0b11001000, 0); IJCDg{rile ( i + r0,, 1)r // Wtile Coluffi vhile (0 -- Rco)t

9' cf r-l l-r.

x

X o r<

rd 0, g

0t

breakt caaa 7l lf ((i

0,

!= j)

{ LcDwrite(0b10000101, 0) t + r0', 1), lcDyElto(j // writse Row LcDwrile(0b11001000, 0), LCDWtile(i + r0,, 1), // Wrlt6 CoIutB while (0 == RA2)t I // EL br€aki

0t

0t

S e c t i o n5 i x

Interf acing

Projects

f o n t h e P I C @l l C U

3 s

p,

&& (0 == Rr2))

1.33

6

F. Lt

uq

((i

if

t

&a (0 == RAl))

!= i)

r,eDwrile(0b10000101. 0) t

+ \O', L)i LcDwrite(j // rcDwriLe (0b11001000. 0) t + \O', r), lcDwrite(i l/ $rhi1e (0 == RA1) t // fI I break; ((i

if

!= j)

write

Column

&& (0 == RAo))

t LcDwrite (0b10000101, 0) t + .0,, 1)r r,cDwfite(j // wrire (0b11001000, 0) t Lcrfirite LCDWrite(i + \0,, 1)r / / w r i t € colurn while (0 == RAo); // fr l bleakt // hctiws ) lcDwrite ( 0b10000101, 0) t '. 1), I,cDwrite(' // Clear Row lcDwrile (0b11001000, 0) t I,cDwrite ( r \, 1), // C1€ar Column TRIsc

= 0b111111,

//

Restore Everything lligh for Next

TRISA = 0b001111t j // rof // elihw ) / / E'ld cKeyDcoale 2 ,

After runningthe program,I createda tablethat mapsthe rows and columnsfor eachof the keypad's pins (seeTable6-1).The numbersafter "Row" and "Column" indicatethe keypadpin numbers,not some definitionof row and column. As I saidpreviously,I useda keypadwith a nine-pin interface-pin 9 is neverlistedasa row or column. Testingthe keypadwith a digiralmultimeter(DMM),I discoveredthat pin 9 is an additionalrow pin that gets pulled low whenthe "2nd" key is pressed. This feature allows"znd" to be pressedalongwith the numberkeys to indicatea hexadecimalnumber.I will usethis keypad (and the informationprovidedhere) aspart of a sensorcontrol module,and,insteadof usingpin 9, I havecomeup with a methodof enleringin hexadecimal valuesby recordingthat"2nd" waspressed.

Table 6-1 Sample KeUpadDecodingN4atrixlNumbers "FIDLU" "Column" beside and are the kegFad'sFin numbersl EolumnI Eolumn2

Column3

Columntl

Row 8

"2nd"

DownArrow

Up Arrow

ENTER

Row 7

9

6

3

HELP

Row 6

u '7

5

Row 5

r5{

4

2 1

0 CLEAR

When I seean interestingkeypador switchmatrix keyboard(often built for old homecomputersystems), the easeby which it canbe decodedis what leadsme to finally chooseit. In this experiment,Ishowedyou how to map a keypad;the processof mappinga keyboard is exactlythe same-it simplyrequiresmore I/O pins.Although you might be temptedto map the keypad usinga DMM, why don't you try out this application with somethinglike a PIC16F877A?This chip (supportedby the PiCC LiterMcompiler,so the ckeyDcode2.capplicationcanbe usedasa base)provides up to 33 I/O pins,which meansthat you will be ableto map keyboardswith up to 31 I/O pins with two pins Ieft over for the two-wireLCD interface.

For EonEideration Although it is goingbeyondthe scopeof this book,I did want to presentyou with the conceptof interrupts and how they canperform somepretty amazingtricks. Interruptsare specialsoftwaresubroutinesthat executewhena hardwareevent(e.g.,a timer overflowing, a pin changingstate,databeingreceived,or a conversion operationbeingcompleted)takesplace.These subroutinesare usuallywdtten to be independentof the mainlinecode,with flag bits or data variablespassing the resultsto the mainlinecode.Interruptscan reduceyour applicationcoderequirementsby up to 80 percentand variablerequirementsby 30 percentor more.It canbe difficult structuringan applicationto useinterruptsand makingsurethey do not negatively affectthe operationof the applicatlon. The executionflow of the interrupt subroutine,or handler,is shownin Figure6-22and stafiswith a hardware eventrequestinga responsefrom the intenupt handler.Whenthe processorrespondsto the request, the curent programcounteris savedand the stateflip flopsin the processorare set to indicatethat an interrupt is beinghandled.Executioncontrol is then passed to the subroutinehandler,and the registersrequired for all programexecution(calledthe contextregisters) are savedbeforethe registersare changedfor the interrupt handler.Theinterrupt handleritself should executeasquickly aspossibleto avoidinterruptingthe flow and resDonsiveness of the mainlineand to make sureit isn't executingwhen anotherinterrupt request is comingin, whichcould resultin the secondinteffupt beingmissed. I mustemphasizethat interruptsare requests;the applicationcodecanchooseto not respondto them immediatelyor evensimplyto handlethem aspart of the mainlinecode.Thisrangeof variabilitymustbe in the applicationto make sureinteraccommodated

l , e 3 P f C @l l C U E x o e r i m e n t s f o r

the EviI

6enius

rupt requestsare not lost or handledin the wrong order,which canhappenquite easily.Oncethe interrupt handlerhasfinishedexecuting,the contextregistersare restoredto their pre-interruptvalues,the interrupt requesthardwareis reset,and the execution retums to the mainline,asif nothing had happened. Despitethesewarnings,interupts can be addedto an applicationquite easilyasshownin cPKLEDInt.c. This applicationis anotherof the PICkit 1 starterkit LED sequenceprogramsin whichTMR1 is allowedto run at clock speed(4 MHz) with a divide-by-8 prescaler.Every time TMRl overflows,which happens after a little over a half second,an interrupt requestis madeand respondedto by turning off the current L E D a n dt u r n i n go n t h en e x to n ei n s e q u e n c e #incl"ual€ - Roll cPKLEDht.c /* TriIRl Int This Program rrilL LED€ built into th€ PICkit

ro11

i n t k = 0 t

consr char TRrsvalue[8]

voial |

TMR1IF = 0,

//

Reset rlne! Requ€st

pORrA = IrEDValue lkt r

//

Point I,ED

//

hcrement range of

(k

k= €ach

through

When the

(void) / / Respollal lo Inte!rupc

to

of

the

+ 1)

Tiner

1

InternPt

lhe

Culrent

[k] t

LEDS Using

PICkit

% 8,

k q'ithin 0-7

8 )

PCB.

tlnr].iat

interrupt

TRISA = TRISValue Through

= t0b010000, 0b100000, 0b010000,0b000100, 0b1ooooo,obooo1oo. 0 b 0 0 0 1 0 0 , 0 b 0 0 0 0 1 0 t) = t0b001111, 0b001111, 0b101011,0b1010!.1' 0b011011,0b011011. 0 b 1 1 1 0 0 1 . 0 b 1 1 1 0 0 1 t)

const char lEDvalue[8]

T1 intelrupt

tn.rlint

//

ia nain( )

The r,ED valu€s rrED DO D1 D2 D3 D4 D5 D5 D7

A.noale RA4 RA5 nA4 RA2 RA5 RA2 AA2 RA1

t

are:

PORTA

cathoale AA5 AJA{ Ri[2 R'[4 RA2 R]A5 RA]. RA2

PEIE = 1r = 1r GIE TMRLIE = 1; while(]. l

& CONFIG(INTIO & WDTDIS & PWRTEN & IICLRDIS TINPRC/IECT \ & UNPROTECT & BORDXS & IESODIS & EC!4DIS ) t

Handl e r Executron Mainl ine R el u r n

JumP

H a n dL er

Mainline Coaie Execut-ion

M a i n L : Ln e Code Execution

uaraware ftty v I nterrupt

Figure E-aa

Ot

rurn

off

ANSEIJ = 0t TMB1IJ=TMRlB=0t TICON = 0b00110101t

myk€ plealko 04.09.10

Execut ron

=

cucoNo = 7t //

Peq,JesL

//

// // //

Enable Enable Enable

== 1)t

Compalators ADC // Turn off 1 // Reset Tiner // Enable Tr,lR1 Interrupcs Perigheral' Gl.obal Interrupta 1 Interrupts Tiner //

LooP Fotever

E'ld. CPKTJEDInI

The main interrupt operationcontrol is the INTCON register'sglobql interruPtenable(GIE) bit, which,whenset,allowsinterrupt requestsfrom the different hardwaresourcesin the PIC MCU. For every "lE" interrupt source,thereis a registerthat endsin (for interruptenable).And when this bit is set,an interrupt will be requestedand the interrupt subroutinewill be called.In the PIC MCU, therecan only haveone interrupt subroutine,and in the subroutine,the differ(IF) bits are polled to seethe enl interruptrequeslrflag sourceof the interrupt.In cPKLEDInt.c,thereis only one interrupt enablebit set (TMRIIE for TMR1 overflow interupt requests),so I don't bother polling the register. The PICC Lite compilermakesworking with interit placesthe interrupt rupts quite a nice experience; subroutinehandlercodeat the correctaddresswithin t h eP I CM C U a n dh a n d l etsh ec o n l e xrte g i s t esr .a \ i n g and restoringfor you.When you are readyto start

Interruptflow

S e c t i o n5 i x

Interfacing

Pnojects for

t h e P I C @l l C U

135

trying out interruptsin your own application,I highly recommendusingthe PICC Lite compilerbefore assemblylanguage. Comparing the application hex file sizeof cPKLED.cand cPKLEDInt.c,you'll seethat cPKLED.cis 130instructionsand uses10file register bytes,while cPKLEDInt.c is 102instructions(a 20 percentreductionin size)and usesnine file registerbytes. What is really amazingabout this application is that the mainline,consistingof the single"while (1 :: 1);" statementnow,could be usedfor anothertaskbecause the TMR1 interrupt driven subroutine is completely independentof the mainlinecode.And becauseit

requires approximately 38 instruction cyclesout of every574,288,only 0.0075percentof the available instructioncyclesare lost.Youcan havea complete application running while the LEDs are active and not evennoticea drop in performance. This type of improvementin programparametersis pretty typical when interrupts are added to an application. When you are comfortablewith programmingthe PIC MCU in C and assembler, you will be very readyto start to implement interruptsin your own projects.You'lllearn how they canmake a programmore efficientand (ironically) easierto write becausecomplexhardwareinterfacescanbe independentof the mainlinecode.

-J

1 " ttl

1-;

i,f

136

l , e l P I C @l l C U E x p e r i m e n t s f o r

the Evil

Genius

Section

Seven

Samplef Microcontroller Hpplication5

A certainperceptionis held by many hobbyiststhat practicalmicrocontrollerapplicationshavelobe coded in assembler. The reasonfor this feelingis basedon the expectedsuperiorityof assemblylanguageapplications in termsof speedandsize.Theseexpectationsasto the superiorityof assemblylanguagereally don't hold any water;modem compilers,suchasPICC LiterMcompiler,producemachinecodethat is often just asefficient asthat usingassemblylanguagefor a given operationor statement.And no reasoncan be givento use assemblylanguageexcept in situations where custom interfacesare requiredandnot availablein prewrittenlibraries.Being ableto write applicationsin C is prirnarily dependanton the ability of the programmer to designapplicationcodethat is properlyorganized. For somereason,properlyorganizingthe microcontroller application seemsto be quite difficult, when in fact they usuallyonly needto usethe following temDlate: lrai.n ( )

There is no chancethat an inDut statewill be missed.

As a rule of thumb,you can assumethat "essentially zero time" meanslessthan 5 percentof the next loop delay.Any longer than this (especiallyif it is variable), then you will find that the application will respond erraticallyand certainlynot the way you expect. If the application'sinputsare asynchronous and thereis a chancethat somethingwill be missed,then you will haveto modify the applicationorganizationto poll the inputswhile the next loop delayis executing: nain( )

// //

//

variable/Peripheral Initialization (riner) (lf Delay Inilializatsion !rhi1€(l

== Lt

//

Int€rface

(rin€r) D€Iay oDelatiod

//

) //

I

// elihw wrd sampLe

bef,ore

fequireal)

Perf,ot

Interface

Input |

MaiD Loop

)

Nexts Loop/Interface

c Baseal ADplication

Therereallyisn't much to this type of application, althoughI shouldpoint out two very important assumptions: .

requir€d) Main

Loop

(i

Nex! Delay

IJoop

Outsput O9elation

= 0r i < Dlayr i++)

//

{ //

operat.iorl lhe

//

Aslmchlonoua

{

I

Petfotfr

== 1)

while(l

for

t //

Microcontlo1l€r InI)u! ApDLicalion coate organization

valiabLe/Pelipheral InitiaLization (Tiiner) (if Delay Initialization

{ // //

//

t

//

BaBic Microconlloll€r Aflplication Coale Orgaaization

//

.

The output responseto a given set of inputs (or internal statevalues)takesessentiallyzero time -the outputsare basedon a calculationof the lnputs.

ll

Poll/Proceaaing // tof

// elihw ErLd. sarE)le

C Basefl

Application

This organizationof the applicationcodeallows asynchronous inputsto be recognizedwithout affecting the output timing.The reasonfor maintainingthe output delayis to allow any output interfacecircuitry to completetheir operationand any devicesconnected to them to acceptthe completeoutput from the microcontrollerand respondappropriately. For proper operation,I recommendusinga timer insteadof a for loop asI haveshownpreviously,and asthe input is polled, the timer valueshouldalsobe polled. The two code samplesshown here should not be surprising;I have been using them for many of the experiments'codeandwill usethem asa basefor the applicationscontainedin this section.In mostpractical applications, a greatnumberof fuad timeexecution

137

cyclesexistthat are not requiredfor applicationexecution.And the codesamplespresentedhere take advantage of this characteristicby organizing the input and output operationsto bestimplementthe application. By correctly organizing your applications execution, you will havea simplebasethat can be easilymodified into providingthe requiredfunctions.Most importantly,thesesampleapplicationscanbe written in either C or assemblerwith equal execution efficiency.

:*'t

You probably have noticed that I have not included a list of partsand toolsfor the experimentsin this section.This is deliberate,aseachexperimentis unique and independentof the othersin the section.I have included the list of parts and tools required for each erperiment, however,so you can build them on your own,

Experiment50-Pumpkin LEDBiEplag

;13 1

Prc16F684

1 1A-pin

socket

Hi9h-intensity

orange

0.01 pF capacito! tYpe)

b.a{ t*t

I

1,20V8-pin

(any

SIP

1 t DMM Needle-nose pliets Li

Soldering

*"

Prototyping text) Thfee-cell pack

irod

PCB ( s e e AAA b a t t e r y

AAA battelies

Solde r

*,: ii

I

l!

,

. !-,lr ;.-! iii

:-: !'! t ,l',.

4,it

irl:

I am breakingnew groundin this book.In all my previ ousbooks,I showhow to take advantageof linearfeedback shijt registers(LFSRS) to create a seemingly randomdisplayfor the holidays.In this book, I am "cangoingto useLFSRSto createa random-seeming dle" (seeFigure7-1) to put insidepumpkinsat Halloween.Theprojectideawastaken from Mark McCuller's "Pumpkin Light LED" project presentedin October2004's,eslgrzNewsand usesresistor-and capacitor-basedreflex oscillators to flash LEDs on and ofi I felt that the original would be quite complex to assembleand a PIC9 MCU application would allow me to decreasesignificantlythe numberof parts required(andthe work requiredto assernble it). I daresaymy versionis somewhatcheaperto build as well.Despitethe project'ssimplicity,it actuallyworks quite well andwon't burn and dry up the insideof your pumpkinsthe way a regularcandledoes. The Purnpkin circuit usesa 4.5V power supply (providedby threeAA batteries)that servesasthe basefor a small,cut-downprototypingPCB to which a switch,a

138

PIC16F684,a 0.01p,Fcapacitor,a 120OSIP resistor, and the six high-intensityorangeLEDs are soldered.

Fisure 7l Pumpkin artificial cantlle on a three-cell AA batterypqck

l , e 3 P I C @l l C u E x p e r i m e n t s f o r

the Evil

6enius

This cilcuit (seeFigure7-2) shouldnot be a surpriseto you,and is very similarto the previousexperimentsin this book. I wasableto soldertogetherthe cilcuit neatlyon a cut-downprototypingPCB.To further simplify the assemblywork,I usedan eight-pin,l200 single-inlinepackage(SIP)resistor,which containsseven resistors,eachconnectedto a commonpoint, To mimic the flickeringcandle,I wantedthe LEDs to turn on and off seeminglyrandomly,for random periodsof time (rangingfrom about one-tenthof a secondto one or two seconds).The mostobviousway of implementingthis is by an LFSR, and I decidedon usinga six-bitLFSR for the six LEDs on PORTC of the PIC16F684and a four-bit LFSR to specifythe lengthof time the LEDs would be in a specificstate.I expectedthe codeto be very simpleand similarto someof the earlierexperiments. However,before blindly writing the LFSR codeand attemptingto debugit in the applicationcircuit,I decidedI would simulateit first. The LFSRsfor this applicationeachhavea single tap,which is XORed with the mostsignificantbit and fed into the input of the first bit of the shift register.To test and demonstratetheir operation,I createdthe applicationCLFSR.c: *include cLFSR.c - Test /*

LFSR Taps

Thi6 plogfaln Te€ts 6 antl 4 bit L!'SR Ta!,6 to sure they Perform a ( (2 ** n) - 1) Maxinlllln Numb€! of timeE

nak€

!=

1)

t =

fourBitTrFSR

fourBilcount I

(fourBitlrFsR << 1) & 0x0F) + ( fourBitIJEsR >> 3) ^ (fourBitIJEsR >> 2) & 1))t = fourBitcount+ 1r // Keep Track of, slate #

/ / eLilrw

sixBitIJFSR sixBitcount

= =

// //

1t 1t

start at 1 Keep Track of

(sixBitlFsR ( sirrBitLFSR (sixBitlFsR ( sirraitlFsR t= 1)

sixBitLEsR

while

=

<< 1) >> 5) >> 4)

fourBitlFsR, fourBitcount,

sixBitlEsR

t

fourBill,FsR

= ( (fourBittFsR ( (fourBitlEsR ( (fourBitIJFsR

// //

+

& 1))t

sixBitcount l

//

& 0x3F) ^

+

& 1))t ll Ke6D Ttae]f of State #

eti'}r'''

//

while(1 )

= ( (sixBitLFSR << 1) ( (sitrBitlFsR >> 5) ( (sitrBitLFSR >> 4) = BixBilcounE+ a,

== 1) t

End CLFSR

The two countvaiables are usedto determinehow manyiterationsof the LFSR would executebeforethe valuereturnedto 1, at which time it would start all over again.When the LFSR tapsare properly placed, thereshouldbe 2'' - 1 iterations(15 for the four-bit LFSR and 63 for the six-bitLFSR).Amazingly enough,the two taps(thoseat the shift register's secondto lastbit) producedperfectresults,and they wereintegratedinto the cPumpkin.capplicationcode:

Haralware Notea: PrC16F684 Running at RCs:RCo - 6 ]JEDS

nain ( )

= 1, = ft

& 0x3F) ^

#

IJED6 on PORTC

This Prograltr will run cofltifluously tufiing on ],EDs for varying Lengtlrs of time to simulate a candle in a Pumpkin. Six Y611ovr anal Orartg€ High ploject. Intensily LEDa shoulal be useal with this

sixBitLFSR, sixBilcountt

fourBitr,EsR f,oulBilcount

Stale

{

#include - Ranalomly lJight cPumpkin.c /i

myke Dreatko 04. !L. r7

int int

( fourBitIJESR

while

start at 1 Kee r, Track of

Slate

<< 1) & 0x0F) >> 3) ^ >> 2) & 1))t

*

4 MEz

iryke Drealko 04. !L. r7

+ CONFIG(INIIO & I{DTDIS & PWRTEN & !,ICLRDIS & UNPROTECT \ & IJNPROTECT & BORDIS & IESODIS & F C M D I S ) ,

int int

i, j, k; fourBiUIFSR.

sirrBitLFSRt

main( )

t fourBitLFSR si.xBitLFSR

= 1, = 1t

CIIICONo = 7 t

Figure 7-2

// //

//

$)rn

Starl Starl

off

at. 1 at' 1

coinpalators

Pumpkin circuit

S e c t i o n5 e v e n S a m pI e C l 1i c r o c o n t r o l l e r

Applications

139

.lll\IsEr, = 0, IRISC = 0t lrhile(l

== L\

//

Tuln

off

aDc

//

IJoop Foreve!

t (k = 0r

f,or

h < fourBitsLEgR,

k++)

//

Delay 0.18 x 4 BiE IJFSR

(1. = 0 , i < 2 5 5 r i + + ) fo! (j = o t j < 2 4 , j + + r , for PORTC = sirrBiLLFSR

| f,ourBitrFsRt

I / \t€.:ri.llize + o f IrEDs on

t&l -

foutBitLFSR

airiBitLFSR

Ft

=

( (foulBitLFSR ( ( foulBitLFSR ( (foulBitlFsR ( ai*BitLFSR ( Ei*BitLFSR ( air{Bilr,FsR

<< 1) 0x0F) >> 3) >> 2) & 1 ) ) , << 1 ) & 0x3r) >> >> 4 ) & 1 ) ) t

+

The code is quite simple and straightforward except for two placesI would like to bring to your attention. The first is in the delay loop: I changedthe end values in a 500ms delayso that it was100ms,and then I addedanotherfor statementto multiply the delayby the value of the four-bit LFSR. Similarly, rather than just passthe six-bitLFSR to PORTC,I decidedto OR the two LFSRStogetherto get the maximumnumber of LEDs on at any giventime. The application works quite well and for a surprisingly long time. I must caution you againsttrying to stare into the high-intensity orange LEDs. They are bright enoughto giveyou a headacheand produce spotsbefore your eyes.

+

&4 //

End cPurekin

ni

Experiment 5l - Reaction-TimeTesIer

f-d

ri

t!

1

Prc16F684

I

l4-pin

I

1o-LED bargraph

1

10 /rF electrolytic capacito!

I

0. 01 /rF capacitot tYpe )

as,

socket display

(any

10k !es istols

t :

1 0 10 0C, resistors

DMM NeedIe-nose Solderj,ng

iron

Solder

I l.'l

Wire-wrap

I

Prototyping' text)

1

Two-ceII pack

2

AAA batteries

wire

Weldbond adhesive

,."a.

SPST switches

pliers

PCB (see

AAA battery

'-'r ,i? 1"3 " r I

fi-! f;t i{{

t\

A gimmickthat becamequite popularwhen I cameof ddnking agewasthe reaction-time,or sobrietytester, that consistedof a simplecircuit that would run a seriesof LEDs until a button waspressed.The reaction time beingtestedwasthat of an individualwho had beendrinking,and of course,the reactiontime would vary accordingto how much he or she had to drink.The circuitpresentedhere canbe built forjust a few dollars and an hour's worth of time.

The reaction-tirnetestercircuit (seeFigure7-3) probably looks similar to the c cuit usedin the previousexperiment.Thedifferencebetweenthe two circuits is simply a 10-LED bargraph display and two buttons.You shouldalsonote that thereisn't a power switch built into the application; I take advantageof the low-powersleepmode of the PIC16F684microcontroller aswell asits ability to run on the power provided bv two AA battedesThe button connectedto

t
140

l , e 3 P I C @l ' l C UE x p e r i m e n t s f o n t h e E v i I

Genius

RA2 will start the test,andthe button at RA3 is the userrespondbutton,which is to be pressedwhenthe userseesthe LEDS start to sequenceon and off. The operationof the circuit is quite simple,after power is applied(i.e.,whenRA2 is pressed),the circuit delaysat somerandominterval (usingthe current TMR0 value)betweenone and two seconds. If RA3 is pressedduringthis time,the test stopsand the two extremeLEDS startflashing.After the randominterval,the LEDs are sequenced on until RA3 is pressed. If RA3 is pressedduringthe sequence, the operation stopsat the currentlydisplayedLED. If the userdoesn't respond,then the lastLED startsto flash.The flashingLED(s) or just one LED will stop,and the PIC MCU will go into sleepmode after 1 minute unlessRA2 is pressedand anothergameis started. When I built rny prototypecircuit (seeFigures7-4 and 7-5),I useda basicprototypingPCB that had somegenericsignalandpowertraces,and then filled in with poinlto-point wiring for the remainder.WhenI wasfinished,I useda beadof Weldbondadhesiveto hold down the wires.Beforewriting the application,I createdtwo testprograms.Thefirst,which teststhe two buttonqis cReact1.c: ilinclude cReact 1.c - C Program /r on Reaction test€r ThiB

Prog!€m

l{42 RjA3 R,AO &A1 RiA4 RiA5 RCo RC1 . RC2 RC3 RC4 RC5 -

Buttoa Button I,ED1O LED9 LEDS LEDT IEDS IJEDs tEDll IJED3 LED2 I,ED1

is

a nodtification

Connectior Connection

to

TeEt

of

(Stalt/Porder (Reapond)

=-

while(1

(

r,

aA1 = AA2i RC5 - RA3i // elihw ) // End cReact ,

//

Loop

f,oteve!

// //

Po'lrer On switch Respond sxrilch

(to LED9) (to LEDI)

1

The secondprogram,"cReact2.c" teststhe sequenceoperationof the LEDS and wasbasedon "cPKLED.c": #include cReact 2.c - c Proglam tso T€st /* Connections on Reaction Test€! This

Plogra$

RAz - Button RA3 - Button RAO - I.ED1O RA1 - LED9 RA1I - I,ED8 RA5 - I.ED? RCo - tED5 RC1 - IJEDs RC2.IJED4 RC3 - LED3 RC1I - IJED2 RCs - tEDl

is

a rnoalification

of, ncPKLEDn

(Start/Polre! (Respond)

Connection connection

LED

On)

nyk€ predko 04.L1.28

IJED Buttons

"cBuEton" On)

( IN:IIO -CONFIG T'NPRCI'IECT \ & T'NPROIECT

int

i,

j,

& I{DITDIS & BORDIS

& PWRTEAI & IESODIS

& MCI,R.DIS

&

& FCTITDTS) '

k,

nain( )

t PORTA = 0x3Ft PORTC = 0x3Ft CTiICON0= 7, eNsEL = 0t TRISA = 0b001L00; TRISC = 0;

AI1 Bits are high because LEDS active // are negativ€ coinpalatols / / Truqt off off ADc // !u!n / / B A 2/ B A 3 a r e i n p u t a // A1,1, of PORrrc are outpula //

myke prealko 0{ . 11.2I

1 OL E D Bargraph

& WDIIDIS & PWRTEN & MCIRDIS & -CONFIG(INTTO I'ITPROTEC! \ a ITNPROIIECT& BORDIS & IESODIS & FCMDIS) t

nain ( )

t PORTA = 0x3Fi PORTC = 0x3!i CMCONo = ?, ANSEL = 0t TRISA = 0b001100, TRISC = 0,

ALL Bitsa are high becaus€ IJEDs // are n€gative active off comparatols / / Tnt // Tuln off ADc // aA2/aA3 ale inputa / / All ot PORTC are outputss //

ThisEnd Figufe 7-3

Reaction-time circuir

S e c t i o n5 e v e n S a m p I e C l ' il c n o c o n t r o I I e r

Applications

141

Rc{ = 0; break, case 2: RC3 = 0t break, case 3: RC2 = 0t break, case 4: RC1 = 0t breakt caae 5: RCo = 0t breaki case 5: Ria5 = 0t breakt case 7: R[4 - 0t bleakt case 8: Rl[1 = 0t breaki case 9: RlAo = 0t breaki // hctiws )

Fiqure 7-q The prototype retrction-testercircuit was built on a prototyping PCB

whiLe(1

(

== L')

//

Loop

(i = 0r i < 255r i++) // for for (j = 0r j < 429, j++r,

Sinple

PORTA - 0x3Fr PORTC = 0x3Ft

turn

switch

//

Forever

Delay

off

lJoop

LEDS

(k ) ll

LEDT

l/

LED2

Figufe 7-5 Backside point-to-point wiring used.on the prototype reaction-testercircuit

L42

I,ED3

//

LEDA

ll

LED5

//

LED6

//

r,E,D7

ll

I'EDB

//

I'ED9

//

t'EDrO

k = ( k + 1 ) % 1 0 i

{ cas€ 0: RC5 = 0, breaki case 1:

//

I ]

I / ell}:w // End cReact

2

After usingcReact1.cto verify the operationof the buttonsand cReact2.cto showthe LEDs werewired correctly,I createdcReact3.c,which is the reaction tester. In cReact3.c,you'll seea coupleof thingsthat won't be obviousto you.The first is the group of nestedfor loopsthat alsopolls button and falls out if a button is pressedunexpectedlyor out of turn.When you look at the loops,try to imaginetheir operation You with both the button pressedand with it released. can alsosimulatethis codeto seeexactlyhow it works by usingthe synchronousstimulusfunction of MPLAB@IDE. The secondpiecethat will seemunusualis the sequenceof instructionsleadingup to and following the SLEEP0;function.This is not a function,it is an assemblerinstructionthat causesthe PIC MCU to go into a low-powermode,or sleep,and it canbe awakenedeither by cyclingthe application'spower or causing an interrupt requeston RA2.There is quite a bit of theorybehindthe sleepoperationand the different modesthat can be employedwith it. Tiust me;the "INTE : 1;/SLEEP0;NOPO;"statementsequence will put the PIC16F684into a low-powermode and will resumeoperationwhen the RA2 button is pressed.

l , a 3 P I C @l ' l C UE x o e r i m e n t s f o r

the Evil

6enius

ExFeriment 5 2 - Floke nbuk@Monora i l/Traffic Lig htE

t PICI5F68 4 14-pin

socket

2 Red LEDS 2 YelLow LEDS 1 10 pF electrolyt

ic

capacito! 0 .01 ru,F capacitor tYpe)

(any

LDRs

DI'',M Needle-nose

p liels

Dremel tool

with

10k res istors 100 Ohm resistors

ablasive

t c^l

rari

n^

r F^n

1 Prototypinq

solder

1 Three-cell.

Wi.!e-w!ap

AAA battery

pack

vri!e

2 mrn heat-shrink

PCB

AAA batteries

tubiog

Weldboad adhes ive s-minute

epoxy

Crazy glue

My daughterand I love to play with our Rokenbok remote-controlbuildingsystem.The toy consistsof a numberof remote-controlconstructionvehiclesthat interactwith buildingmaterialsusedto createdifferent buildingsandstructures.Tohelp enhancethe experience,I wantedto modify a monoraiVtrucklevelcrossing so that dummywarninglightswould flashwhen a train approached(seeFigure7-6).This seemedlike a perfectprojectfor a PIC MCU I alwaysfind that hacking toys to be somethingof a challenge;the electronics built into the toys do not lend themselvesto intedacing with rnoregeneral-purpose electronics(generallythe electronicsselectedwere the lowestcostavailableand havetheir own specialcharacteristics), structuralfeaturesare difficult to cut throughor modify without significantlychangingthe look of the toy,andthe weight of the additionalelectronicscan seriouslydegradethe performanceof the toy.I canhappilysaythat this modificationwent quite well,with the only major surprise beingin the operationof the PIC MCU. The theorybehindthe modificationis quite simple. Two light deperulanrreslstars(LDRs) were placed at either end of the crossing,by solderingthem to cut down prototypingPCBsand gluingthe PCBSinto

S e c t i o n5 e v e n

trackpieces(seeFigure7-7).On powerup.it is assumedthat the train is not over the LDRs. and therefore they samplethe ambientlight eighttimesand averagethe result.When the train movesover the LDRs, it is assumedthat the ambientlight to them is c u l o f f a n dt h ec h a n g e i n t h eL D R r e s u h isn a c h a n g e in thevaluereadby the PIC MCU's ADC ot greater than 25 percent.Thiscausesthe LEDs placedin the vehiclewarninglights to flashfor aslong aseither sensor is coveredplus 10seconds. Despitethe simplicityof operation,the circuitworks very well and is actually quite impressive. Two nice thingsaboutthis circuit are that the LDRs do not needto be wired to specificADC inputs(either one will do) and,practicallyspeaking,LED colorsdo not needto be matched.Theseadvantages eliminated the needfor testingeachwire for a specificconnection, and thuseliminatedthe difficult task of sortinsout 10 two-foot wiresin a smalltoy. The installationof the LDRs is quite simple.The2footJong piecesof wire weresolderedto eachof the LDRs' leadsand coveredin heat-shrinktubing.I used the three squareblack structuralrodsfor the track and, usingKrazy Glue,I attachedthe PCBSto the insideof

S a m pI e C I ' il c r o c o n t n o 1 I e r

Applications

L43

l

CI .tJ

bt

,l.l

FI @

lr/,

CI *a 0, J1

g,

Figure 7-6 Rokenbokmonorail-levelcrossingwith train sensorsand flashing waming lights the middle squareof the structural rod. At this position, the monorailandits trailer would coverboth sensors I was surprisedto discoverthat Krazy Glue behavesasa solvent for the black plastic,literally weldingin the smallPCBswithout needof another glue. Red andyellow LEDs were installedin two warning lights that snapinto stalks.I did so by drilling % -inch holes in the plastic on one side and 1/z-inch holes in the other to allow the flangesof the LEDs to fit through and the endsof the LEDs to poke out the other sides.Like the LDRs, the 2-foot lengthsof wire were solderedto the LEDs, but with a few modifications.The cathodesof the two LEDS were joined with a 2.5-inchlength of wire, and single cathode wire was usedfor the two LEDs. I then soldereda 100f,)resistor

c{

Thia Program will fj.rat s.iq)le lhe erDbi€at liqht oa the two LDRa for 8 SEfiD1e6, 50 n6 aDart. WLth th€se Sarq)les, tshe cotl€ will er.€cute, waitilg for lhe SeEsors lo be cov€reil anal tb€n uicover€d. $!r€n 6itbe! i6 Cov€raeal (IJDR Vo].lage changea bL 25% o:. nore) lhen the LEDa f,Iaah. Ighen both are left flaEh uncove!€tl, the lighta for an aalalitional 10 B€coDils.

4yke p!6tlko 0{.11.30

g

(u

& WDTDIA & PWRTEN & IICIJRDIS -CONTIG(INTIO T'!{PRCIIECT \ & I'NPROTECT & BORDIS & IESODIS & FCMDIS} '

H

.Fl

$.1

X kl

*inclual€ cRok 2.c - RokenJroh ApDlLcation /*

PIC15F68{ Pl.nE: RAO - I,DRI RA2 - IJDR2 RCz - I,ED1 RC3 - I,ED2

rn

g g.

to the anodeof eachLED that had a 2-foot piece of wire solderedto it and put heat-shrink tubing over the length of the resistor and its solder connectionsThese solder connectionsallowed rne to easily identify which wire wasusedfor which purpose.A simpler method of keeping track of the wfting might have been to use different color wires. I threaded the wires through the structural rods and the bottom side of the crossing.Using a Dremel tool, I cut away ribs in the center of the crossingto allow the wires from one side to passthrough without causing the crossingto rock when a vehicle or the train went over it. Thesewires were held in place using s-minute epoxy. With the toy modified and the wiring in place,I then created a prototyping PCB with the circuit shown in Figure 7-8.The 10k pull-up resistors on the LDRs will convert the LDRs into a voltage divider circuit that can be measuredusing the PIC MCU's ADC This is actually quite a simple circuit, although you will find it quite difficult to wire using the different wires leading from the toy.When planning your PCB, make sure you keep the wires from interfering with the monorail train asit passesover the crossing. To test the circuit,I created a simple program (calledcRok 1.c)that simplyflashedthe LEDs for 30 seconds,and then I jumped right into the application (cRok 2.c):

Figwe 7-7 Monorail LDR soldered to a small pi.ece of PCB and glued inside the black monorail track (one on eachside of the tossing)

L44

int int int co!6t

i, j, k, LighbTiner, FlashTi.nert IiDRo, IrDR2t int

fiftynB

= 3333,

l , P 3 P I C @f l C U E x p e r i m e n t s f o n t h e E v i l

//

LDR Av€rage

//

50 mB Delay

Genius

Valuea

nair(

{ PORTA = 0, PORTC = 0, CMCON0 = 7, ANSEL = 0b00000101, ADCONo = 0b00000001t // Bi,E 7 5 // Bit ll BiE lt2 / / BiE L ll git. 0 ADCON1 - 0b00010000t TRISC:0b110011, = 0t = 0t

LLghtsliner FleshTine! (i

for

= 0,

i

< 5,

alrin of.f. CdrE aralora ADC ON RAO & RA2 llurn on lhe AIrC garnple Ir€ft ilustif,ietl Uae VDD - Chan'lel 0 Do Dot Stalt fur|t on ADC the clock as // g€lect EoBc / I // RC2 & BC3 ar6 IrED Driv€r6 Flashing Yet // Nothlag // // //

I.DRo = 0, f o r ( j = 0 r j

//

i++)

< 8, J++) //

DeLey Eo r.et Power

get!L€ i++) t cer BA0 risht Average

GODONE = 1, // sarDLe aAo ( IGODONE)t while IJDRo=LDRo+ADRESHt (i = 0r i < flftslzns, for i++), iof

LDRo=LDRo/gt

//

Ciel Average

ADCONo = 0b00001001, I,DR2 = O, f,or (i = 0r J < 8, i++)

//

Sample

//

c€l

GODONE = 1, ( t GOITONE), !rhi1€ LDR2=LDR2+ADRESHt (t = 0, i < fiftt'nsr fo! I // to€ IJDR2 = IrDR2 / 8t (i - 0r i < fif,tt'mar for

//

Saq)le

J = 0t $hL1€(1

-=

1)

i f ( j < 2 )

R€ailiDg

on ItA2

RAo Lighl

Av€rage

RAo

i++)t //

cet i++),

Averag€

R€ading

//

uE6 J fo! chatulel se1€c! Loop Eorev€r

//

ItAo Read

//

(

{

if

(LightTilne!

l=

0)

Stsi11

//

!=

O>

ll

Chang€

TU |"{

FLa8hiag?

f",.

- 1t = LightTiner LighlTimer if, (0 == LightTLn€r) Elashlng // Finisheal | = 0, FlaahTlner // Finish€d PORTC = 0t J // fi

(LightTlm€r

= FLeshTimer FlaahTimer (0 == Flashtiner) lf | //

-

Flashingl

tst

ELashing?

Ul h3

1i

I

t

la{

When I createdcRoc2.c,I expectedit to work with minor tweaking. I was surprisedto discoverthat when power was applied, the LEDs flashed continually.This is probablythe most dreadedsituationimaginable;I had a problern with a hardware devicethat was not supportedby the simulator(whichhad worked correctlywhenI simulatedit), and I had not designedany way of passingdata out of the application.After about 3 hoursof working at characterizing the problem,I discovered that to get an accuratereading for comparison to the averagevalue,the ADC neededa dummy read after changingchannelsWhen you look at this code, you'll seethat I actually loop through eachADC's channel twice before I comparethe result to the averasedamountfor the channel.

{

A.DCONo= 0b00000001r // fo! (i = 0r i < flft!'nsr GODONE = 1t // ( IGODO$E) t wbj.le k = (I,DRESH a 100) j a j + 1 , ,

/

) elEe

serI)].e on RAo i++)t Do aDc Reaal

LDRot // Incr€{reat //

g€.nE)l€

sarE)le

on RA2

t ADCONo = 0b00001001, // S€4p1€ on RA2 (i = 0r i < flfllmsr for i++), GODONE = 1, // Do A.Dc Reaal ( IGODONE), nhil€ k = ( A D R E S H * 1 0 0 ) I LDR2I j = (j + 1) % {, , // ti

if |

((0 == (j & 1)) && ((k > 12s) ll (k < 7s))) Flashi'lg // Start/conlinu€

'Len Tfain Signal

Figure 7-B

"Righl'Tmin Signal

Traincrossingcircuit

S e c t i o n5 e v e n S a m p1 e C l l i c n o c o n t r o l l e r

ftl v/!

tld

Chans€ Flaahing Ligh!s = 10r FlaEhTirn€r // Res€t F1aah Tiner PORTC = PORTC ^ 0b001100t , /t fL | // fJ\ / / elilLv ] // Ena cRok 2

{

//

if

10 gecoDtla

{

i < flft!'nEr

,

= lO + 2Oi // Flash f,or (PoRTc & 0b001100)) Start | // If Not Flashing, PoRTc = 0b001000t = 10, FLasbTinler | // ti ll Ei l IJighlTiner (0 :E if

)

Applications

145

rl

tn ry *r.a

n

?r L

r",

To find the problem,I first simulatedthe application to make sureit worked asI expectedit to.You will find that the simulatorexecutesstraightthroughthe ADC operationswith the GODONE bit beingimmediatelyresetafter it is set.Using the Watchwindow registervalueupdatefeature(double-clickon the register'svalueto bdng up an edit window),I testedthe applicationfor differentADC return valuesand made surelhat the codeworked properly.Next,I commentedout all the codefor one of the two channels and I found the applicationstartedworking,until I returnedthe commentedout code.Next,by flashing the LEDS,I output the valuereadversusthe value averageand discoveredthey were different.Finally,I

tried to do a dummy readof the ADC channelbefore the live read,which wascheckedagainstthe averaged value. The previousparagraphdoesnot conveythe frustration and annoyanceI felt in working throughthe problem.But, by working stepby step,ensudngthe programworkedin the simulatorasI expected,checking my assumptions rigorously,and not presumingthe root causeof the problembeforehand,I wasableto debugthe application.This is a usefulsequenceyou canusewhenyou are facedwith an applicationthat doesn'twork or behavesin a mannerthat is totallv unexDected.

ExFeriment 53-5even-5egmentLEDThermometer

P I C 1 6 F 6 84 ?4HCT138 three decoder 1 14-pin

to

e j,ght

socket

2N3906 bipolar transi stors

NPN

(Radio Shack Thelmistor 271-110 recor nended) 0.01 pF capacitols tYpe)

DMM Scientific

100O res istors

calculator

330f,) res istors

Needle-nose pliers I

So lde r 9lire-yr3p

10k, 1-percent ance resLstor

tole!-

SPST switch 9i36

fwo-cell c1ip

Weldbond adhesive

Probablythe mostpopularPIC MCU projectI have ever designedwasa three-digitdigital thermometer for the PIC16C84that waswdtten in assernblylanguage.For somereasonthis circuit and softwarewas extremelypopularandwasusedasthe basisfor a wide vadetyof differentapplicationqincludingmonitoring the temperatureof a chickenincubatorlThe original digital thermometeruseda timed I/O pin resistance measurementof an RC network.Two input pinswere usedto calibratethe thermometeroutput,andthe calibration valuewassavedin the data EEPROM of the PIC MCU. The originalcircuit works quite well,but I wantedto eliminatethe needfor the calibrationvalue

L46

(any

AA battery

aswell aswrite the applicationcodein a high-levellanguagethat did not obfuscatethe operationof the thermometer.Tomeet theseobjectives,Iusedthe PIC16F684's ADC alongwith the PICC Lite compiler languageand its floating-pointnumbercapabilities. The circuit (seeFigure7-9),althoughfairly complex,is quite straightforward.One commonanode, seven-segment LED displayis activeat any one time, and the applicationsequences througheachLED display 50 to 64 timesper second,givingthe appearance that all four are activeat the sametime.The seven-segment LED displaysare poweredby PNP transistors

l , P 3 P I C @l ' l C UE x p e r i m e n t s f o r

the Evil

6enius

G1 Vdd

Ptc1 6F 684

B

C

.G2A/B Y3 \2 Y1 YO

RA5 RC5 RC4 RC3

-l-

RCI RA4 RCO

I

-L ,: Figure 7-9

"o

2x Dual7-Segment Common Display

Digital thermometer circuit

that are,in turn, drivenby an eight-bitdecoder.This may seemlike an ungainlymethodof driving the seven-segment displays,but it is requireddue to the lack of availablepinsfrom the PIC16F684to ddve the segmentcommonpns. I built my prototypeon a fairly smallPCB (seeFigure 7-10)and usedpoinlto-point wiring to createthe circuit asshownin Figure7-11.Thereare a lot of wires to solder,and whenyou havecompletedthe circuit,I suggestyou testit with cThermo1.asm.This will initialize the PIC16F684and displaythe ADC valuefor the resistor/thermistor voltagedivider.I usedthe Radio Shackthermistorbecauseit is reasonablypriced and the backof the packageliststhe thermistor'sresistance for differenttemperatures, which is nice to havewhen debuggingsoftware. *inclutle cTherno 1.c /. This program will ADC Value on four Displays.

Display

the

ADC Value

alisplay the curlent PrC16F584 7 gegnent Conmon Anoile LED

The Codle/wiring is baseal on 'c4x7s€9.c" Noting that Negative Aetive LED Wiiirlg iB useal. Eartlware AA5 RC5 RC4 RC3

-

Fiqure 7-10 Digital thermometertop with thermistorby the on/off switch RC2 - Segment RC1 - Segment RC0 - segment RAO - Right - Left

e f g

7 Segtnent 7 Segment

Display DispLay

lryke prealko 04.12.23

Not€s:

Segment Segment Segment Segment

a b c al

-CONFIG(INTIO UNPROTECT \ & ITNPROTECT

& WDTDIS & BORDIS

S e c t i o n5 e v e n S a m p1 e C l "ilc n o c o n t n o l l e r

& PWRTEN & ITCIJRDIS &

IESODIS

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CI,

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{l rn I

rn !J'

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--l $..1 \u P{

= (DtEplayIJED

NoPOr (1. = 0r fo!

Figure 7-'f'f Digital thermometerbacksideshowing pointto-point wiring

Eotevei

j

E j

for

/ / veed

fot

+ 1'

(s0 =- i)

if

(

+ !,

// uged L < 32"1, i++r,

NOP O T

Fl l{

l2oo!,

* 4)) = (DisDleyvalue >> (DiEplat'!@ & 0x0Ft PORTA = ( (LEDDigit lDisp1a]'Digitl >> 1) & 0x020) + (1 << 4) + (3 - DiEI)IayLED) t PORTC = r,EDDigit [DiEplayDigitl t DiEDlariIrED

Lr

"P

| /

Diq)IatDigir

o

trl

// //

Seatt. Dl.splayl.ng at 0x0000 DisDlay the 16 filgts slalt counting at zelo

//

== 1)

while(1

t

Oi

= 0t

Disl,laylED j = 0t

(,

n

-

DisDlatvalue

${

j - o;

% 4t

//

Ne*E Digrit

5 ms Timinsl // 5 ma Delay Loo9 5 ms Iimingl

// //

rncldrent !h€ couat€r? 1/{ Secolal Paaaeal?

//

R€set for geconal

anothe!

1/4

awl.tch(aDcstsat€) lnE lnt

DLapla!ryalu€, = o, ADcstate

DLsplalrDlgLt,

(

DlEplayriED,

case 0: // gtsart ADc operation CiODONE- 1t ADCSlat€ = Li bleak; ca6e 1: = 0t ADCSlate = (.a.DRESH<< 8) + ADRESIJt DiaDlat4talu€ b!€aki ] // hctiws

= { conEu char IJEDDigittl // RRRRRRR . PIC16F581I PIN // ACCCCCC / / 55432LO - IJED Segrlent // abctlefg

0b0000001, 0b1001111. 0b0010010, 0b0000110, 0b1001100, 0b0100100, 0b0100000, 0b0001111, 0b0000000, 0b0001100, 0b0001000. 0b1100000, 0b0110001, 0b1000010, 0b0110000, 0b0111000)t

| |

natn( ) t PORTA= O' PORTC= 0, CMCONo= 7t AI,ISEIJ= 1 << 2t AItCONo = 0b10001001, / / BfiE 7 // BLt 6 ll BiE 4.2 ll Bft L // BLE O A.DCONI = 0b00010000r TRISA = 0b001100, TRISC = 0b000000r

X

/ / 'r\lzn off comparatorE // 8A2/ (AN2) la a.|t Analog Input // $rr|t on the ADC .IustifL€d Right S€lnlrle u6e rrDD - Chaanet 2 Do not start Tuln or ADC the Clock as // 5€1€ct Fosc/8 // RA5/RA1/RAo a!€ outl)uld of PoRTc ar€ // ALl Bits outDuta

/ / et"rbw / / E^d cTherno

1

When cThermo 1.cis running, you can test the operation of the ADC and the display by breathhg on the thermistor or by putting it in the sun or in a refrigerator. After you have verified the operation of the display and thermistor, I suggestthat you coat the back of the PCB and all the wires with Weldbond or epoxy to hold them down and prevent them from being damaged. The next program demonstratingthe operation of the circuit is cThermo 5.c,which displaysthe current resistanceof the thermistor(in 10Oincrements).I found that the resistancedisplayedwasalmostexactly the resistancespecifiedon the back of the thermistor's package. The thermistor and 10k, 1 percent resistor form a voltagedivider,which is read by the PIC MCU's ADC. The formula for the 10-bitADC value(assumingthat the full range is 1,023)is asfollows. ADC/

j.,023 =10k/

(10k + &n"_,*",)

Rearranging this formula, R*"-'.,o. can be calculated as:

|lI

148

l , e 3 P I C @I I C U E x o e n i m e n t s f o r

the Evil

6enius

&**'"-.=t(1,023x10k) /ADcl - 10k This is the formula usedin cThermo 5.c to calculate the thermistorresistancevaluebeforeit is converted to indiyidualdecimaldigitsand displayed.I broke the formula into different piecesand put them in a state machineto makesurethat the floating-pointoperations would not delaythe operationof the TMRObaseddigit displaycode. cThermo 5.c wasmy first experiencewith floatingpoint numbers and variablesin the PICC Lite compiler, and I mustsayit wasan educationalone.In the codefor cThermo2.cthroughcThermo4.c,I tried a number of different approachesto solve the problem and discoveredsomethingthat shouldhavebeenobvious.The functions that provide floating-point operators in the PIC MCU take up a lot of instructions.I found that to bestimplementthe PICC Lite compiler codewith floating-pointoperatorEI shouldrestrictthe numberof operationsto three. In the previouscode,you will seethe three operators: . .

Floating-point-to-integerconversionusingthe "(int)" type cast Floating-pointsubtraction

.

Floating-pointdivision

To convertthe thermistorresistanceto a temperature, I found that the resistancevaries negatively with the temperature.This was confirmed by a table on the datacardthat camewith the Radioshackthermistor. This meansthat asthe temperatureof the thermistor goesup from a nominaltemperatureof zs"C,the goesdown.Similarly,when the temperature resistance of the thermistordrops,its resistanceincreases. With a little bit of experimentation with a calculator,I discoveredthat the resistancevariedby 1.039percentfor everydegreeCelsiusof temperaturechange.This relationshipseemedto be true for +/-40"C from 25'C, which waswithin the range of temperaturesfor a thermometerto be usedaroundthe home. When you order a specific thermistor, you can find this informationin its datasheet, otherwiseyou will haveto comeup with somekind of way of experimentally finding this information. This is not easyto do. The temperature versusresistanceinformation printed on the packagingis why I selectedthe RadioShack part.Whenyou look at the datasheets, you'll seethat the percentresistorchangeper degreeCelsiusis not constantacrossall temperatures,and the manufacturer will often include a formula for a temperature range of severalhundreddesreesCelsius.

To keepthe applicationreasonable,Ijust kept the operatingrangeto +^ 40"Cwith a centerpoint of 25"C and cameup with the voltage{o-temperature functionfor the thermistorand 10k,1 percentprecisionresistorvoltagedivider: = Vdd X 10k/(10k

Voltage*,

t$ fit

* &n"-r"-.)

BecauseI usedthe full 10 bits of the ADC for this application,the ADC valuecouldbe convertedto a voltageusingthe following equation:

t**

tr1 p.{

f&

VoltageRA2 = Vdd X ADC/1,023

And combining them, I could solve R*"**o, from the ADC value:

I11

Vdd X ADC/1,023 = vdd X 10k/(10k R*.*;**)

t6

Rrr,._i"rc, = ll1-,023

X 10k) /ADCI ,

+

10k

tflr

This calculationis carriedout in states65 and 66 of cThermo5.c. The next step was to convert this resistanceinto a temperaturechangefrom 25"C.Knowing that the thermistor'sresistance changedby a setpercentfor every degreeCelsiuschangein temperature,the resistanceof the thermistorcouldbe expressed as:

{u -\ l!l lqE

* { f l

ti, = 10k x

&h"-t"t.'

(1 039'5"c r)

9{

Pluggingthis valueinto the ADC equationfor Rrh"*nto.,the temperature difference from 25'C could be wdtten out as:

t i.F .J

t ( 1 , 0 2 3 x 1 0 k ), / A D C-I 1 0 k = 1 0 k X (1.039,soc a)

F

Removingthe common10kterm,the equation becomes: ( 1 , , 0 2 3/ A D ' c ) - 1 =

1 . 0 3 9 ' 6 k- r

=

e1n(Nu)

n |"{

Now, dependingon how much mathematicsbackgroundyou have,this may seeminsolvable.But, by knowingthe following: NunPowei

Frl

o

h{

t

x Pawer

o

5

o

$ tv F'

S e c t i o n5 e v e n

S a m pI e C l l i c r o c o n t r o l l e n

Applications

149

wheree is the baseof the naturallogarithm(ln), and by usingthis relationshipon the previousequation, alongwith a bit of algebra,you can find: Temp = 25oC - {Lnt (1,023IADC) 1ll1n(1.039)]

Even if you understandexactlywhat I've donehere and havehad the necessary instructionin algebra,relations,and functions,I'm sureyour brain is hurting.I suggestthat you standup and take a break.I know I had to.The temperatureformula is deceptivelysimple: It took me four daysto work throughthe circuit and equationsto comeup with this equation,which is specific ro the PIC16F684's10-bitADC andindependent ofVdd. Calculatingthe temperatureusinga formula that is independentofVdd allowsthe circuitto work with differentvoltagepower supplieswithout having to changethe software.It is actuallyquite an important featureof the formula. It seemedlike a crueljoke to me,but the worstpart of developingthe applicationwasyet to come.Despite havinga seeminglysimpleconversionformula,I found that I had a fairly serioussizeproblem;the code seemedto be 100to 110instructionstoo largefor the 1024instructionsavailableto the PIC16F684PICC Lite compiler. The problemwith the codesizewasthe needfor includingthe C naturallogarithmfunction (known as log in C,not ln asis normallyusedin mathematics). This functionseemsto take over 400instructions,and I couldonly allow 300or so.I wasvery surprisedat this situationasI believedthat the naturallogarithm(and exponent)functionswererequiredfor the floatingpoint divisionoperator.Further complicatingthe situation wasthe fact that the MPLAB IDE simulator continuallyflaggeda subroutinereturn underflow beforeexecutingthe applicationcode. It took me anotherthreedays,but I wasableto get the applicationworking for the previousformula.By carefullymanagingintegervariablesizesand looking for opportunitiesto shareapplicationcodeasmuch as possible,I wasableto shoehornthe applicationin, with a dozenor so instructionsto sDare.andit seemedto work. cThermo6a.cis a modificationof the final result, and I found that the digitswould occasionallyflash noticeably.I madethe assumption, first,that the log (C

150

naturallogarithmfunction)took longerthan the 4,000 cycles(4 ms) availableto it betweenLED display updates,and then I enabledthe 8 MHz clock and doubled the numberof cyclesbetweenLED display updatesso the 4 ms delaystayedconstant. Looking at the work that went into this experiment, alongwith the trials and t bulationsI had to endure, you're probablyaskingyourselfif the effort wasworth it. This is an especiallygermaneconcern,considering that I couldhavespreadit out into threeexperiments: LED Ohmmedriving four displays,a seven-segment thermometer. I would haveto ter, and the final digital sayyes,becauseit gaveme somepracticalexperience with floating-pointvaluesin the PIC MCU and, despiteall the problemsI encountered,the voltage-totemperatureformulais fairly easyto observeand checkvisually. I wasableto comeup with the following ruleswhen workingwith floating-pointoperationsin the PIC MCU: .

.

.

r

Limit the number of floating-point operations you are going to useto three:subtraction,division,and floating-point-to-integercasting. Do not use any ofthe logarithm or trigonometric functionsin a PIC MCU where only 1k of programmemory spaceis availableunlessyou absolutelyhaveto. If you are running displayloops with floatingpoint operationsexecutinginsidethe delays, recognizethat the floating-pointoperations take a lot of time,and plan accordingly. Do not obfuscateyour floating-pointcalculation codein order to make them more efficient. If you are going through the effort of including floating point in your application,make sure the theory behind the floating-pointoperations is soundand the formulasand algorithmsyou are implementingare reducedasfar asreasonably possible.Try alsoto avoid many of the conversionsand leapsthat are necessarywhen fitting integer operationsinto a task that requiresdata manipulation.

l , a 3 P I C o I I C UE x o e r i m e n t s f o r

the Evil

6enius

Experiment sr-.|-PlCMfU "Piano"

1 P I C 1 6 F 6 84 1 14-pin

socket

1N914 silicon t

diodes

0 ,47 ItF capacitor tYPe)

(any

0 . 0 1 p F capacitor tYpe )

(any

10k resi stors Dl''!M

Piezo speaker

Needle-nose pl iers Soldeling

1

iron

I

Solder Wire-wrap

wire

IodelibLe

ink

Three-cell clip

AA battery

3 AA batteries malke!

1 Prototyping

PcB

Weldbond adhesive

In Figure7-12,you will seethat I havearranged10 momentaryon pushbuttonsin an arrangementthat is similarto a piano'skeys.This probablydoesn'tseem like suchan amazingapplication;the PIC16F684has12 pins and 10of them couldbe easilyconnectedto individualbuttons,leavingtwo pins for driving out the musicalsignal.In the previoussection,I introduced you to switchmatrix keypads.So you might think that the 10keysare wired asa switchmatrix,resultingin only seven(five columnsof two rows) pinsbeingused. Actually,neithermethodis used.Instead,the wiring usedin this applicationrequiresonly six wiresto interfaceto the 10 buttons.If you havea smallnumberof button inputsfor an application(andyou have designedit to work with only one button at a time pressed),you will find caseswherethis is the mostefficientmethodof widng your application'sbutton input. The methodusedto providethe 1O-buttoninput can be seenin the piano'sschematic(seeFigure7-13).For six of the naturalkeys,thereis a traditionallypulled-up momentaryon button.However,for the four sharp keys,a momentaryon button connectsthe adjacent naturalkeysto groundthrougha silicondiode.When the sharpkeysare pressed,currentwill flow through the diodes,pulling eachof the adjacentnaturalkeys low.Therefore,to sensewhen a sharpkey is pressed, the two adjacentnaturalkeyshaveto be polled.

This methodcanbe usedin a numberof different applications. Rememberthat you are not limited to wiring the in-betweenmomentaryon buttonsto just two standardpulled-upbuttons;youcan usethis methodwith really any numberof standardpulled-up buttons.ln doing so,you will discoverthat locatingthe multiple diodesfor eachbutton in betweencanbe a problem.I am bringingthis up becauseit wasa bit of an issuefor me.However.I wasableto find a

Fiqure 7-la

PIC16F684-based I0-note "Piano"

S e c t i o n5 e v e n S a m p1 e C l ' il c r o c o n t r o l l e r

Applications

151

_:'-r' __L

Figure 713

o c(d .F{

A

p U

E

U H

A

I
c (l

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o

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Piano circuit

prototyping PCB that would allow multiple connections at a singlepoint, and by experimentingwith how I placed the pull-up resistorsand the diodes,I was able to come up with a schemethat wasquite easyto wire and did not useup an excessive amountof space.In Figure7-14,I showhow the diodesare wired to the backsideof the PCB underneaththe naturalkev buttons. cPiano.cis the application code I came up with for this expedment and it delays50 ms and then polls the six input pins to seeif any buttons are pressed.If a pin is pressed, then a PWM period and duty cycleis saved in the TMR2/CCP hardware and pin RC5 is put into outputmodefor the PWM signalto passthe soundto the Piezo speaker.To corneup with the delay periods,I started with a table of the different note frequencies.I then converted them into microsecondperiods and dividedthem by four so they couldbe loadedinto the PR2 register for driving out the different frequencies. You'll find that the final output may be a bit flat or sharp;this is due to roundingerrorsthat camewith converting the periods into integers that TMRZ could work with. *itlcluae /* cPLano.c - 10 Not€

Thl"a aDDllcation noaLtorE 10 Diano keys via 6 I/O Dina anal Dlaya th€ aDprolrliale note aB IoDg aa lhe k€y La pleEsea[ for 50 ps incr€meata. Th€ PRU outDut ia u6ed for the nolea !,rith a 4x Drescale!.

fsl 152

Ez Hz vz Hz Hz Hz Hz Hz

- RAo/RAl - RAo

G* A

-

L,662 1,750

-

955 902 852 8O2 758 715 675 638

ps ps p,e p,a pB rlE pB Es

- P P = 2 4 0

-

602 pa 558 ps '

PP = 150 PP = 1{2

Nolea: PIC15F58{ Rutrning at { uEz with Iut€rnal oEcLllalor RC5/P]-A - Pw!{ RC2:RCo - Soulal InDut BilE Notetl Ab<w€ RA2:RAo - Souril Input Bils Noteil Abov€

rvke Dreflko 05.0L.22

-CONFIG ( INTIO & WD4IDIS & PWRTETI & MCIJR.DIS & I'}IPROTECT \ & ITNPROTECT& BORDIS & IESODIS & FCMDIS) t

int jt char Ke!ryaluei char Freqoutst tnain ( )

t

rrhil€(1

(

== 1)

NoPO r lor (f = ui NOPO,

ll // ll ll

rI\En

//

Loop

//

50nE D€lay

(0 == (K€Walue Lf (0 != (Kewalu€ = 1{2r Fleqout €1ae

Freqout

oft CdE)aratora truln off AIrc r|/ ,F.,2 ',aa 4r. Preacal€r E,nable PDU Oulput Forever

7 < 4555i 7++)i

= ( (PORTC & 7)

Ketrvalu€ if

- P P = 2 0 0 - P P = 1 8 8 - P P = 1 8 0

rrz Hz

garalware

C!'ICONo = 7t iNSEI = 0t E2CON = 0b00000101r CCP1CON - 0b00001100t

"Piano"

The Keya are alefineal as: !'liild].€ C - RC2 - 1,0{5 - RC1/RC2 - 1,108 C* - RC1 - L,L74 D - RCo/RC1 - 7-,248 D* - Rco - 1,318 E - RA2 - 1,395 F - R-e1/RA2 - 1,d60 F* - RAI - 1,558 G

Figure 7-lt{ Backsideof PIC16F684-based piano showinghow the diodesare wired underneqththe buttons

<< 3)

+ (PORTA & 7);

& (1 << 0))) & (1 << 1) ) ) // A

= 150,

t/ e*

(0 == (Ket^Ialu€ & (1 << 1))) elae if (0 != (Kewalu€ & (1 << 2))) if

l , e 3 P I C @l l C U E x p e n i m e n t s f o r

the EviI

Genius

= 150r F!€qoul // els€ , Fleqout = 158i // F* else if, (0 == (K€]|value & (1 << 2l)l = 180r Fleqout // (0 == (Keyvalu€ << 3) ) ) else if & (0 t= (Kefltalue & (1 if 4))) Freqout - 188i ll F eqout = 200r // (0 == (Ket4/alue elEe if & (0 l= (Kewalue if & (1 F!€qouts = 212, // elEe FreqOuE = 225, // (0 == (Keyvalue & elBe if Fr€qoul = 240r // elBe / / Er€qouts = 0,

D* (1 << 4)))

(0 == Freqout) tf TRISC - 0x3F, elEe

Nothing Presaetl Tuln OFF Output setup PwM

ltRISCs = 0r // fi ) // €lihw ) // Enal cPiano

D

(1 << 5) ) ) Presaeal

{ PR2 - F!€qout t CCPR1L-F!€qOu!/2t

Ouqntt 50% Dtrty Pwu sigrnal

Signal

'iJ

I shouldpoint out that this circuit is not limited to only 10pins.For my application,the limiting criterion wasspacefor buttonson the prototypingPCB.Using this method,if I had usedall 11 availablepins on the PIC16F684,Icouldhavesupportedup to 22 keys.This is a goodmethodto rememberwhenyou havea fair numberof input buttonsto poll but don't want to go throughthe hassleof the switchmatrix code.Generally,this schemerequiresone-halfthe buttonsasI/O pins,andit canbe extendedfar beyondthe 10 buttons presentedin this experiment.As a point of reference,it seemsthat 20 is the numberof buttonswherea switch matrix keypadis more efficient(in termsof I/O pins) than the methodDresented here.

s )) )

Nothing

Output

//

j

5-l t,:t .al

i-f

i ?i!

I

Cycle

Experiment 55-Model Flailurag Suritchfontrol ',AJ

1 PrcL 6F68 4 1 14-pin

'i.r;

socket

fRIACs (Radio Shack 276-1000 reconmended) 1 5.1V,

1 Anp Zene! diode

1 lN9l4

silicon

0 . 0 1 / u , Fc a p a c i t o r tYpe)

Osci lloscope

Soldeling

1 2204, p Iie!s

NeedIe-nose

wire

1 Two-position block

HO scaLe remote tlain switch

Thlee-position block

flain

Prototyping

supply

(any

a"

resistor

;

1

poi.e!

i.,"*4

les istor

iron

SoIder Wire-wrap

1 l0k

!-watt

g'

diode

1 330 pF electrotytic capacitot DMM

*",i,

telminal

td

terminal PCB

r.{ Comparedto other hobbies,model trainshave changedvery little sinceI wasa kid.When I go to a local train store,I'm alwaysdepressedto seethat powersuppliesare still basedon a Variac(variable transformer)train Dowercontrol and a transformerfor

S e c t i o nS e v e n

18-VoltsAC accessory power.I realizethat the DCC systemdoesbdng the hobby into the twenty-firstcentury,but thesecontrolunits aswell asthe remoteunits are very expensive. What is neededis a low-costway of providingcomputerizedcontrol of trains and the

S a m p1 e C l ' li c r o c o n t r o I 1 e r A p p l i c a t i o n s

L53

ra . , fi

I

r!

*P

J'l

tu r-{

iq

& , t!

IJJ

layoutsso that hobbyistsof moderatemeanscan experimentwith computercontrol of their layouts.In this experiment,I will showhow a PIC microcontroller canbe usedto control a switchusingthe accessory power from the standardtrain power supply. Before goingfurther,I want to note that this ctcuit is powered by a/renrating current (AC). The AC usedin power this experimentis the benign18-VACaccessory available from a hobby train power supply.The circuit'spower supplyis not designedfor usewith household AC (110or 220volts dependingon whereyou live),which canbum or electrocuteyou.Although the methodsusedto designthe power supplyare the same, and I show how I calculatedthe valuesfor this experiment,the componentvaluesare not valid for household AC. If you want to interface your application with householdAC power (or anyAC voltagesother than the 18volts usedin this experiment),makesureyou consultwith an engineeror electricianbeforeconnecting the circuit to the power supply.Be sure you have selectedcorrectvaluesandhavewired the circuit accordingto your local code. The controlcircuitis quite simple(seeFigure7-15), and I was able to wire it on a small prototyping PCB (seeFigure7-16).ThePIC deviceis poweredby a 5.1volt Zener diodewith a 220Oresistorand standard resistorto rectify and regulatethe current.The 330pF capacitorensuresthat the voltageis smooth.ThePIC MCU continuouslypolls the SPSTswitch,and if it changesstate,one of the two TRIACS is drivenfor a few millisecondsto changethe solenoidin the track switch.If you are wondering,the applicationcould be easilyexpandedto handlemultiple switches. Although dueto someof the issuesthat I had.there are some considerations that you shouldbe awareof that I will sharewith you at the endoI theexperiment. To calculatethe valuefor the components, I assumedI would run the PIC16F684at 5 volts,so I useda 5.l-volt Zener diode (whichhasa constant5.1 volts acrossit) and a silicondiode and resistorto rectify and limit the curent flowing through the circuit. The RadioShackTRIACs I usedrequire25 mA of current to operate,so I wantedto havea maximumof 50 mA (25 mA for the TRIAC and25 mA for the PIC MCU and other components). To find the correctresistor value,I usedKirchoffs and Ohm'sLaws:

= 12.2 volts

/ 50 nA

= 244Q

I useda 220.0resistorin the circuit becauseit is a standardvalue.For its power rating,if 50 mA is passing throughthe resistor,0.55wattsof power is beingdissipated.Toensurethat therewouldn't be any power issues, I useda 1-watt-ratedresistor. With the powersupplycircuitryselected,I built the cfucuiton a prototyping PCB using small terminal blocksto connectthe c cuit to the 18-voltpower supply and to the train switchusingthe wiresthat come with the train switch. (For this, I bought an ATL RemoteRight-HandSwitch,item number851.)Before burninga PIC MCU with code,I testedits operation by shorthg pins RC4 and RC5 to ground to make sure the TRIACs (which are simply AC switcheqcontrolled by current)would changethe switchsolenoid'sstate. In my application,I kept the I/O pins driving the TRIACs in input modeuntil the solenoidwasto be driven. When I tried the PIC16F684in circuit,I found that the circuit worked fine to changemy switch to one state,but had problemswith the other state.In this state,the switchwould start chattering,and the soleprobe on noid got very hot.When I put an oscilloscope the I/O pins,I discoveredthat both of them were becomingactive.Further investigationrevealedthat the solenoidstateseemedto require so much power that the 18 volts ofAC wasreducedto zero.After consideringthe problem,I decidedthe simplestsolutionto the problemwasto usethe PIC16F684'S EEPROM datamemoryto savethe stateof the switchin casethe PIC MCU wasreset.Thiswasa fairly minor modification to the originalcode,and I calledit ci[rainz.c: #incluale cTraln 2.c - controL /*

Ac Dliv€n

Train

control

This Drogram ia a modlif,ication of "clrain" Eo take adlvanlag€ of, the EEPROM Data lilemory !o recoral the laal aelting of the PIC Elritch RA3 - Button CoDnectioa RC4 - Train 1!RIAC1 RC5 - Train TRIAC2 ntzke Drealko 04.12.30

!tr VAc = V-{zener}

+ Voi"a" + Vn."*.". (J

H !d-.!

;€

= 5.1 volts

18 volts

+ 0.7 volts

+

I

V"""r".". Vnesistor= 12.2 volts R = V / I

154

AC Common

Figure 7-'15 Train

1 e 3 P I C @l l C U E x p e n i m e n t s f o n t h e E v i I

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( ( i < 1100) && (0 == RA3)) while ( 0 r = P"A3) if Bounce // switch else Debounce // Increment = 0t Bstale EEPROM WRITE (4, f o r ( i = 0 t i < TRISC4 = 0i f o ! ( i = 0 i i < TRISC4 = 1t

] else

if

((0

Active state // rnalieale 0)r // a.ecofil in EEPROM 5555r i++) r // 100 ns // Enable RC4 as Output 5565r i++), // 70O ne Dliwins Solenoid // Finished

!= RA3) && (Bstate != 1)) // Sttr'ilch chaflge

{ Fiqure 7-16 Sintplehobby train switchcontrol ctrcuit thot replacesstandardmechanicalswitchblock

& WMDIS & PIIIRTEN -CONFIG(IIIIIO UNPROTECT \ & T'NPROTECT & BORDIS & IESODIS

Bs€ate

int

& IICI,RDIS

Debounce Count€r i = i + 1t // Itteremen! state Active Bstate - Lt // halicatse irr EEPRoM | / 'tecord, EEPROM_WRITE ( 4 , 5666r i++)r // 100 ns f , o ! ( i = 0 t i < TRISCs = 0t // Elable Rc5 as Output 5666r i++)r // 100 ns f o r ( i - 0 t i < solenoid TRISCs = 1t // Finished Dliving // fr J // el-ihw ) 2 I / E']A cTrain J

&

& FCMDIS ) i

= 2t

tnain ( )

{ PORTC = 0t CltlCONo = ? t ANSEL = 0;

Output BitB are ].ow turn off Conll)alatol.s Turn off aDC No output6 {Yet) i++) // 250 ms Initial f o r ( i = 0 t i < Delay ( (EEPROM-READ( 0 ) == 91 ag if (EEPROT''READ(1) == oxFF) && (EEPROM-READ( 2 ) == 0x55) && (EEPROM-READ( 3 ) == 0tAA)) = EEPROM_REiAD( 4 ) t Bstate the Slate // rnitiaLize // // // // 18000r

t EEPROM_WRITE(0, EEPROM_$RITE ( 1, EEPROM_I{RITE( 2, EEPROM,WRITE( 3, EEPROM-VTRITE( 4, // fi , while(1

t if

((0

== L)

O) '

//

Put

oxFF) t O'.55) ' O:.AA)' 2) t

//

Nolhing

ll

in

Check

set

Loop Forever

== RA3) && (Bstate

I= 0))

//

$titch

wbile (( i < 1100) && (0 != RA3)) ( 0 = = R A 3) if Bounce // switch

Y€t

When you build this application,you may find that you do not needto savethe stateof the solenoidin EEPROM datamemory.I havetried this application on only one train switch.As the sayinggoes:YMMV (1tourmileagemay vary).You may find that you requirethe EEPROM for both solenoidstatesor you might find that you don't requireit all. This applicationcanbe easilyextendedto multiple switches(usinga singlePIC16F684,you could control four switches),althoughI suspectthat you will find a certainamountof variationbetweenthe switches, which could leadto someproblems.Tominimizethe chanceof power problemqmake sureyou engageonly one solenoidat a time;if four switchesare activeat the sametime,you shouldsequencethroughthem with somedelaybetweeneachsolenoidactivation.To ensurethere are no power problems,you may want to passthe Vdd voltagesupplythrougha diode and then havea largecapacitor(47 pF to 100pF) provide a temporarypower supplyif a solenoidreducesthe voltaseto zero. accessota

S e c t i o nS e v e n S a m p1 e C l l i c r o c o n t r o l l e n

Applications

155

Experiment55-PC 0peratingStatus Displag

1PrC16F684 I

I4-pin

socket

? 1N914 silicon

diodes

1 1o-LED bargraph

disp lay

10 4700 resistors text )

(see

47 g,F electrolytic caPac].tor DMM NeedLe-nose pIiers

0.01 pF capacitor tYpe )

Soldering

iron

PrototYping

wire

DB-25M solder nector

SoIder Wile-wrap

(any

PCB cup con-

Weldbond adhes ive

One PC peripheralthat hasalwaysfascinatedme is the remotestatusmonitor that providesyou with an alternativeform of feedbackregardingthe operationof your computerin the form of an LCD display,a glowing ball,or a seriesof LEDs. In thisexperiment,Ihave createda simple10-LED operationsdisplaycontrolled by the parallelport that canbe addedto a WindowsPC in just a few hours.It's importantto note that although the PIC MCU sideof the experimentis fairly simpleto build (and is very similarto the other experimentsin thissection),the PC software,despitenol requidnga specialized devicedriver,is fairly sophisticated and plobatrlycannotbe replicatedor modifiedeasily. The circuit (seeFigure7-17)consistsof a PIC16F684connectingto a PC'sparallelport and has

the ability to turn on a singleLED becauseit's poweredby the PC'sparallelport. Poweris providedby sevenof the parallelport's eight output pins.These pins are pulled up intemally by the parallelport and source1 mA of current.which shouldbe sufficientfor runningthe PIC MCU and a singleLED. The remaining I/O pin is used,alongwith the printer strobebit, to latchin a bit of data.When I built my application(see Figure7-18),I useda 470OSIP and a 470Oresistorfor limiting the LED current.You canuseeither this solution or 10individual470f) resistors. The applicationcode(cPerfMon.c)waitsfor eight bits to be sentto it and then XORS the first four bits againstthe secondfour bits,and,if the resultis all bits set,the specifiedLED tums on. *incluale - Display cPerfllon.c /*

Performalrce

Value

from

por! This program conneets to the paralle1 of a Pc and u'i11 receiw€ eight bits of, alata on RA3 (Clock) and RA4 (Data) anal compare the first fou! bits $rith the second antt if they are conpl.ementary, will alisplay the BCD value ort a 10 LED bargraph alispLay. Thia

Figurc 7-17 PerfMon circuit

L56

prograrn

was wlilten

to

r'rork erith

Hardlnrare Not€s: PIC16F581I Runtring at 4 MHz AA3 - Printer Polt CLock RA4 - Printe! Polt Data RC5:RCo - ]Jow 6 Bits of the Display RA2:RA0 - Bits 8:5 of the Display

l , e 3 P I C @I ' l C UE x p e r i m e n t s f o r

the EviI

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RA5 - Bit

9 of

the

DiBplay

llyke prealko 05.oL.22

& WIXTDIS & PWRTEN & ITCLRDTS & -CONFIG(INTIO UNPROTECTr \ & I'NPRC"IECT & BORDIS & IESODIS & FCUDIS),

char char char

BltcounE, = 0t Bitvalue = 0t Bitcotnp

natn( ) t PORTA - 0x3Ft PORTC = 0x3Ft CMCONo = 7, .ANSEI, = 0 t TRISC = 0t rRISA = 0b011000t

/ / Diar,lay

Active

Conrparatsora / / T11r'r off // Turn off aDC // A1l 5 Bi.ta outDuLa // RiA{:8i43 lry)uts

osccoN = osccoN | (1 << {), ( 1 == 1)

rphile

Negative

//

Run Prc ltcu at g !|Itz

/ / l2ooE Eotevet

{ (Bltcounl

= 0r

< {t Bilcount++) Bitcount { Bils // Get First (RA3) t f,or Bit lrhiLe // Igail = (Bitvalue >> 1) + (RA{ * 8)t Bitvalu€ (lRA3)r while // Make Sure Bit ia sish // zof l

for

(

(r

< 8, BiEcount++) // Get Seconal { Bita (RA3 ) t while // wait for Eit = (Bitconp >> 1) + (aA{ * 8)t Bitcoq) (tRA3), while iB trigh // ltak€ gure ait ll rof ,

fo!

Bitcount

{

^ Bilcdll)) t= 0x0F) // No Match, wait fo! Low // wait fo! Hish // wait

( (Bitvalue

t

q'hile(nA3), while ( !RA3) t

) €Lse

//

(BitvaLu€

{

1 Bit

Data oK - r,ight LgD Agpropriale

< 5)

PORTC = 0x3F ^ PORTA = 0n3Ft

// o Eo 50% (1 << Bitvalue), // Eisrh LEDE Off

) etse

if

(Bitval.ue

< 9)

{ PORTC = 0x3Ft PoRTA = 0x3F ^

(1 << (Bitvalu€

-

6))t

) elEe

//

9O%+

{ PORTC = 0x3F, PORTA = 0x1F, /l fi , Bitvalue BttConP ) )

= 0t

//

Reaet valu€a

= 0,

// elihw // Enal cPerf!4on

S e c t i o n5 e v e n

th€

corq)ali€od

cPerfMon.chasa simple,but quite effectivemethodof error detection;if after eightbitE the XOR'd resultis not 0x0F(all bits set),it then waitspastthe next bit andrepeatsthe processwith the next eightbits until the XOR'd resultis 0x0F.With the PC softwaresending data onceeverytenth of a second,it will take up to three-quartersof a secondfor the PIC circuit to becomesynchronizedwith the PC output. Although the PICC Lite compilercodefor the PIC16F684is quite simple,the PC codeto producethe dialogbox shownin Figure7-19andmonitor the amountof main memorythat hasbeenallocatedby the differentapplicationsrunningin the PC will be very complexthe first time you look at it. An important attributeof this applicationis that it doesnot requireany specialprinter devicedrivers.If you have enoughexperiencewith the PC,you will know that mostpdntersrequirespecializeddevicedriversto provide bidirectionalcommunications or evenstatusmonitoring to suspendsendingdatauntil the current buffereddatahasbeenprinted.In this application,I simplyopenthe LPT file deviceand sendthe eightbits of data asonebit of a byte (the other sevenbits are high to ensurethe hardwareis poweredby the parallel port).This is possiblebecausethe parallelport is wired asLoopbackport.As such,it appearsto the basic printer softwareasa "dumb" ASCII printer andwill havedata sentto it at full speed(roughlyone byte every50 ps). The applicationcodeis written to be built under Cygwinand run under GCC,and it consistsof five modulesthat are compiledandlinked together.To debugthe application,I usedDDD, alsorunningunder Cygwin.Theapplicationand filesshouldbe buildable underVisualStudio.Using the open-sourcetoolsfor developmentmeansthat you canreplicatethe application and avoidthe costsof usingVisualC+ + or Visual BASIC. If termslike GNU ProjectGCC C compiler, DDD debugger,and CygwinWindowsinterfaceare Greek to you, don't worry;asyou leam more about programmingPCsand gainunderstandingof how to createand build Windowsapplicationqtheseterms (and tools) will becomemore familiar to you. The basicapplicationitself waswritten in C (for GCC), is calledPerfMon.c,and is listedbelow.This application can accesseither LPT1 or LPT2 or neither, and it rememberswhich onewasactiveby usingthe PC'sregistryfor storingthe lastusedport. I originally wantedthe applicationto displaythe PC'scurrent load,but this turned out to be problematicbecause eachversionof Windowsusesa differentmethodof computingthe currentload.Instead,I displaythe current memoryusage,which can alsobe a usefulload indicatorin a PC if it startsrunningvery slowly.Along with the sourcecode,".rc" files are requiredthat can

S a m p l e C l ' li c r o c o n t r o I I e r

Appl ications

15?

ir.g :.!',i

is i{

ir, i!"{

tn l"1i

i:fga l,p j N

*rt 1,"{ - :

ft? ! :

;.-;

r11 !i'l

LJ ?"J, tA {-} g-."3 !\r

Memorl' Usage: 75% LFT$elect:LPT2 SelectLPT1 elect

ry!!f] i . q Figufe 7-i9 Figufe 7-lB The PerfMon applicotion'scircui.t connectsto and is poweredby a PC'sparalleLport. be found on the PICkit I StarterKit's CD-ROM or at http://www.myke.conr. Thc applicationiconswele createdusingPaintbrush and then convefiedinto ico format.To build the entire applicationand be ableto debugit usingDDD,I used the following statementsin the CygwinX-Windows box: winalr€s %l.rc gcc -mwinalows %1.res -tgdi32

-O coff -o -nno-cyg$rin -l.user32

%1.!es -g -o

%L.exe

eo1.c

Due to the untimelydemiseof my PC on which I normallyuseto createPC and PIC MCU softwarc,I had to breakup the PC and PIC MCU softwaredevelopmenttbr this experimentonto two PCs.Amazingly enough,when the two piecesof softwarewerc brought backtogether,the appllcationworked quite well, althoughoccasionallythe lit LED would changeto an

158

PerfMon operati.ng

unexpectedvalue.Thesolutionto this problemwasto run the PIC MCU at 8 MHz, rather than at the standard 4 MHz, usingthe theory that the incomingdata and changingbit valuesweretoo tast for the 4 MHz device.Thischangeeliminatedthe problcm with the errantLED, and the applicationhasbeenrunningperfectly eversince. Twicein this section,I encounteredsituationswhere the applicationworked well,but neededto be spedup to work perfectly.I want to makesurethat you understandthat in both cases, the problemwasreasonably well definedand the clock doublingwasusedto addresstheseissues. I mentionthis becauseI do not want you to think that by increasingthe clock speed you canfix the problemevely time you havean appli cation that occasionallyruns errantly.Befbre attempting any fix, you shouldhavea theory behindthe cause of the problemand what you expectto gainby the fix. If you don't,chancesare you will not fix the problem or you'll end up with an entirelynew problemrequiring its own fix.

l , a 3 P I C o l ' l C UE x p e r i m e n t s f o n t h e E v i l

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Section

Eight

Introdutrtion to PIE@ MfU Hssemblg LanguageProgramming

PICkit-l

Starter

Kit

Prc16F684

So far in this book,I haveshownyou the highlevel C programminglanguageand how to useit to programa PIC16F684to perform varioustasks.You shouldnow be reasonablycomfortablewith programmingthe chip and comingup with applicationsthat perform useful functions.You shouldalsohaveusedthe simulatorthat is built into MPLAB@IDE to help you verify the operation of your programbeforeyou programa chip or to help you debugyour programonceyou discovered your programdoesn'lwork exactlyasyou thoughtit might.You are now readyfor the next stepon your journey:learningassembly language programming. The computerprogramthat convertsan assernbly languageprograminto the .hexfile andis then programmedinto the PIC@microcontrollerchip is known asan assembler.'fhe assembleris analogousto the compilerprogramthat convertshigh-levellanguage statementsinto a .hexfile.Unlike the PICC@Lite compiler,the PIC MCU assembler(known asMPASM@ assembler)is built into the MPLAB IDE and is loaded automaticallywhenyou insrallMPLAB IDE. Assemblylanguageprogrammingis usuallylooked upon with a greatdeal of trepidation;it is perceivedto be more difficult to learn than a highJevellanguage like C for programmingapplicationsand debugging failingapplications. Another perceptionis that code written in assemblylanguageis more efficientthan codewritten in a highJevellanguage.I would disagree with all of thesestatements. Assemblylanguageprogrammingis not more difficult to learn than a highlevel language; it is merelydifferent. The differenceis in the basicstatementsand in understanding how they are usedto createapplica-

tions.Onceyou are comfortablewriting codein assemyou will find that it is just asmuch mental bly language, work aswriting an applicationin a high-levellanguage. You may find that an assemblylanguageprogram takesmore physicalwork (keying)than a high-level program,but this is due to the increasedgranularityof the assemblylanguageinstructions;eachone performs a muchsmallertaskthan a highlevel languagestatement.Additionally,I would saythat debuggingin assemblylanguageis a lot easierthan in a high-level language, becausethereis muchlessambiguityabout what the programis doing.You probablyappreciate this statementknowingsomeof the strangethingsthat canhappenin C statements. Finally,an applicationthat is poorly written in assemblylanguagewill not outperform an applicationthat is poorly written in a highlevel language. The mostimportantparametersof any programare its readabilityand the efficiencyof the algorithmsthat are usedto implementthe requiredfunctions.If the programcannotbe easilyread,you will haveproblems completingit, gettingit running,and debuggingit. If no thoughtis put into the operationof the application, then it will not run appreciablyfaster.Regardlessof the programminglanguage, theseparametersmust alwaysbe consideredwhen designingan application. An excellentanalogyto the differencesbetweena highJevellanguage(like C) and assemblercanbe illustratedby the commandsneededto explainhow to walk acrossthe room and pick up an object.In a highJevellanguage, the commandstatementswill look somethinglike the following:Turnright, Stepforward six times,Bend over."Assemblylanguage

159

instructionsfor the sametaskwould look like this: "shift weight on left leg, lift right leg two centimeterg move right leg 10 centimetersto the right, lower right leg."Both will get the job done,but the assemblylanguageinstructionswork at a muchlower level. In this introduction,I haveusedthe term instruc,ions to descdbethe assemblylanguagestatements.At its most basiclevel, an instruction is a collection of bits that commandthe processorto carry out a simpletask. For arithmeticoperationqthesebits specifythe task,

€', .{

'".1 lel

whereinput parameter(s)comefrom, and wherethe resultis stored.If multiple arithmeticoperationsare required to carry out a task,then multiple instructions are required.In additionto arithmeticinstructions,a variety of other t)?es of instructions exist that control the operationof the processor, the microcontrollerin which it is built, andspecifywhereand how the codeis to execute.I will explaintheseinstructionsin this section.As I saidpreviously,theseinstructionsperform the sameoperationsperformedby the high-levelstatementEjust in much smallersteps.

w {d

Experiment 57-The asmTemplate.asm File and

0, .tJ ff

Basic Directives

F{

p{

o $"t H E} tu

Beforestartingan assemblylanguageprogram,I generallybeginwith a templatesimilarto the one I introducedyou to earlyin the book for C programming. This template is usedto remind me of the basicinformationrequiredin a programand the basicprogrammingheadinginformationneededto get a basic programrunning.The asmTemplate.asm file that I used for the programspresentedin this book looks like: "asmT€nlrlate title Tet[)Ia!efl E:rplaiD

fll

"c"

tla

//

h

the

Ogeration

Equivalent P1.rt "C"

-

AsselibLy

of

the

Language

Coaling

program.

cofle:

Equivalent

zunction

Eele

Autshor Date

i I

IJIST R=DEC I}{CLUDE',p15f 684. inc"

lJ'

-CO}TFIG -cpD_oFF wDI_oFF

& _BOD OI'F & _FC!'EN_OEF & _IESO-OFF & cP_olr & _!!C!RE_ON & _P!{RTE_ON & & INI,OSCIO

Valiabl€s CBIOCK 0x20 Put Variabl€ Names Here t If Variable lJonger thsr! 1 Bt te, t EIIDC PAGE org aop

" !*{

r

Mainline

160

P.EGE SubroutineE

€nd

Let's go throughthe lines of this file to help you understandthe differentfeaturesof the templatefile. Thiswill alsoserveto introduceyou to someof the information that you will need to carry out assembly languageprogramming. The first line contains the /il/e directive and will place the string in quotes on the first line of every listing pageasa header.Directivesare commandsto the assemblerthat are usedto control the assemblyof the program.Thetitle line that I useconsistsof the name of the file and a brief descriptionof what it does;this helps me find a program with a specific function aswell asidentify the file in which it is contained. The next seriesof lines are commentsand usethe semicolon(;) characterto indicatethat everythingto the right is a commentand can be ignored.Theseare similarto C's doubleslash(i/) comments. They explain the following: .

i

n!

;

r Plrt in

".*B!rtses"

. 0 t Coale

NoP Requiretl

for

The operationof the program AnalogousC code(if appropdate)to explain how the highJevelfunction is to be implemented The author ofthe program and the date that it is written

Debugg€r

The /isr directive is used to specily different assembly andlistingcommandsto the assemblerprogram, which then converts the assemblylanguageprogram into the hex file of instructions to be programmed into the PIC MCU. If you look at the list directive parameters (shownat the end of this section),you will

l , e 3 P I C @l " l C UE x p e ri m e n t s f o n t h e E v i I

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discoverthat thereare quite a few,and many will seem like you shouldusethem.However,the singleparameter that I havespecifiedasa list directivesetsthe defaultnumberbaseto 10 (decimal).(I feel that rhis is the only parameterthat shouldbe specified.)Adding additionallist directiveparameterscan affectthe operation of the final application,how it is programmed, and the difficultyto port the codeto anotherPIC microcontrollerpart number. T}:.einclutledtective loadsan informationfile that addsadditionaldirectivesand instructionsto the programfile.The pic16f684.inc file is found in the folders loadedduringMPLAB IDE installation.Thesefolders are usedto definethe variousregistersand functions of the PIC16F684, relievingyou of the responsibilityof havingto do this (exactlyasthe "#include" directivedid in the C programs).Whenyou are developing rnorecomplexapplications, you may find it useful to put commondefinitionsand codein .incfiles to avoidhavingto key repeatedlyin the sameinformation and providea centralrepositoryof definitions and codesfor all applicationsin your working curent proJect. The _CONFIG directiveis usedto specifythe configurationword bitqjust asthe _config( directivedid in C programming.Like the C version,eachparameter is ANDed togetherto specifywhich bits are resetand which are set.Note that _CONFIG hastwo underscoresandcannotstart in the leftmostcolumn.Also note that whenthe directiveis listedhere in the book, the parametersare generallyprinted on two or three lines,but they shouldall be in the sameline.I have avoidedputtingthis directivein applicationsthat will not actuallybe programmedinto a physicalchip, becausethe double-lineformattingcanmake it difficult to readand key coffectlyinto the experiment's programif it is not necessary.

accomplished and,later in this section,I will note the pointsto take under considerationwhen declaring variables. Next,the resetaddress(address0x000)is specified usingthe drg directive,and the applicationcodestarts after it.The assemblerinitializesits programcounter to zero beforestartingto convertinstructionsinto bit patterns,but it is customaryto specifyzero to ensure the memorylocationstartsat the resetaddress. The nop (pronounced"no-op") stringis actuallyan instruction, which commandsthe processorto do nothing ovel one instructioncycle.The valueof this instruction will be explainedlater in the book;it is a lot more useful than you might imagine.Placingthe nop at the resetaddressis necessary for usingthe MPLAB ICD2 debugger,and,althoughyou may not havean MPLAB ICD2 debugger,it is a goodideato put this simpleprovisionin for whenit is needed(i.e..when the MPLAB ICD2 debuggeris available). Finally,the assemblylanguageprogramcanbe written out in the file.Unlike in C programs,in assembly languageI put subroutinesaJ?er the mainlineprogram. The assemblerreadsthroughthe assemblylanguage sourcefile beforestafiingto createthe .hexfile so that the addressof labels(includingsubroutinelabels)are identifiedand availablewhenthe .hexfile is beingcreated.Thisis differentfrom a C compiler,which doesn't identify subroutineand functionheadersafter they are used.I couldplacesubroutinesat the start of the program,but this would necessitate making the mainline which of the programjump over the subroutines, makesthe programmore difficult to read and follow I realizethat in this assignment, I still havenot givenyou enoughinformationto start programming your own assemblylanguageapplication.In the next you will be able to start programming few experiments, on your own.

T\e CBLOCK andENDC directivesare usedto declareprogramvariables.I will explainhow this is

ExFeriment58-5pecifging ProgramMemorg Fddresses When I am programmingin assemblylanguage,I really don't carewherethe instructionsare beingplacedin the PIC MCU's programmemory.The MPASM assembler that is part of the MPLAB IDE doesa very good job of managingprogrammemoryaddresses and relievesthe programmerof the responsibilityfor calculating the addresses themselves. By following a few simpleconventions, you canwrite assemblylanguage programwithout ever beingconcernedwith the actual addressof an instruction.

S e c t i o nE i g h t P I C o l l C U A s s e m b l y L a n g u a g e P r o g r a m m i n g

161

New Program Counter Addfess (Goto/Call)

DalaBus

PC lncrement Program Memory Read Address

Figufe 8-l

B Element Program Counter Slack

Programcounter

The programcounteris a fairly sophisticated counterthat keepstrack of whichinstructionis to be executednext (seeFigure8-1).In normal operation, after an instructionis readin for decoding,the program counteris incrementedcausingthe addressoutput to point to the next instructionin the program.The valuein the programcountercanbe changedfour different ways: .

. .

.

A new addresscanbe imbeddedin some instruction,and this addresscan be loadedinto the programcounter. The programcountercan be changedalgorithmically by the executingprogram. Cefiain instructionswill incrementthe program counterwhen specificconditionsare encountered. The plogram counter can be updatedvia a last in-first out (LIFO) stack.

As you becomefamiliar with assemblylanguage programming,you will becomecomfortablewith using all four methods,but right now you shouldjust concern yourselfwith changingthe programcounterusinga valuein an instruction. The instructionsthat changethe programcounterto explicitvaluesare the aptly namedgrn andcall instructions, which changeexecutionto the specified addressor invoke the subroutineat the specified address, respectively. Looking at the goto instructionin its mostbasicform, its executioncouldbe summarized asfollows: golo

0x????

t

Ptoglam

count'ef

= 0x0????

The value0x0????is known asan lmrzediate, or lit eral,valueor number.It is part of the programmemory and cannotbe changedduringprogramexecution. When peoplefirst startedprogramming,this valuewas literally a number.Before entry into the computer system,the programwould be written out on a sheetof

L62

paperwith eachaddress, and actualjump addresses would be enteredmanuallyinto the program.Thecode snippetbelow,which togglesan output pin seventimes, is written out with the addresses for eachinstructionto showhow this is done: 0x01234 0x01235 0:.01236 0x01237

Inovlltr' bsf bcf addlw

0x07 0*05, 0x05, oxFF

0 0

i i i i

0x01238

btfss

0x03, 2

i

0r{01239

goto

0x1235

i

Loop 7* PORTA,Pin0=1 PORTA,Pin0=0 subtract 1 fron Loop Counter If Zero Bit Set Skip Over Next Else, R€pea! Bit Pulse

This methodof programmingwasvery tediousand had the potentialfor many errors. As time progressed, the ability to specifycharacter stringsfor specificaddresses wasaddedto assemblers. By placingthe labelin the first columnof the plogram file and endingit with a colon (:), the assemblercould recognizeit asa label and assignthe addressvalueto it.Then,whenthe label wasencounteredagain,the assemblerwould substitutethe addressvaluefor the Iabeland avoidthe needfor the programmerto keep track of the addressmanually.Thelabel alsomakesthe programsubstantiallyeasierto read.Using this ability, the snippetabovebecomes: 0x07 Loop: bsf aaLllw btfss goto

; ; r ;

0 x 0 5 , 0 , 0x05,0 ; oxFF r Ot
Loop 7* - At AaLlless O*OL234 Label halicatiltg llthele to Return Execution P O R T A . P i n 0 = L PORTA,Pin0=0 S.rbtraet 1 frcm ]"oop Counler If Zelo Bit Set Skip Over Next Replace hstruction with Aildresa ( 0x01235 ) $'hen value program assefiibling

Labelsare stringsofASCII alphanumericcharactersthatstartwith ato z,A Io Z,or andcanhave0 to 9 , a t o z , A t o Z , o r f o r a n yo f t h e r e m a i n i ncgh a r a c ters.Labelscan be up to 255charactersin length(the maximumwidth of an MPASM assemblersourcefile) and canoptionallyend in a colon.A labelcan be either on the sameline asan instructionor on its own line.I recommendthat labelsare on their own line and alwaysendedwith a colon (asI havedonewith loop in the previoussnippet).This will help you recognize labelsin the programand not confusethem with instructions,directives,macros,or variableswhenyou first read throughan application. This one simpleability to keep track of the address valuefor a label hasbeenexpandedto the three different methodsshownin the following program:

l,el PfC@ CU Experiments for

the Evil

6enius

,'asrnAddresE title specifying Addrerses"

-

Different

ways

of

Demonslrate the 3 methoalB of speeifying program menory addresses in the PIc rllcu uaing MPASlil assenbl.er. Hardware Noles: PIC16F684 running

at

4 Msz in

SinuLator

Mtake Prealko 04.09.10 LIST R=DEC rNcr,uDE "p15f 584. inc " PAGE ofg nop goto

org

0

Mainline 1st Methott: Jump to i sp€cified Address r

Progranmer

47 r

User

specifieal

t

2nd Method:

r

3!d

Adalress with

ra.be1

MainIi.ne: solo

t+1 Use Relative

AdLIreBs

Loop: goco

Method:

,funq) to

Label

,ratalress

tJoop ,

Plovideal

by MPASM assetnbler

end

Wren you oeate the projectfor an assemblylanguageprogram,you are goingto do it in the sameway you do it in a C languageproject.Betoreyou attemptto link the assembly languagesourcefile to your project usingAdd File,click on "Project"andthen on "Select LanguageTool."Youcanthen select"MPASM Assembler,"followedby "OK" to specifythat the project involvesan assemblylanguageprograminsteadol a C program.PressCtrl+F10to build the assemblylanguage programjust asyou would build a C languageprogram. The first methodinvolvesspecifyinga locationfor executionto jump to, putting in a labelthat is automatically giventhe address, and then executinga goto the label.The new addressis specifiedby the org directive. This directiveforcesall subsequentinstructionsto br: placedin programmemorystartingat this address. Insteadof usingthe org directive,I could haveset the goto addressasa constantvalueor I couldhavejust put the desiredaddressin the instruction(e.9.,goto 47).Although both of thesemethodsseemsimpler, thereis the increasedpotentialfor either an incorrect addressto be enteredinto the goto instructionand for the instructionsat the addressto be incorrect.By using the org directiveto set the start of subsequentinstructions at the label,the goto addresswill alwaysbe the instructionto start at the desiredaddress, and the

instructionsthemselveswill start at the desired address. The needfor explicitlysettingthe startingaddress for a block of instructionsis ra[e.The only situationI can think of wherethis is importantfor the PIC MCU is whenyou are settingthe addressof codethat is used to implementthe interrupt handler.The code addresses shouldbe explicitlyset if the application goesbeyondthe fint codepagein memory.Somepeople like to moveblocksof codeto specificareasof programmemoryto make debuggingsimpler.Because you will not be working with interruptsin the PIC MCU, and becausethe PIC16F684doesnot havemore than one pageof programmemory,thereis no need for explicitlysettingcodeaddresses. The availabilityof the MPLAB IDE with the sourcecodesimulatoreliminatesany advantages of putting blocksof codein specific locations.You will find that i1is fasterto wdte an applicationwith the differentpartsof the codebutted, or concatenated, together. The $ symbolin MPASM assemblerretumsthe addressof the instructionin which it is used.Jumpingto the $ symbolturns the instructioninto an endlessloop. By addingo[ subtfactingconstantvaluesto the $ symbol,goingto addresses relativeto the currentaddress canbe donequickly andeasily,without the bother oI trying to comeup with a meaningful,uniquelabel. The third methodis to usea uniquelabel and goto it. This is generallythe prefered methodof most new programmers.The problemcomeswith trying to come up with uniquelabelsfor complexprograms(the point I madepreviously).TheconventionsI tend to usefor labelsare asfollows: r .

.

There can only be one Loop and one Done label,andthey arein the mainlinc. Within subroutines,Itry to keep to one Loop, one Skip,one Done,and oneEnd labelsuffix, with the labelprelix beingthe nameof the subroutine. Labelsshouldbe reasonably descriptive. Singleletterlabelslike a,n, andso on.makea program more difficult to read than if they describetheir purpose.

If you havebeendoing someresearchabout the PIC MCU, you would havediscoveredthat the programmemorypageslzeis 2,04f1 instructions.Jumping betweenpagesrequiresupdatinga registerknown as PCLATH beforeexecutingthe goto instruction.This is not an issuewhenyou areworkingwith the PIC16 F684,which hasa total of 2,048instructions,but is somethingthat you will haveto undentandif you were working with a PIC MCU, which hasmore than 2,048 instructions.

S e c t i o nE i g h t P I C o l l C U A s s e m b l y L a n g u a g e P r o g r a m m i n g

L63

Experiment59-Loading the I-UHEE and Saving

Its Contents

Unlike a highJevellanguagein which data canflow throughanyvariable,all the data in a PIC MCU assemblylanguageprogramwill alwayspassthrough the working register,which is known as WREG. In other microprocessors, this registeris known asthe accumulatorandis the midwaypoint whendata is beingtransferredfrom one locationto another,aswell asone of the sourcepoints and a possibledestination for mathematicaloperations.Despitethe WREG'S responsibility in assembly language programming. whenyou look at it, only threethingscanbe done with it. . -

. . . .

.

'

The first thing that can be donewith the WREG is to load an eight-bitnumericvalue (known asa literal or immediatevalue)into it. This is typicallydone using the movlw valueinstruction,which storesvalue(or the leastsignificanteightbits of the instruction)directly into the WREG (seeFigure8-2).This instructionexecuteswithout affectingany other resourcesin the PIC MCU. Regbtersare lhe namegivento a group (or a bank) of 128addressable bytes,someof which can be usedas variablesin your applicationand othersof which can accessbuilt-in hardwarefunctionsof the PIC MCU. The variablebytesarecalledfle regisrers. andlhe hardwarecontrolfunctionbytesare known asspeclal registerscanbe movedinto function registers.These the WREG usingthe "movf Register,d" instruction (seeFigure8-3). The leastsevenbits of the mod instructionare the addressof the resisterin the bank that is to be

accessed.The valuein this registeris passedthrougha zerocheckmoduleandthen either passedback to the registeror storedin the WREG This actionhascaused me in the pastto characterizethe movf instructionas havinga primary responsibilityof testingwhetheror not the valueof a registeris equalto zero and a secondaryresponsibilityof loadingWREG with the contentsof the register. I think of the zero testmodule asa dottedAND bus (seeFigure8-4)with eachbit beinga control input to one of the pull-downtransistorswitches,and the bus output beingthe zero bit (calledsimplyZ) of the STATUS register.If any of the bits are set,the line (and the Z bit in the STATUSregisterafter the instructionexecutes)will be low. In the descriptionof the instruction,I noted that the contentsof a registercouldbe optionallystored into WREG or storedbackinto the register.The determinationof wherethe registercontentsgoesis made by the d or destination-bitparameterof the movf instruction.Thedestination-bitparameteris usedby all instructionsthat movethe contentsof a register throughWREG; it will becomeclearerasyou work throughthe section. In somereferences, you will seethat if d is 1,the destinationis the register,and if d is 0, the destination is WREG. In all of my code,and I adamantlysuggest that you follow this convention,the letter/is usedas the registerdestinationand lr is usedasthe WREG destination.In all of the Microchip files includedhere,f is equatedto 1,and w is equatedto 0, so the valuesare the same.But by usingthe letter codes,you shouldsimplify the effort in rememberingwhich numberis used to initiate which action.

"14-Bit lnstruction

Specified

Figure 8-2

Immecl.iate load (movlw) instruction

164

l,A3 PICo llCUExoeninents for

Figure 8-3

Dtrect load (movf) instruction

the EviI

6enius

titl€ Saving

oao Bit7l

Bito ] Figure B-q

DottedAND BusOuiput "1"if all lnputs=: 0

Zero testmodule

,,asmwREG -

IJoatlilg

anal

$REG

This progran dlenonstrates ',ckwnr 'movfn aaal n$ovwf" o9eration WREG to

inEbruction alal bow they ale useal crith move alata withia bhe PIc !,lcu.

Eardlrdare Notes: PIC15F584 runnins

at

{ MHz in

simulato!

Myke Prealko 04.11.17

The final instruction,movwf Register,savesthe contentsof WREG into a register(seeFigure8-5).While the movlw usesliteral addressingto storea specific valuein WREG, the movf and"movwf" usedirect addressingto transferthe contentsof a registerto or from WREG. asmWREGasmdemonstrates the operationof the threeinstructionsdiscussed in this experimentalong with the clrw instruction.Theclrw instructionperforms the sameoperationasthe movlw 0 instructionbut also setsthe zero flag (Z) of the STATUSregister:

LIST R=DEC rNcr,uDE "p15f 684. inc n

PAGE org noD novlw

0

f23

cLrw

t

R6quireiI

i

Load

for

MPLAA 1CD2

WRSG nrith

$REG rrith

Clear/I,oaal

novlw

55

rnovlw

0x55

novLw

b'00110111'

novlw

rU'

FSR

cLrw novf

FSR,

f,

movf,

FSR,

W

t iteral 0

Loaal WREG ldith Decinal IJi.t6ra1 I-oad WREGnitsh Eex I,iteral, Binary loaal WREG lrith !iteral IJoaal WREG wi.th ASCII chalactse! stor€

WREC ilr

clear

WBEG

a Registe!

: _'

set zero Elag Accoraling co cont€nts of Regiater Iroatl VIREG with Register

.:' goEo

FiqureB-5

Directsave

Fini€hed, Okay

Everythins

enal

E x per im ent5U -D e fi n i n gVa ri a b l e s

One of the mostdifficult conceptsfor programmersto understandwhenthey are programmingthe PIC microcontrollerin assemblylanguageis that variables

are not declared.To me.the lerm variabledeclaration meansthat memoryis set asidefor the variablesused in the applicationand is kept separatefrom the application'scode.In additionto specifyingthe memory usedby the variables,often the applicationhex file will includeinitial valuesthat are storedin the variables whenthe hex file is loaded.Whenyou are specifying addresses for variablesin the PIC MCU. that'sall you're doing;you are not settingasidememory,and thereis no ability to initializethe variablesfor specific purposes. In this experiment,Iwill presentyou with a way to specifyvariableaddresses in the PIC MCU that

S e c t i o nE i g h t P I C @l l C U A s s e m b l y L a n g u a g e P r o g r a n m i n g

165

is both efficientand resistantto userdeclaration EITOIS.

The idea that PIC MCU assemblylanguagevariablesare not declaredasin a traditionalsystem,with memoryset asidefor the variablesin the hex file,may be confusing.You might ffy ro specifythe variable addresses manuallyusingan equate(equ) directive. The equdirectiveis usedto associatea labelwith a numericvalue,and it could be usedto declarevariablesin the following manner: j.

equ 0x020 l equ 0x021 k equ 0x022 equ 0x024

t t r

Decla!€

8-Bi!

D€clale Declare

16-Bit Counter Eollowing 8-Bit

Labe13 endlc

-

Defining

variables

This coale demonstrat€s how variablea usiflg aleclareal in PIC l,Icu Assenibler "cb1oek" alirective. Hardware Notes: PIC15F584 running

at

4 MEz in

in

PIc

are the

Simulator

Myke Prealko 04.09.04

counter

IIST R-DEC rp16f684. rNctuDE

t

ine"

variables CBLOCK 0x20

i j, k Datastring:s ENDC

8-Bit variabLe Single rwo 8-Bi! variabLes rtrulli-Byte string variable

i r r

Al"lernalive_i i

EQU 0x21 "ALternative_i

",

sane

ailalress

aa rrjn

PAGE

org

movlw

O trin

47

;

Load

33

r

Loadl "j'

with

Literal

value

with

T,iteral

value

) novlw movwf

22 ; Alternative

Ovenr'rite i

"j'

r

Firisheal,

I,oop

goto

Loop

Foreve!

Adalressj Bttesl

r First variable r Seconal. multi-byte , variabLe i Thirat variabLe

In the previousexample,if lStartAddresslwas 0x020.Labell would be associated with the constant value0x021,Label2with 0x022,and Label3,which followsthe 16-bitvariableLabel2,will havethe value 0x024.Thesevaluesare assignedto the labelsat assembly,or build,time without requiringany effort on the part of the programmer-includingif you were to add or deletesomevaluesbetweenbuilds. To demonstratethe cblockdirectiveaswell asthe equ directivemethodsof declaringvariablesin PIC MCU assemblylanguageprograms,I createdasmDeclare.asm. In this program,I havecreatedthreesingle byte vadables(the latter two on the sameline and separatedby a comma)and a multibytevariable.Theequ

t66

"asnDeclare title MCU Assenbler"

Coulltels

The biggestproblemwith this methodshouldbe immediatelyobvious-it's a lot of work! Not only is it work to write out eachvariableand makesureit hasa uniqueaddress, but insertingor deletingvariables requiresupdatingaddresses to make suretherearen't any holes.Another issueis how multibytevariablesare declaredand maintained.In the exampledeclaration of the four variablesabove,it is easyto forget that k is 16 bits and takesup two bytes,and the next variablein sequencemuststart at an addresstwo higherthan the l6-bit variable. In the mid-1990s, when I fint startedprogramming the PIC MCU, this wasthe acceptedmethodof declaring PIC MCU assemblylanguagevariables.It certainly wasn'tperfectand it wasresponsiblefor a lot of difficult-tolocate errors.A few yearsago,Microchipadded the cblock dtectr\e (with the endcdirectiveending)to MPASM assemblerto make it easierto create sequences of numbersfor a seriesof labels.Theformat for the cblockdirectivefor declaringvariablesis: cblock lstart Label1 Label.2 Size in

declared variable is at the same address as one of the cblock-declared variables O and, when written to, will overwrite the cblock-declared variable j.

enal

The body statementsof the programare initialization statementsfor the variables,and the valuesthat get storedin them canbe displayedin the Watchwindow of the simulator.Theseare the samestatements that werepresentedin the previousexperiment,but appliedto variables. you will disWhen you simulateasmDeclare.asm, coverthat the vafiablej is overwrittenwhenAlternative_iis written to.The reasonfor this is simple:Both variablesare at the sameaddressand a wdte to one variablewill affectthe other.Thiswould not be the caseif variablesweretruly declaredin PIC MCU assemblylanguage. An obviousconclusionto this experimentis that you shouldnevermix cblock declaredvariableswith equ declaredvariables.I would go further and saythat variablesshouldbe declared usingcblockonly.

l , e 3 P I C @l ' l ( U E x o e r i m e n t s f o r

the Evil

Genius

Along with declaringvariables,the cblockdirective canbe usedfor declaringdatastructuresand for enumeratinglabelsfor applicationssuchasState Machines.Usingcblockdefinedlabelvaluesin these caseswill allow simplercodingaswell aseliminate

much of the maintenancerequiredof individualequ directivedefinedlabels.The dynamicnatureof the cblockdirective(it is updatedeverybuild cycle)makes it idealfor useanywherethat changingnuneric label valuesis reouired.

61-Bitt-uiselnstructionE Experiment

Bitwisebooleanoperatorsare the mostbasicdata processinginstructionsthat canbe performedin a processor.Theseinstructionscanbe built out of standard gatesquite easilyand do not havethe sameoperational issuesthat are presentin additionand subtracTheseinstructionspedorm the basic tion instructions. Iogicfunctionsover all eightbits of two parameters, onebeingWREG and the other beinga parameter specifiedin the instruction. Two-parameterbitwiseinstruction(i.e.,AND, OR, and XOR) executionfor direct addressing(thosethat end in wf) is shownin Figure8-6.In this case,the contentsof a registerare operatedon with the contentsof WREG usingone of the threeBooleanoperations.The destinationof the resultcanbe either in the WREG or backin the registerusingthe d parameterof the instruction.The ability to return the valueto the regis-

but, asI will showin ter may seemto be unnecessary, handy. it can be extremely the next two sections, The dataflow of bitwiseBooleanoperationsthat canbe performedagainstthe contentsof WREG and a Iiteral value(causingthe instructionsto end in lw) are shownin Figure8-7.Theseinstructionsbehavesimilarly to thosewith a direct addressexceptthat they haveonly one possibledestination,WREG.Inboth cases, if the resultof the operationis zero,then the zero (Z) STATUSbit is set,otherwiseit is reset. bitwiseinstruction, Thereis alsoa single-parameter calledcomf Register,d. This instructioncomplements (i.e.,doesnot negate)eachbit of the specifiedregister andreturnsthe resultin eitherWREG or the source register.If you wantedto complementthe contentsof the WREG, you could usethe followingliteral XOR instruction: xorlw

oxEE

t

complement

each

bit

of

WREG

the operdemonstrates In this case,asmBitwise.asm lanMCU assembly ation of the differentbitwisePIC guageinstructions.

14-Bitlnstruction

Figure 8-6

Two-parameter direcr

Figure B-7

literal Two-parameter

S e c t i o nE i g h t P I C @1 1 C UA s s e n b l y L a n g u a g e P r o g r a m m i n g

167

'asmBitrdise litle Inatructi.ons"

u)

-

Demonstrale

Bitwise

r.f

r t t i

^ or.FF i=t = 0x3B ^ oxFr = o:rc{ 'IREG ltnchangeal

r t t , t t t t t

=wREc ^ i = oxt.B ^ oxc4 = 0t<3F WREG= WREG ^ i = oxFE ^ 0x3F = 0xc4 i =WREG ^ = 0 x 3 B ' 0xc4 = O*FB

r

Finished,

This Dlogram al€nonBtrat€s the oD€ratioD of !b€ Bitwia€ instructions on $rREc anal a Fi16 Regisler incluiling !h€ oDeration of the zeto Status F1ag.

xorwf

t.f

Ilaralware No!€a: PIC15F6g4 ru$ing

xorwf

i,w

,ror$tf

i,t

goto

S

al

4 MHz ia

Simrlator

Myk€ Pleilho 04. LL.!7

L.

n .-l .lJ

U |ill

r.l {J

gt

k

l-t

s

IJIST R=DEC INCIITDE n915f 58{.incrl CBI.OCK 0x20

Declaration

PAGE org nop

0

novlw mor rf movllc movDrf

0x3F i 0xF3 j

movhr analwf

L23 i, w

rlovlw anahflf

L23 i, t

.rl

'd j,w

1d

4

r

Requiredl

r

hltialize

fo!

UPIllB

Ev€rything

Okay

enal

ENDC

(.,

.r{

VallaltL€

t

i

ICD2

Varl.abLes

r , i r t

Initialize WREG = = = Z=0,

, r i t i

Initialize WREG i = = W R E G & i = 0t<7B & 0x0F = 0x3B Z = O, WREG Uachangeal

r t t t

wREc=wREclj = 0x7B + 0r.E3 = oxFB j lrnchaDgeal Z=O,

WREG WREG & i 0!r7B & 0:.3F 0x3B i Unchang€al

Beforegoingon,I would like you to considerthe threeXORS at the end of the program.I didn't explicitly summarizewhat they are doing. However, if you were to look through them, you would discoverthat they not only demonstratethe operation of the xorff statementwith differentoptionqthey alsoare a code snippet that you should keep handy.The following three instructions swap the contents of WREG with the contentsof a register,and they are much more efficient than coming up with the equivalent assemblylanguagestatementsfor the traditionalregisterswap: //

EltaD

"i 'r aud

i = i; J = i;

Whenyou perform traditionalhighlevel programming,therearen't a lot of opportunitiesto usethe bitwise instructions,but in assemblylanguageprogramming,they are critical to your ability to create very efficient applications.

!!

Experiment 5a-Fddition Instrutrtions

{\

back into either the WREG or a sourcefile register. What makes this instruction different from the bitwise instructionsis the productionof two carryvaluesthat can be usedastest valuesfor controllins the execution path of the program.

t'l

du "p4 t . fit !.,.{ f,.d f -'l

The PIC microcontroller's addition instructions are very similarto the bitwiseinstructionsof the previous experiment:Data is set up in the WREG it is arithmeticallycombinedin someway,and the resultis put

168

T\e carry and digil carry STATUS register bits are just as normallyreferredto asC and DC, respectively, the zero bit is referred to as Z. Theseabbreviationsare usedin PIC MCU assemblylanguageprogramming to indicatethesebits and shouldneverbe usedfor variableor labelnames After passingthe s]omto the Operation Result,the carrybit of the additionoperationis savedasbit 0 of

l , e 3 p I C o l l C L JE x p e n i m e n t s f o n t h e E v i l

6enius

the STATUS register and is usedto indicate if the resultof the additionoperationis greaterthan 0x0FR This bit is often usedasan indicatorfor 16-bit(and greater)operationsto indicatethe resultsthat addition to lower byteshason the higherbytes. The digit carry bit (bit 1 of the STATUS register) performs a similar operation but for the least significantfour bits of the result.Digit carry is not the same asbit 4 of the sum.Thedigit carry is the carryresultof bit 3 of the sum;it is difficult to illustratethis in diagrams(seeFigure8-8),but its operationcan be illustrated clearlyusinga testprogramlike asmAdd.asm. When you simulateasmAdd.asm, I suggestthat you displaythe contentsof the STATUSregister(and WREG) in a Watchwindow.The contentsof the STATUS registershouldalwaysbe displayedasbinary rather than the defaulthex.I realizethat the stateof the carry,digit carry,and zero bits, along with the contentsof WREG are displayedat the bottom of the MPLAB IDE desktop,but still I find it usefulto have them in the sameWatchwindow asthe other registers andvariablesusedin the application. "aamAaLl tille Ins!ruc!Lons" Thia Drogram the aatalition oDeration of Statsua Elags.

Adtlitsion

alenonstlates tshe operaEion of iEst'rucliona inclualing the tlre Zero, Carry arral Digit Calry

Haralware Notea: PIC15F58{ running

al

4 !,ItIz in

Slmulalor

Mtzke Plealko 04.09 .27 LIST R=DEC INCLI'DE'rD16f 684. inctr CBLOCK 0x20

,

Variabl€

Declaralion

ENDC PACiE or9

fiovLw {rovwf

0

0x0F

r

Requireal

r

Iniliallze

for

MPLAB ICD2

variabLes

0xF0

clrvt

i ,

cLear WREG z = L

i , ; i

WREG = = = Z = O,

WREG + i 0 + 0r<0F 0x0F C = 0, DC =

t i i ,

VIREG = = = z = O,

WREG + i 0x0F + 0t0E 0x1E C = 0, Dc =

t

rlt

ICREG = WREG

0 x L E + 0x0F O*2D

9"i:

t?q w

t i t t

WREG=WA.EG+k = 0tr2D + 0xF0 = 0x( 1) 1D = 0x1D

, i r , ,

WREG= = = = Z = !,

;

Eini6heat,

f l

&:i

goto

$

I{BEG + 0xE3 0x1D + 0xE3 0 x ( 1 )0 0 0x00 C = 1, DC = 1 Everyuhing

tr-h Okay

entl

f\3

The first addition operation (zero plus 0x0F) has a nonzeroresult,and the threeSTATUSflagsindicating the resultof an additioninstructionare all reset.I then add 0x0F to the value in WREG again and, as expected,the resultis 0x1E.Thissecondadditionhasa lower four-bit sum and a (digit) carry to the next larger four bits,so the DC STATUSbit is set.I shouldpoint out that coincidentallybit 4 of the sumis alsoset. To prove that bit 4 being set is a coincidence,I repeatedthe additionof 0x00Fto 0x1Ein the WREG In this case,the sumis 0x2D,but you will seethat the digit carryflag is still set eventhoughbit 4 of the sumis reset.The digit carry can be confounding and difficult to predictits value.For your initial PIC MCU assembly programming,I suggestthat you ignoreit andjust focus on the carry and zero STATUS register bits for retuming addition instruction information. The final addition operations causethe sum in WREG to be greater than OXFRcausingthe carry flag to be set.Note that up to theseinstructions,the carry flag is reset becausethe results are alwayslessthan 0xFEThe first additionproducesa result of 0x11D,and the mostsignificantbit is usedasthe carry This canbe donebecause, unlike the digit carry,no other bits are part of the final sum. The lastadditionvaluewaschosento producea zero result,but whenyou simulatethe program,you will notice that all three STATUS register bits will be set.Not only is the carrybit setbecausethe sumis greaterthan 0x0100,but the zero bit is set (becausethe savedeightbits are all reset)azd the digit carry bit is set (becausethe sumof the leastsignificantfour bits are greaterthan Ox00F).This may not seemimportant for addition,but this resultwill be very importantin caffyingout subtraction,asI will discussin the next exDerrment.

5 e c t i o nE i g h t P I C @n C U A s s e m b l y L a n g u a g e P r o g r a m m i ng

L69

: *

b,

&r" 9.3 '

rr h

6*d trn r*

q.{ tr!

q rA

Experiment63-HddLibs: Strange5imulator FleEults WREG = I'|REG + i

140 + 140 2ao b , ( 1 )0 0 0 1 1 0 0 0 , b,000L1000, 0x18 24

Before goingon, I want to showyou how the simulator will seeminglyfail and producean incorrectresultfor an arithmeticoperation.Thecodefor this experiment wastakenfrom a high schoolquiz.Thebasecodewas givenin the test,and the studentswereaskedto verify what it did usingthe MPLAB IDE simulator.When the studentsenteredthe codethe simulatedresultwas totally unexpected. I would like to askyou to load the followingcode, asmAdd2.asm.into the MPLAB IDE and enablethe simulator. titl"e

"a€'lAaLl

2 -

Simulatot

This program Shows how the Sinnrfator apparently alispLay t'he wrong re€u1t atldition o!'eration. llarflware Notes: PIC16F584 running

can to an

at

4 MEz in

Simulator

r

variable

DecLaratiolr

r

Requir€al

for

r

Inilial.ize

Myke Pletlko 04.1,2.09 LIST R=DEC INCLUDE "p16f,584.i!rc" CBLOCK 0x20 ENDC PAGE org nop movlw movwf,

1zo

0

140 i

ltPLAr

Variabl€

ICD2

After buildingthe code,single-stepthroughthe codeto the addwfinstruction.After executingit, the simulatorstopswith a valueof 0xB5 in WREG (my result),but asshownin the code'scomments,the expectedresultsare 0x018or 24 (decimal). What happened?The answeris no instructionis givenafter the addwfwherethe simulatorcan stopat, and thereforeit executesa numberof instructionsin the simulatedchip programmemorybeforestopping. You canbetter seewhat is happeningby clickingon "View" and then "Program on Memory."The instructionsfor the start of the applicationmatchthe asmAdd 2.asmcode,but the instructionsafterwardare all "addlw 0xf!" and so it appearsthat the simulalorhas executedfor 256(0x100)instructionsafter executing the "addwf I, w" instructionbeforestopping. This is actuallya good exampleof how smallprogramswork in a PIC MCU Even thoughthey take up a smallfractionof the programmemoryavailablein the chip,the programmemoryis still presentand they executeasaddlw0xFFinstructions. To avoidthis issue,Itend to usean endlessloop (goto $) althoughmany otherslike to usea nop.Any instructionwill do.I like the endlessloop asit will keepthe simulatorfrom executingadditionalinstructions,which canchangethe contentsof registersor bit flags.These instructionswill give the simulatoran instructionto stopat rather than havingthe ambiguous situationof this application. I realizethat I haveindicatedthe needfor the instructionwhich endsthe application,but the kids in the high schoolcourseweretold this aswell.It's easy to forget unlessyou haveto work throughit and try to understandwhat is happening,asI havein this experiment.

l , E 3 P I C o l l C l JE x p e r i m e n t s f o r

the Evi I

6enius

ff

Experiment6l-l-5ubtracti on InstructionE A _ B = A +

X

U

( - B )

tv but when working with digital logic, this is not quite true. To negate a binary value (convert it to its complement in base2), you complementthe bits and increment the result:

._{

- g = ( B ^ o x F F ) + 1

Subtractionin PIC MCU assemblylanguagewill probably be the most consistentlydifficult thing you will have to work with. This is due to the nonintuitive way the instructions execute.You'll find that the data is handled backwardsand the carry and digit carry flags will not work asyou would expect.Many PIC MCU assemblerprogrammerstry to avoid working with the subtractinstructionsall together,insteadcreatingsimilar capabilitieswith other instructionsIn this experiment,I will showyou how the PIC MCU subtraction instructionscanbe usedin differentsituations. The first point to rememberabout the subtract instructions is that they alwaysadd the negative contentsof WREG to the instruction'sparameter.The actual subtractingcircuitry is really a modification to the addition circuitry with either the negative value of WREG or the unchangedvalueaddedto the second parameter(seeFigure8-8). In gradeschool,you wereprobablytold that subtractionwasthe sameasaddingthe negative,that is:

When this 2's complementvalueis addedto the second parameter,the eight-bit result is the sameasyou would expectfor subtraction (again remembering that it is WREG taken awayftom the parameter).But the carry (C) and digit carry (DC) STAIUS flags are not what you might expect.To simplify, don't worry about DC, but focus on predicting the state of the zero and carryflagsbasedon differentvalues(seeTable8-1). The carry flag after subtraction is often referred to as the negativeborrow flag,because, whenit is reset,the subtractionresultis negativeand a one shouldbe borrowedfrom the next highestbyte. Further confusingthe operationof subtractionis the apparent reversal of the instruction from what seemsintuitive. In other processorassemblylanguages, whenyou seesomeinstructionslike the following: nov Eub

Acc, Velue]. Loaal Accunulator r Acc, va1u62 Subtract Value2 ;

with

the

Subtractenal

*;l

i ! {*

ry t*

n

t*"

o

f,rom Va].uel

Ft

you expectit to executelike this: Acc = Valuel-Value2;

Direct Valle

e :

H

But, in PIC MCU assemblylanguage, the analogous instructions:

:

l

I,\

Lite€l Value

movf,

va1ue1, w loail Accrurulalor lritb lhe Subtractor i subwf value2, !t Perform the Sublraclion O9elalion i

Add/Sub

Table8-1. Zerc and EarrusTFTU5Bits Ffte. subtraction

l{

t , ,r+

OBeration

WBEG Parameter Flesullsof Parcmeter+ |-WEEGI

Figure B-B

Subtraction

W R E G : 0 x F F ( - 1 ) , C= 0 , 2 = 0

0x02

0x01

0x02

0x02

WREG=0,C-1,2-1

0x02

0x03

WREG:0x01,C:1,2:0

S e c t i o nE i g h t P I C o t l C U A s s e m b1 y L a n g u a g e P n o g n a m m i n S

H V'

L77-

producethe actualoperation:

cBIrocK

t variable

0x20

DoclaratLon

ElIDC

WREG=Value2-Value1; PAGE

{0 L; L' .Fl

v rl

This can be both confusing and frustrating when you are new to PIC MCU assemblylanguageprogramming.There are a number of things that you can do to make the operations simpler.The first is to add the negative.Instead of trying to figure out how to use the sublw (subtract WREG from literal), you can add the negative.That is: -47

aalill$

H

t)

i

wREc = I|REG -

0 nop

movwf novf, subrf

t Requirotl 0x01 i 0x02 J i, j,

\r rd

4?

Another method is to only use the subtraction instruction the sameway,all the time. You could start with the basicsubtractionstatement: novf aulntrf

A = l l - c

j , w i,w

H and you can convert it to PIC MCU assemblylanguageusingthe instructionsequence:

o .F{

P

d H i l

*{

3

?n I

t

s

c, w B, w a

novf sulrff

In this sequence,if B or C is a literal value,then insert sublw and movlw in their placeq respectively.If B is the sameasA, the last insftuction (mov*f) could be eliminatedand the subwfinstructionchangedto subwf B, f. Finally,the methodI recommendis to add the subtract instructions to your application asyou think they will work, but write out what you expectthe operations to do asI havein asmsubtract.asm. Then,when you are simulating the application,you can compare the actualresults(both in WREG or the file register and in the STATUS register) to the expectedvalues you marked in the application and on which you have basedthe application'soperation. tra$rlsubtracl title InBtructsi.onEn

$ 6 .rl l{

ql P{

X 14

hitlalize

i,w i, !r

-

ale th€

a bi! rBore atlalition

j - i r Stsarts with rWREC=j-l{REc = O,iO2 + (WREG ^ orcF) , = 0x02 + (0x01 ^ oxF!') r = O'tO2 + oxEE+ 1 t = 0x02 + oxFF t = 0x(1) 01 , t WREG = 0x01, C = 1, DC = L,

!&rke P!€flko 0{.11.19 LIST R=DEC INCIjIDE trD16f 58{. inc "

Lt2

at

{

+ 1 + 1

Z = O

r N € x t i - j tVlRECl=i-WREG = 0x01 + (wREc ^ o:
tNo!r, i -i TVIREO=i-WREG = 0:101 + (WREG ^ oxFF) + 1 = 0x01 + (0x01 ^ orlFF) + 1 = 0!101 + o:.FE + 1

ovlw aub1rd

0x01 0x10

6ub1tt

0x10 0x0

r WREGE 0x10 - 0x01 r WREG- 0x10 - $REe = 0x10 + (WREG^ onFF) + 1 r = 0x10 + (0x01 ^ oxFa) + 1 ; = 0x10 + oraFE + 1 t = 0x10 + otcF t = 0x(1) 0F ; ; WBEG= 0x0F, C = 1, DC = O, z - O , WREG = 0 x 0 1 r I{REG = 0x01 0x01 0x01 0x01 0x01 0xF1

+ + + +

0x10 WREG (WREG ^ oxFF) + 1 (0x10 ^ oxFF) +1 oxEF+ 1 0xF0

waEC = 0:€1, C = 0, DC = L, z = 0 goto

$

;

AlniEhett,

Ev6rylhing

Okay

€ntl

RBIEMBER, tshe Negatlv€ Contetts of, WREG are Add€il lo thg instsruetsion algl'ment, Halt\rare Notses: PIC15F664 runninq

ICD2

= 0x01 + 0:{rT , = 0x(1) 00 r t WREG= 0x00, C - 1, DC = a, Z = 0

Subtract

fhe Subtract Instsructions codE)lex in operalion tha! inalructions:

UPLAI

varj.6b1€s

, WREG= otFF. trovf aubwf movwf

rn

11

t

for

MHz itt

SlfiuLator

Hopefully,I have not made the two subtract instructions scarier than they actually are.You might want to createan applicationlike asmSubtract.asm and put in different values.But the best way to learn the subtract instructions is to use them in your own application and confirm they are working by using the simulator. By doing this you will be farniliarizing yourself with the subtraction instructions work and becoming more proficient with the MPLAB IDE simulator.

l , P 3 P I C @l l C U E x p e r i m e n t s f o n t h e E v i l

Genius

Experiment 65-Bank Fddressing Prekir* 1

So far, you havebeenintroducedto how programsare structured,the MicrochipPIC MCU includefile,execution changes(gotos),register/variable declaration, and dataprocessing. By all rights,you shouldbe ready to start creatingcodefor actualhardwareapplications. Unfortunately,the next topicsdon't build on each other aseasilyasthe previousonesdid, and to be able to codesoftwareto run in a physicalchip you needthe informationin all the topics.To try and breakthis deadlock,I want to skip to what is normallyone of the lasttopics,the PIC microcontrollerregisterbanks,and showyou hoq with the instructionsand information you havebeengivenso far, you cancreateyour own applications. Earlier in the section.Isaidthat there are sevenbits set asidein eachinstructionto accesses a register.They are the register'saddress.This meansthat eachinstruction canaccessup to 128differentbyte-sizeregisters. This isn't a bad amountof memory but the PIC MCU designerswantedto be able to providemore,so they d.ecrded Io bank the registersand provideup to four banksin the midrangePIC MCUs.Eachbank consists of a numberof commonand uniquespecialfunction registers(processorand hardwarecontrol and interfaceregisters)and generalpurpose,or file,registers. Theseregistersmay or may not be shadowedbetween the PIC MCU's registerbanks,and therewill always be the needto accessregistersin more than one bank in your application.Theconceptof registerbankscan be difficult to understand,but you mustif you are to createPIC MCU applications. The mostvivid exampleI cangive of the PIC MCU's banksis a spicerack;whenI wasa kid, a friend'smom had a spicerack her husbandhad made her.Thisrack stoodon her kitchencounterand was ableto hold manyspicebottles.It wasbuilt to hold the spiceson eithersideand wasmountedon a small turntable.When a particularspicewasrequired,the rack would be tumed to exposethe sidethat held that bottle of spice.Thisarangementseemedto work well,

althoughthe rack had to be turned repeatedlyduring the preparationof a mealbecausetherewasno way to prearrangethe bottlesso that a singledishwould use spicesfrom only one sideof the rack. The banksol registersin the PIC MCU are very similarin conceptto this spicerack (seeFigure8-9). The differentregistersare arrangedin sucha way asto providemostof the usefulfunctionson one bank (one sideof the spicerack),but you may haveto changethe sidethat that is exposedduringan application.The control for which sideis exposed(or executefrom) is the RPObit (bit 5) of the STATUSregister.When this bit is reset,bank 0 is accessible;when this bank is set, bank 1 is accessible. As can be seenin Figure8-9,STATUSand a number of other registerscan be accessed from eitherbank (like therewasa hole cut in the spicerack so a bottle couldbe reachedfrom either side).For transferring data betweenthe two banks,the file registersin the addressrangeof 0x70to 0x7Fare commonbetween the two banks.Along with thesecorzrnon, or shadowed,registers, a numberof other registersexist (both specialfunctionandfile registers)that are uniqueto eachbank.For most of your initial applications, you will be ableto run almostexclusivelyout of bank 0. The only registersyou will haveto accessare the TRIS registersand the ANSEL registers. Changingthe currentbank canbe accomplished by usingthe followingcode: novf iontrf movwf

STATUS, w 1 << 5 r sTATus

Set

RPo - Change

to

Bank

1

RPO=0 RP1

ShadedRegisters AreShared BetweenBanks Figure8-S

PIC16F684banks

S e c t i o nE i g h t P I C @t l C U A s s e m b l y L a n g u a g e P r o g r a m m i n g

L73

anal novf, analwf firovwf

STATUS, w oxrF ^ (1 << 5)

r ,

R€set RPo - Change to Bank 0

sTArus

T\e leJtshijl operaror(<<) in the statements above,shifts1 to the left by the specifiednumberof bits.I usethis methodof specifyingbit constantsrather than usingdecimal,hex,or binary constantsbecauseit is very difficult to screwup.With constantvalues,you mustalwaysrememberwhich digit,column,or value eachbit valuehas.By usingthe left shift operator, rememberingthesevaluesis not required.When setting or resettingindividualbits,I recommendusingthis format for constantvalues,becauseit avoidsthe need to verity the valueusedfor the specificbit. When you are changingSTATUSregisterbits,you cannottake advantageof the ability of the andwf and iorwf instructionsto changeall the bits of the STATUS registerusingcodesuchasthefollowing: movlw iorwf

1 << 5 STATUS.

; f

Set

RPo -

Change

to

Bank

TRISA.

titLe

,,asnFlash.Naala

-

This Plogram FlaEhe6 betvreen AA4 (Positiv€) appro*imatsely 2x De! any aalvanceal control Ilaralwale Not€s: PIC15F684 running clock Intelna1 Reset is B,A4 - LED Posicive BjAs - LED Negative

at

prc15F584

Elashing

rJEDn

tshe PICKit D0 I,ED anal R.A5 (negative) secondt without u€ing instructions.

4 MHz Using

at

hterlral

lhe

usedl

llyke Predko 0{.11.19 LIST R=DEC INCIUDE trp15f584.inc" FCMEN OFF & _IESO_OFF & _BOD_OF!' & -CONFIG ,CPD OFF & CP OEE & _!{CIJRE_ON & _PWRTE_ON & WDT Or'F & IN:IOSCIO

w

"Message[302] you would get the assemblermessage C: {Filename/LineNumber}:Registerin operandnot in bank 0.Ensurethat bankbits are correct."because the addressspecifiedin the PIC MCU includefile givesTRISA the address0x85.Thenumber0x85is 133 decimaland useseightbits,not the seventhat is requiredfor addressingthe contentsof the bank. The simplesolutionto this problemwould be to changethe TRISA definition to 0x05,which seems correctbecausethe TRISA registeris at address0x05 in bank 1.But I am goingto suggestthat the label is Ieft asis and havethe constantvalueXORed with 0x80,which will resetbit 7 of the address.The first is the indexregisterusesit to differentiatebetweenregis-

Llq

With the informationyou now have,you cancreate a completePIC MCU applicationand to demonstrate this.I createdasmFlashNada.asm, which will flash "D0" in a PICKiITM1 starterkit:

1

The STATUSregister'sC, DC, and Z bits are affectedby bitwiseand arithmeticoperations,so the PIC MCU designersdecidedto not allow statements that canchangetheseflagsto alsowrite to the STATUS registersimultaneously. The reasonis simple: After the instruction.it is difficult to definewhich bit is valid.By forcingthe userto readfrom and write to the STATUSregisterexplicitly,thereis no ambiguityin determiningwhich valuefor which bit is to be usedby the applicationcode. After changingto bank 1,if you were to accessregistersin that bank directlyasyou would in bank 0, say: movf

tersin bank 0 and bank 1 (it is an eight-bitvalueand can accesseachbyte of the two 128-bytebanks).This canbe usedin your applicationsto effectivelyoptimize somecodefunctionsaswell asto provide arraysin both banksthat canbe accessed easily.Thesecondreasonis that XORing everyeight-bitaddresswhile executingin bank 1 will serveasa reminderto you to makesurethe correctbank is executing.If the message comesup and you are in bank 0, then you shouldlook over your codeand add the corect bank switchcommands.Similarly,if you are accessing a bank 0 register while in bank 1,by XORing the addresswith 0x80,you will get a warningmessagestatingthat bit 7 is set (tellingyou that you are accessing a bank 0 register while executingin bank 1).

Variables CBITOCK 0r.2 0 Dlay:2 EIIDC ,

r

PAGE Mainline org

0

no9

r For

c]rf,

PORTA

movnf novf ior10 nov$rf clrf

CMCONo STATUS, w 1 << 5 STATUS ANSEL ^ 0x80

r Initsialize r Tuln

l,e3 PIColl(U Exoeriments fon the EviI

ICD Debug

off

I/O

Bits

to

Coq)araCora

(Bit 5) r s€t the RPo Bit in Page 1 r to Execut€ r Al1

Bits

are

6enius

Disital

ttlovlw Output s movlrf novf anallw novwf

b'001-111'

RA4/RAs

TRISA ^ 0x80 STATUS, vt oxFF ^ (1 << STATUS

Clear

IJooP: clrf clrf Dlayloop: movld

Dlay Dlay 1

Dlay, f nt sTArus, | << 2 PCL, f

goto nop

DlayIJooD

nop noD novlw Bubrdf movf analLv aatallrf goto trop

RPo

Decrenent IJoop

the

Inside

Zelo Elag Set? check Bit 2 AaLl to the Program Counte! Zero, loop Arounfl space change in Address due Zero Flag Being Set

1 Dlay + 1, f sTATUg. w ! << 2 PCIJ, f DlaylJoolt

Decremenl loop

the

Check

Zero

for

Oulgiale

r Space change in aaldress i dlu€ i Z e r o Flag Being Set

nop nop movlw xorwf

DiqitaL

Return llere aft'el. D0 Toggle sigh 8 Bits for Delay Irow 8 Bits for DeLay

+ 1

subvrf movf andlnr adarlrf

are

L << 4 PoRTA, f

Tossle

i

RA4 (D0)

Repea!

€nd

Thereare really no new instructionsin this application, at leastnone that you haven'tbeenshownprevi-

ously.Thereis howeverone pafi of the applicationthat will requirea bit of instruction.This is the ideaof conditionaljumps.No if, for, or while statementsexistin PIC MCU assemblylanguage, and so,to implement jumps that are conditionalto the statusof the previous instruction,I take advantageof one of the mostwonderful featuresof the PIC MCU, its ability to access any registerdirectlyin the applicationcode.Toimplement the conditionaljump,I add the STATUSregister'szero bit (bit 2) to the lower four bits of the programcounter(the PCL register).The codeworks asfollows: = Program Program Counter ( S T A T U S& ( 1 < < 2 ) )

Counter

+ 1 +

If the zero flag is reset(the previousinstructiondid not resultin a zero),this codewill simplycontinueon at the next instruction.If the zero flag is set,then the programcounterwill be loadedwith the cuffent instructionplus four (becausebit 2 hasa constant valueof 4). I addedthe three nops,or no-operation, instructionsto spaceout the codeand make sureexecution,when the zero flag of the STATUSregisteris set,takesplaceat the correctaddress. In the following experiments,Iwill showhow conditionalexecutionis implementedin a more conventionalmanner. Tiicks like the conditionaljump usingdata movement and arithmeticoperatorsare one of the reasons why I really like working with the PIC MCU The PIC MCU, more than any other smallprocessorarchitecture that I know hasbeendesignedwith the flexibility requiredto perfom someamazingtricks that will help makeyour applicationsmore efficientand help you to think throughproblemsin differentways.

Experiment 56-Bit InEtructions

In the previousexperiment,I discussed the conceptof banksand the ability of the assemblylanguageprogramsto accessany registerdirectly.I alsoshowed

how bankswerechangedand how bank 1 registers (including,mostimportantly,the TRIS registers)were addressed in an instructionso no messagewasproducedby the assembler. Finally,the operationand accessof the STATUSregisterwaspresented,and then a methodof changingthe programcounterconditionallywaspresented.In short,I dumpeda lot of new informationon you. The bit set (bsf) and bit reset(bcf) instructionspresentedin this experimentare somewhatlessdemanding but will be usedasmuch in your assembly

S e c t i o nE i g h t P I C @l l C l J A s s e m b l y L a n g u a g e P r o g r a m m i n g

125

languageprogramming.Thesetwo instructions will allow you to changethe stateof a register'sbit in one instruction,without the needfor ANDing or ORing the contentsof the register.bsf and bcf are incredibly useful instructions and will reduce the sizeof your applicationcodeaswell asmake it easierto read. In the previousexperiment,when I discussed how to set andresetthe RPObit of the STATUSregister,Iwas also describinghow the bsf and bcf instructions worked.Here are the bsf and bcf instructions: ,

bsf R€giater, Ail Oporatlo! trovf Regisl€r, nr iorwf 1 << Bit r movlrf Regist€r

rl[cLIrDE

"D15f 584. incn

_coNFIG _FC!{EN_OFF & _IESO_OFF & _BOD_OFF & CPD OlF & _CP_OEF & _!{CLRE_ON & _PWRTE_ON & ICDT_OFF & _IMIOSCIO varLableE CBLOCK 0x20 DLay:2 ENDC t

,

PAGE Mainline

nol) Set

Bit

r For

ICD D€bug

clrf

PORTA

, InitLallze

novlw novwf bef

7 C!|CONo STATus,

i Turn

cllf bcf

ANSEL ^ 0:100 tRIsA ^ 0x00,

bcf bcf

I'RISa ^ 0x00, STATUS, RPo

r/o

Bitss to

off

s) t.} '-{

+r

U

; ).{

m t4

tsd a !

,-t ar.4 t I

r

bcf Reg1ster, Bit oDelelion movf R€gLBter, w andbtf onEl ^ (1 << Bit) movwf Register

qJ ,;-g

Reset

Bil

This descriptionmay be surprising,but this is exactlyhow they work.They do not, asyou might expect,only setor resetthe singleappropriatebit, but they readin the entireregister,modify the appropriate bit, and retum the value to the register.I am pointing this out becausetherewill be caseswhere.if someof a port register'sbits alreadyhavethe desiredvalueand you want to changejust one bit, the bcf andbsf instructionsmay not be the bestinstructionsfor the job.To get aroundthis case,you shouldneverusebsf or bcf in the port registersor other registersthat canbe written both by softwareand hardware. To demonstratethe operationof the bsf andbcf instructions, I modified asmFlashNada.asm by replacing the instructionsthat couldusebsf and bcf with them.It is not a major changeto the application,but it doesshortenit a bit. Like the previousexperiment, asmFlashBit.asm can be run on a PIC16F684in the PICKit 1 starrerkit. title

r \

r

nasmFtashBit

-

Prc15F684

Flashing

rJED"

Thls Program Flashes the PICKit D0 IJED b€tw€en RA{ (Posilive) a'ral RA5 (a€gative) at approxinatseLy 2x pe! secondl vrith o[ly uaing the Bit Set anal Reael InEtructiona Earalware Notes: PIC15E58{ ruDning clock Intselnal Reset is RAll - IJED Poaitive RA5 - LED Negative

at

{ MHz Uaing

the

Int€rnal

Loop: Toggle cllf c1!f Dlaylroolr: rnovlw Eulfff novf antlLw aitdwf

RPo

6d.N

Ccdq)aratorg

Replaces: novf, SIATUS, !t iorlw 1 << 5 rEv$'f, EIAAITS A1L Bils are Digital Replacea: novllr b'001111' rEvwf TIiISA ^ 0x080 Replacea: novf STA1'I St, rt .tld.I!r o:aFF ^ (1 << 5) rlrovrrf SIATUS

t Retsurn Dlay Dlay

+ 1

H€re

1

; Decr€ql€nl t looD

DLay, f sTAqrs, w L << 2 PCI., f,

goto Dlal'Lop nop Addreaa alu€ nop nop bovlrd 1 IJoop aubrf Dlay + 1. f gTATuS, w novf atrdLw L << 2 aaLlwf PCIJ, f goto DlayrJoop nqD Atlflr€aa tlue nqp nqD

t t r t t t

the

nrovlw xorwf

1 << { PORTA,

Z€lo FIag Set? 2 Check Bit Add to the Prograf,r Counter Zero, Lop Alounal Spac€ Cbarlgo in

r z€ro

FIag

tlr€

; Ch€ck for

zero

i

gpace

i

Z€ro

get

Being

t D€clenent

outsiale

Cbanqe Flag

t Toggl.e

RA{

f i

R€Peat

IJIST R=DEC

f'rt

a{l

l , e 3 P I C @I I C I JE x o e n i m e n t s f o r

D0

Inside

ia

Being

Useal

!61'ke Pr€dlko 0{.11.19

Lt6

afte!

for Delay , Itlgh 8 Blts for D€lay r IJow 8 Bile

IJoop

!.1,3

i t t t , i r , i r r ,

off

the Evil

6enius

(D0)

S€t

tn

Experiment 67-Bit 5kip lnstructions

}d 8-!ij

an tsitLe

raamFlaEh

-

PrC15A584

FLashing

rj

LEDiI

llhia Program la the equivalent !o "cFlaah.c" but !,,!itt€n Ln aaE€dibLy lan$rage, laking aalvanlage of AlIr the featureE of PIC UCU aB8dibly langnrage - bit instsrucEion6, bit skiD in8truclions anal dlecredrent anat Ekip inEtructlona.

When you first look throughthe PIC16F684instruction set,you will find executionaddresschangegoto instructionsaswell assubroutinecall instructions.But nowherewill you find conditionalgotos,branches, or other conditionalexecutionaddresschangeinstructions that you traditionallyfind in microprocessorand microcontrollerarchitectures.What the PIC16F684 (and indeedall PIC MCU family microcontrollers)has insteadis the ability to skip the next instructionbased on whetheror not a registerbit is set or reset.The skippedinstructioncouldbe a goto addressor it could be a singleinstructionthat executeswhenthe condition is false(andis not skippedover).\\ese bit skip instructions,althoughbeing somewhatdifficult to understandand applywhenyou are first learningto programthe PIC MCU, are very powerfulinstructions that providean amazingamountof programmingflexibility and single-instruction capabilitiesrarely matched in other processors. And all this canhappenin less than threeinstructions.In this experimentand the next,I will introduceyou to the bit skip instructions and giveyou somepointerson how to implement them in traditionalprogrammingmethodologies. The two-bit skip instructionsare: btfac

btfas

Regial€r,

RegiE!€r,

Blt

Bit

, r r r r r

Skip the 'Bit" if is Reaet skip the "Bil" if S€t (nln)

No:
In asmFlash.asm, I havechangedthe jumps based on addingthe zero flag of the STATUSregisterto "btfss STATUS.Z" instructions.which will executethe next instruction if the zero flag is reset or the one followingit if the zero flag is set.By doing this,I have reducedthe numberof instructionsto changethe execution from sevento two, basedon the zero flag.

Hartbrale Not€a: PIC16E584 running at 4 MHz UEing clock InternaL Reae! ia Uaefl RAll - IJED Positive aA5 - IJED Negative

i.i ;..3

f? the

InternaL

i"r'i

..-.1

1

llyke Preilko 04.11.17 IJIST R=DEC INCIITDE np15f 5811.incn

l:.i; ,t_'

_coNFIq _FCMEN,OFF & _IESO_OEF & _BOD_OFE & _CPD_OFF & _CP_OTF & IICIJRE ON & PWRTE ON & _!iIDIT_OFF & _INTOSCIO

r

f{*

Valia.bleB cBloCK 0x20

!,t J

D]'all:2 ENDC

i

v'. 1,1,,

PAGE ltainline olg

r:*l:l

0

nop

t For

clrf

mRTA

i

irovllr nov$f bsf cL].f bcf

7 cllcoNo STATUS, RPo ANSEL ^ 0x090 TRI61A ^ 0x090,

i Turn

bcf bcf

TRI61A ^ 0x080, STATUS, RPo

I|oop: cllf cllf DLaYIJooP: goto nqp novlw subwf btfss

Dlay Dlay

r r 4 r r 5 r r r

ICD Debug

Inilialize off

I/O

Blt6

to

CdrEraratols

Execute ou! of Bank 1 AIL Bits a!€ Digital BeDlac€s: movLw b'0011L1' rnovwf TRISA ^ 0x080 Retsurn E €culion to Bard! 0

Here aft€! D0 i R€lurn Toggl€ i High 8 Bl.ts for DeLay i I.ow 8 Bitsa fo! Delay

+ 1

$+1

i Th!€e

1-

, D€clement IJoop

Dlay, f STArqS,

i.'a

z

r Skip t Set

c:zcle

if

D€lay the

Zero

InBial€

FIag

S e c t i o nE i g h t P I C @t l C U A s s e m bI y L a n g u a g e P r o g r a . m m i n S

ia

L77

a4

,:? !1 'r='

ril

ir. F.: t1

i,r

golo

ti

Dlaf&oop

al€cf

Dlay + 1,

btfEE

sTATtts, z DLetiloop

goro

"|J

t l

f.€

t'"t

RA{Reaet baf

-l

RMSet: bcf goEo

{u 14

PORTA, 4 RAISets

btfac golo

r t t r r t t t r t t t i t t i t , i , t t

EIse, IJoop llgain ReDlaces: tnovf S!!AT['S, w andllw L << 2 aaLlwf PCI,, f, golo DIayI/ooE, nop nop nqp Decrqlent th€ Higb Blte ltnttl Il EqualB Zelo Replacea: novlw 1 aublrf Dlay + 1. f gTAT{rg, w novf ! << 2 andll1w addlrf rc!, f DIarrIJooD llotso nop nop noD

r loggLe

, RA{ i6

qr,

lb€n

in two instructionslike this: btfsc

PoRTA,

rl

bef

PoRTA,

{

Skip Ove! if, RA{ Reaet Uake RAI i Else, Reset

t

ia

insteadof thesefour: ltrrn

il

On

PORTA, 4 ]Joop PORTA, 4 I,ooI)

(1 == aA{) RA{ = 0t

if

aiA{

, AA{ iE Off,

!

At the end of the application,when I toggleRA4 to turn the LED on or ofl I test its current state.I do so using the btfsc instruction to illustrate that the btfsc and btfssinstructionscanbe usedon any bit in any registerand not just on the statusbits.This ability to testindividualbits allowsyou to implementcodelike this:

Tura

it

Of,f

i Repeat

novf andlLw

PORTA, L << 4

w

btfEs

STAmS,

z

bcf,

PORTA,

4

t Reaal in PORTA t Tesl RA4 to see if il is high or low therr t If zero aet, nel.t akip

which perform the sametask.But the btfscsolutionis obviouslymore efficient(asit is implementedin fewer instructionsand executesfaster)and is much easierto read.

€nfl

"r.N ,-f"{

Experiment 68-tonditional Execution

l*l g 1

r

also be afraid of the amount of work it will take to implement the function. You will likely be surprisedto discoverthat thereis a four-instructiontemplatethat you can use to implement this function for comparing two eight-bitvalues.

,

The four-instruction template that implements the "if Conditionthen Label" decisionstructureare: t"*

}-r

After working through the previous experiment,you may be wonderinghow to implementthe first decision structure that you were ever introduced to-the if statement.If you haveworked throughthe subtraction instructions and the bit skip instructions experiments, then you probablyrealizethey canbe usedtogetherto implementcodethat will jump on condition.Youmay

novf sulrwf btf,B* goto

w Subtsraclor, rd Subtrac!€ntl, STATUS, F].ag Label

where Table 8-2 lists the different valuesfor the optionalSubtractor,Subtractend,#, andFlag.For the less-thanand greater-thancomparisons,the subtraction is arrangedso the expectedlower valueis the subtractend,and if it is lessthan the subtractor,the carry

:& L&.{ 178

l , a 3 P I C @l l C U E x p e ni me n t s f o n t h e E v i I

6enius

Table 8-2 EifferentValuesfor ComparisonTemplate "lf Statement

Subtractor

SubtBEtend

ifA > B then goto Label

# Flag

s

It

C

ifA >: B then goto Label

c

ifA < B then goto Label

s

C

ifA <: B then goto Label

c

C

C

r4

!&'ke Pledlko 04.O9.2L

, ,

tq h?$

IJIST R=DEC INCIjTDE,tp16f 684. inc.

I lt

CBIJOCK 0x20 D€claration

VariabLe

,

*d

l".

ENI'C PAEE

ifA == B then goto Label ifA !: B then goto Label

s

1g i,{

Z r R€quireil

flag is reset(zero).Thiscodetemplatemay seemlike an advancedusageof the carryflag,but you shouldbe able to figure out operationslike this by reading throughthe PIC16F684datasheetand experimenting with the subx{ instruction.Do your experimenting with differentvaluespreviouslyloadedinto WREG and check the results (both the numeric result of the subtraction operation aswell ashow the STATUS bits are set). When using this template,remember that the WREG's contentsaswell asthe stateof the C. Z. and DC STATUSflagshavebeenchanged. The asmCondition.asm programdemonstrates how thesefour statementsare usedto implementdifferent decisionstructuresusingthe informationin Table8-2 (and embeddedin the sourcecode):

novhr novwf novlw movwf

L2 i 34 j

,

novf subwf btfs6 goto

i, n j, w sTATus, c ErlorlJoop

;

movf subwf btfsc golo

j, w i, !t STATUS, C Errorl,oop

,

if

novf, aubnf blfac

i, w j, w STATttg,

,

Lf

DemonEtrate

rif,

Initialize

MPLAB ICD2

Teats Variable8

if

> j

i

f)0

tshenErrorlooD

I

t i

>= j

!he!

Efror].oop

i

== j

lhea

ElroltooD

Z

H, goto

r Finish€il,

$

Evertrthing

r ComDare Operation i wolk correctly

Okay ilidn'l

rlovf, subwf btfB* gotso

iDstluctsion6

a!e:

Subtractor, w SubElactendl. w sTATus, FLag Labe1

i Ithere the nsublraclortr, andl nFlagn ale DefLneA as:

nsublractenAn,

i r

lleldlware !ilote6: PIC15F584 running

at

4 UEz

Looking at the four-instruction template and the code for this experiment,you can probably understand how to apply the four instructions,but, you may be unsure how to apply it when one of the condition parametersis a constant.In thesecases, the literal instructions movlw and sublw replace movf and subv{, respectively.For example,to implement the highlevel if statement:

in

CI ni H

EI X {D i J

r*tr if

r "if Statdlant" lsulrtractor lS\rbtractenal t --- ---- --- ----- --+-- --- --- --+---rif l|>B then !ab€1 B A rif JD=B rif A
l.J.

s

ElrorlrooD

eaal

The fou!

r-{

,*

goEo

:ghls exD€rim€nt il€tnonEtrates a silE)Le se! of four iastructions that simulates tbe oDeration (conititioD) goEo IJab€Ln high 1evel of a .if langnrage slat€ments.

rf

s'\

Errorloop: "aamconaition litle OgeraEioDs ia Assenbler"

f,or

l * lELas lsl lcl lsl lcl lcl lBl

Sfumrlator

c c c c z z

(1

> 47)

th€n

goto

Lab€l

hr.

o

you would usethe code: llovf Bublw btf6s goto

i, w 47 STA!!US, C label

,

if

i

> 47 thea

Label

Using the four-instruction template for the "if Condition then goto Label" decisionstructure,I suggest

S e c t i o nE i g h t P I C @1 1 C l JA s s e m b t y L a n g u a g e P n o g n a m m i n g

L7g

that you try to come up with ways of implementing highlevel statementssuchas: ((A

if

< B)

&& (A > C))

then

Ranse].ab€I

soto

or:

in PIC MCU assemblylanguage.It is actuallyeasier than you might imagine,althoughbeforeyou start looking at differentprogrammingstructures,you shouldassumethey canall be implementedusingthe if statement(presentedin this experiment)alongwith the goto instruction.

(A < 4?)

wbile

ExFeriment69-decfsz Looplng )

//

lthil.e

.r{

ta t llt

sl/

I I

!. z-i

{T

After the previous experimentsshowing how conditional execution and decision structuresare implemented in the PIC MCU, the simple if, while, and for statementsof C probablysoundgood.Although these statementsare not built into the PIC MCU assembly language, thereis one instructionthat makesrepeated loopingquite a bit easier.Itis the basisofjust about everyPIC MCU assemblylanguageprogramever written. The decfsz(or decrementfile register and skip on zero result)canbe usedto executea loop a setnumber of timesasdemonstratedin this experiment'sprogram. This instruction decrementsa file in a similar manner to the decfinstruction,which decrementsthe contents of the registerby one and storesthe resulteitherback into the file registeror the WREG. But the decfszdoes not changeany of the STATUS register bits. Instead if the resultof the decrementis zero,then the program counteris incrementedbeforethe next instructionis fetched.When this instructionis usedin a loop,it will count down and causeexecutionto fall out of the looo after a setnumberof iterations.

ci3

rraamDecfaz -

litle

,;-j { . F-i

//

at

Finishett,

4 MHz in

Loop

Forev€r

Simulator

Ityke Pr€tlko 04.04.14

iJ.i

b{

(1 == 1),

Hartlware NotseE: PIC15F684 ru ring

u|l

U

elihw

Domonatrate Lnstruction

lhe for

,,Cn Equlvalent

rohile

(i

180

Operation r,ooDing.

of

LooD',

ualecfsz"

the

Coale 3 //

LooD Arountt

// //

Do nothing Declenenl

7x

!= 0)

t = i - 1t

i v t

alecfEz

in the Loop loo9 Counler

LISI R=DEC rNcr,uDE "p15f 684. inc" t

varLablea CBLOCK 0x20

j'

ENDC PAGE olg nop movLw nowrf

0

7 i i loop h€re t Do nothing

nop alecf,az goto goco

i,

f,

7x in

LooD

; i = i - 1 , i f r € s u l t = = 0 , i akip

IJooP

r Finiaheal,

just

loop arounal

enal

Along with the "decfsz"inshuction there is the "incfsz" (incrementfile registerand skip on zero result),but this instructiondoesnot have a "standard" uselike decfsz.As I familiarizeyou with how the PIC MCU works and how you can optimizeyour applicationsin very surprisingways,you will find that both the decfszand incfszinstructionscan be usedto make your applicationsvery efficient.Until then, as you first start working with the PIC MCU and write your first applications,I recommendthat you remember to usedecfszasjust a way to executea loop reDeatedlv

l , e 3 P I C o l ' l C UE x o e n i m e n t s f o r

the Evil

Genius

(-J \.

Experiment 70-5ubroutines

/t\

9ub1: cal.L

Sub2

sub2: call

Sub3

caLt

When you are leamingto programthe PIC MCU in assembler, it may seemlike everyinstructionhassome speciallittle trick to be awareof Fortunately,this is really not the casefor addingsubroutinesto your program.They canbe addedquite easily,and the issues that you haveto be awareof are quite standardfor smallprocessors. The operationand differentaspects of subroutinesare demonstratedin the asmSubr.asm program,which canbe simulatedin MPLAB IDE. 'raar6ubr tltsL€ ODeration,l

-

subroutsine

This program Ehows holr Subloutsines th€ PIC UCU. llaldkoaie Notes: PIC16F68{ rultding

al

{ t{Uz in

work

SimulaEor

PAGE 0 for

MPIAB ICD2 "rer1w"

nlovlw caU

0x55 SubRetLw

t Ca1l

lrcvlw caLl

0x7B StlReturn

i Trt agai4 with i With',raturn"

calL

Subl

r see if you can trest ; Subroutiaea

golo

$

; When &aecutiqr i Loop Eorever

Returzrs

r subloutines Subnetlw: lellw 0nAA

i Retuh

in

SubR€tun:

t Stanalaltl

Subroutine

a value

i DeDlh

Check,

Ca11 Next

F,

Next

L-t

&

r{ D€I)th

Check,

Ca1l

Next

r*"

sub5

t Depth

Check,

Call

N$
*"1

Subs: call

s\rb5

t D€pth

Check,

CaII

Ner€

sub6: call

subT

i D€Irth

Clr€ck,

caU

Ner(!

SubT: cal.L

SubB

i DeDth

Clteck,

CaIl

N€xts

SuIt8: ceLl

Subg

t D€pth

Check,

Ca11 Next

, FiniBhed,

!!

tr?} Fq

IieEurn...

**

eaal

LIST R=DEC INCT,IIDE trDl5f 68{. inc"

t R€qui!6al

Call

in

!lyk6 Pr€atko 0{.11.20

olg aoD

Check,

Sub{

sub{! call

subg:

i Ir€Dth

with

a Subloutsine

Subloutirre

10

Uere,

$REG

ttetuh

Data is t'?ically passedto the subroutineeither by usingglobalvariablesor loadingWREG (and,optionally,FSR) with the input data.Returningdata canbe passedusingeither one of thesetwo methods,by setting STATUSflag (carry,digit carry,or zero)values,or by returninga constantin WREG. The first subroutine in asmSubr.asm returnsdatausingthe retlw,which loadsWREG with a constantvaluebeforeretuming. This methodprobablyseemssomewhatredundantand evenuselesEbut it is criticalto implementingread-only arraysin the PIC MCU. It is alsothe methodusedto return from a subroutinein the low-ransePIC MCUs. so it doesn'thurt to be awareof it. The programcounterstackin the PIC MCU is only eight-valuesdeep.Callingrnorethan eight nestedsubroutines(asI do in this experiment)will resultin the codebecominglost in the subroutinesand continually runningthJougheachof them.You may havediscoveredthis when you simulatedasmsubr.asm, but you will neverapproachthis limit in normal programming.The only time I would expectyou to havesome problemswith losingexecutionreturn for a subroutine is when implementinga recursivesubroutine(or a subroutine that callsitself).

S e c t i o nE i g h t P I C @t l C l JA s s e m b l y L a n g u a g e P n o g r a m m i n g

181

F.

ry in

ExF er im ent 7l- Def i n i n g a n d l mp l e m e n ti n gR rra g s cbLock Array:

0x20

6

enalc

The lastoperationthat you shouldbe awareof is that of initializingarrayelements.Thesimplestway of accomplishing this is to write directly to eachaddress of the variable.For example,if Array wasto havethe first six prime numberqit could be initializedas: The lastmajor assemblylanguageprogrammingconceptto learn is declaringand accessing the datawithin arrays.Like other smallprocessors, the PIC16F684 microcontrollerprocessorprovidesa singleirulexregister (calledFSR in the PIC MCU). which can accessall the registers,both variablememoryand the special functionregisters.The conceptof indexedaddressingis simplyusingan indexregisterto accessarrayelements. The PIC MCU implementsindexedaddressinga bit differentlyfrom other chips,asthe registerspointedto by the indexregisterare accessed via the useof a shadowregistercalledINDF. In practicalterms, indexedaddressingis not any more difficult to implement in the PIC MCU than in other processors:The only issueis rememberingto specifyINDF whenreading from or writing to the registerpointed to by FSR. Therefore,to read a byte from an arrayat position n, you would usethe code: firovf aaLllw

n, w tlfiay

rnovwf tnovf

FSR INDF,

t r i r w r

Get offset of A.fiay Ele!$ent Adal stalling atLlless of the Arlay Stole in FSR (Inalex Regdster) n}.rraylnl n TJoaal WREG with

Similarly, to wdte the contents of WREG into an arrav element n. vou would use the code: movwf

Tenrp

adau.\r

Array

novwf novf, movwf

!'SR Tenp, IIIDF

rd

t r r ; r i t r

Tefiporarily atore the value G€t Of,f€et of, the Al.ray EL€ments Afltl starting address of, the Brray Store A.rlay ELenent Addless Retrieve saveil vaLue Save value.

Declaringarrayvariablesis very easyto do with the CBLOCK directive,asis the ability to specifythe differenceto the next label.For example,for the previous readingand writing examplecode,if the Array variable wassix bytesin sizeand you wantedto make surethe next variabledid not occupythe samespace,you would Dutin the followins statement:

t82

mowlw novwf novlw novwf itrov1w monnf movlw nowrf movlsr rnovwf novl\d novwf

L Array 2 Affay 3 array 5 array 7 array 11 Array

First

i

Element

i

Seconal Ef,ement

i

lhird

El€n€nt

i

Forth

El€ment

i

Fifth

ELem€nt

t

Sixth

E1ement

+ 1 + 2 + 3 + 4 + 5

When doingthis type of initialization(or even alray elements),rememberthat the directlyaccessing first elementhasan offset(and index) of zero,and eachelementhasan inderoffset that is one lessthan the elementnumber. This is really all thereis to working with indexed for byte arrays. addressing asmPCKLED3.asmis a demonstrationapplication in which rhe LEDs on the PICKit 1 starterkit flash from D0 to D7, andit waswdtten usingarraysfor the PORIA andTRISA values. title

"asnPKI.ED

3 -

PIcKit

Running

LED"

This program copi€s th€ op€ration of CPKLED.e and Flashes the 8 LEDg on the PICKit J. PCB in the vaLues fo! the IJEDa Sequence by Storing in Arlays anal lhe TRIS registers Haralware Notes: PIC15F68{ running at 4 MHz Using InternaL cLock circuit Run6 on PrcKit 1 PcB Orisinal

code:

int i, j, k, cha! r,Efrya1uel6]

char

the

TRrsvalue

= (0b010000, 0b100000.

[8]

0b010000, 0b000100, obL00000. 0b000100. 0b000100. 0b000010 )t = t0b001111. 0b001111, 0b101011, 0 b 1 0 1 0 1 1 , 0b011011, 0b011011, o b x 1 1 0 0 t , 0 b 1 1 1 0 0 1 t)

l , e 3 P I C @l ' l C UE x o e r i m e n t s f o n t h e E v i I

6enius

r main( ) i { , , ,

PORTA = 0t CMCONo - 7t ANSEL = 0t

;

whil.e(1

,

{

== 1)

// //

T1u,tii off Cdq)arators Turn off, ADc

//

Start

//

loop

(i = 0r i < 255i i++) // for tor (j = o, j < 729t i++li

r r

at

I,ED 0

Forever Snqple

Delay

toop

PORTA = TJED\ral.u€ [k] r i // slecify LED Outpur TRISA = TRISvalue [k] r r i k = (k + a) ea A, i // Increnenr k within range of 0-7 i , j i // eTi}lw , } // E!r'I CPKLED t t i lil]ke Predko r 04.11.07 ; t I,rST R=DEC INCLUDE "p15f684, inc" FCIIEN-OEI' & -IESO OFF & _BOD_OFF & -CONFTG _CPD OFF & _CP_OFF & I4CLRE ON & _PWRTE ON & _WDT OFF & _INTOSCIO variables cBr,ocK 0x20 LEDvalu€:8. TRISValue:8 Dlay k ENDC r

PAGE Dlaj.nline r olg

of

movh, E*plicitly nrovwf novwf Inovlltr' novwf novr,rf novlvr rnovwf movwf movlw movwf novwf

b,001111,

i lJoaal TRISvatue

TRISVaLue TRISValue b'101011, rRlsvalu€ Tlllgvalue b,011011, TRISVaIUe TRISVaLue b,11X001, rRrsvalue TRISValue

+ 1 ; NO[E:

DLay

btf,ss soto ilecf,€z goto

SAATUS, z S-4 D1ay, f S - 5

+ G + 7 after ' Return r RBO Toggle r Eigh I Bits

r D€crenrent , WREG ? 256;{ t Repeat

i PoRTA = LEDValue lkl novf k, rnr IJEDvalue

novt^'f

FSR

novf mowrf

INDE, w poRTA

r TRISA = TRrsvalue rnovf k, w

nop

r For

ICD Detrug

cllf

PoRTA

novLw Inovwf bsf clrf bcf

7 OTCONo STATUS, RPo ANSEIJ ^ 0x80 STATUS, RFo

clrf

k

, Start

novl.\r novwf novLw novwf novl.\r no\rwf novln novwf movlxr movwf nrovlw nolr!!-f novlw nol'$rf novl$ rno\rwf

b,010000, IiEDValue b'100000, LEf,ivalue b'010000, IJEf,iVaIu€ b'000100, LEDValue b,100000, LEDVal.ue b,000100, IJEDValue b,000100, IiEDVal.ue b,000010, lEDVaIue

r Load I,EDvalue

i Initialize i to Off off i turn

r/o

Cdpar.ators

r A11 Bits

are

Bits

aaldtut rnovnf

T&ISValu€ FSR

rnovf O"t irovwf bcf

INDE, w STAIUS, RPo TRISA ^ 0x80 STATUS, RpO

incf anallw novwf

k. 7 k

goto

Loop

w

Delay for

the

arlal

Delay

conlents

of

255x

r ; r r r r r ,

lJoad the Offset for IJEDvalue AtLl to Start of I;EDvalue Array Store AaiitresB in hdlex Register cet rJllDvalue [k] save in poRTA Register

r ; r r r r r

c€t lhe Offset for Trrsvalue AtLt to the Start of Array Slore Adalress in Index Register Get TRrSValue [k] Save in TRIS:A Register

[k]

asrnPKJ,ED

O

Pairs

+ 4 + 5

$ + 1 s+1 -1

addl"w

in

+ 2 + 3

r6op: cltf clrw goto gloto aattlLw

LEDS are

the Active , rncrefi€nt lange of i Keep Withia

,

LED O-7

Repeat

Digital end

+ 1 + 2 + 3 + 4 + 5 + 6 + 7

with

D0 E>E,l.icitly

For ConEideration In this chapter,I havereviewedthe basicassemblylanguageinstructionsand givenyou a basicprogramming templateto work from.Along with this,you haveexperiencewith the MPLAB IDE and with programming in C.You shouldbe readyto start programminga PIC MCU in assembler, only you may not feel that confident in your abilitiesto do so from scratch.Chances are if you havea programmingassignment, you will be

S e c t i o nE i g h t P f C @i l C U A s s e m b l y L a n g u a g e P r o g r a m m i n g

L83

able to copy asmTemplate.asm into a specific subdirectory for your application,renameit to the application name,loadit into MPLAB IDE, and then just stareat it becauseyou don't know whereto begin.Before going on to more complex programming assignments,I would like to giveyou someguidancein structuring andwdting PIC MCU assemblylanguageprograms. The basicpartsand sequenceof the assembly languageprogramare asfollows: 1.

2.

fr "r"{

s

t{

rU .F{

u) .'\

Use nop as the first instructionso an MPLAB IDE incircuit debugger(MPLAB ICD) module can be usedto help you debugyour application in circuit.Although you may not havean ICD (or ICD 2) that you can usefor debugging,it's a good idea to alwaysput this instructionin so you are in the habit of being ready to debug your codewith the ICD.

Perform the necessarybank 0 initializations.I like to put in the variableinitializationsfirst, followed by the hardwareinitializations. Rememberthat variablesshouldalwaysbe initialized(evento zero) usinga clrf instruction. 3. Perform the necessarybank 1 initializations. Theseshouldjust be hardwareinitializations; you shouldnot put any variablesin bank 1 until you are very familiar with PIC MCU assembly languageprogramming.Rememberto XOR the registeraddresses with 0x080to ensureyou do not get a messageindicatingthat you are accessing a registerin the wrong bank.When you work with other PIC MCUs that have hardware(and variable)registersin banks2 and 3, you will haveto repeatthis stepfor each one of the registers. 4. Virtually all microcontrollerapplicationswill executeforever,taking in input, processingit, and then passingit back out.After the initializations,the codeshouldstart executingthe loop code. 5. Next, read your inputs.This can be simply polling the I/O pins or readinghardwareregister values. 6. The inputs are then processed. This processing can includecomparisonsto expectedvaluesor arithmeticcomputations. 7. Onceyou haveprocessedthe inputs and understandwhat shouldcome out of the application, you can output them.Just aswhen you read your inputs,outputting could consistof writing directly to I/O pins or to hardwareregisters.

If somedelayis requiredin the prograrn,it shouldbe done here.Creatingdelayswill be explainedin the next section. 9. The loop codeis complete.Jump to the start of the loop and begin again. 10. Define the variablesto be usedin the program. I like to definethem last becausechancesare I addedone or two when I createdmy program, and this way I can go back and make sure everythingis definedusingMPASM assembler (when the programassemblescleanly,then all the variablesare defined). 8.

To illustrate how a program is created using this methodology,I createdasmButton.asm. In this program,I haveput in commentlinesthat startwith #### to indicatewhich of the 10 stepsis beingimplemented in that and the followinglinesof code. "asnButton

!181€ IJED

- prc15r58{/prcKit

Butstotr

ONN

i t

Thia lrheu

Program luras the Button at

i t t t t t t

Haralwale Notea I PIC16F58{ run'riag a! { MHz UaiDg Internal Clock External Rea€l ia U6etl RA3 - PICKit Button RA4 - LED Poailive RA5 - IJED N6ga!iv6

i r ,

Uyk€ P!€tlko 04.LL.O7 IJIST R=DEC I!|CLUDE "p16f68{.

ou tlr€ RA3 is

PrcKit,s Dreaseal.

the

inc.

& _rEso_oFF & _BoD_oFF & _coNrrc _EcltEN_oFF _CPD_OFF & _CP_OEF & _IICIJRE_OFE & _PWRTE_O!{ & _IIIDIT_OFF & _INTOSCIO valiablea CBIOCK 0x20 - 10. *lt** r Tetlp ENDC t

t

PAGE l,lainliae or9

of

Put

in

(if

Ehe valiab16a

0

r #### - 1.

Put

ia

nq9

nnoD" inatructsion r ror

r **#* - 2. Prrt ia trbvltr oriFF novwf PORTA

r€quir€al

"Bsnlr 0 rnitializalions" ; !'lake AU PORTA Bits

the EviI

for

ICD Detnrg

k{ l , e l P I C @l l C U E x p e ri m e n ts f o r

requir€tl)

cButton

l"l

184

D0 rrED

6enius

High

rcvhr 7 i Iovwf CIICINO .BaDk 3. Pul iu r #**# bsf ATAttlS, RPo clrf .NISEI. ^ 0xg0 , novlw orroFF ^ ((1 << t rcvwf IRISA ^ 0x80 bcf sTAnts, Rpo , **** IJoolr I t ##** rcvf,

- {.

LoD

Ertry

- 5. R€ad ln PORIA, w

Tuln t

off

Cclq)arators

InLtializalionsn

A11 Bits ar€ Digltal 4) | (1 << 5)) RA{/RAs a!€ Digita]' OutDuta

bovwf , #*** e'vbr btf,sc novlw t **** rdvtrf r **#* r lt#lt* golo

TdE) for , Store 5. Proc€ss rqrutss 8,011111' r DO G? Tetqr. 3 t If, RA3 ls 8,111111' t No, Off 7. Outpur proc6s6edl rDput PORTA (tf Required) 8. D6tay 9, Relu!'r to the start of IJooD , Rerr€ats

qt

RA3 Check

g6t

tb3n

th€

L.oolr

trYesi

o p

end chech

rt

o

Poiat

Intrirls t Want to

o

0t

R.tr3

f",

g

o

Fl

t,

ct h..

o 5

S e c t i o nE i g h t P I C @f l C l J A s s e m b l y L a n g u a g e P n o g r a m m i n g

185

Nine

Section

PIE@ Microcontroller HEsemblg LanguageFleEource Floutines

1 Prc16F684 Red LEDS 1 Yellow

LED

1 0.01 /rF capacitor tYpe)

(any

100O resistors 1 I

Breadboard

1 3-cel1 DMM

AAA battery

pack

AA batteries

Needle-nose pl iers Wiring

kit

If you wereto askme whetherusingC or assembler languageis the most efficientmethodof creatingcomplex PIC MCU applications, I would answerthat the bestapplicationsare written usingbotlzprogramming languages. C is excellentfor high-levelprogramflow wherecomplexconditionaland adthmeticstatements are normallyused.Assemblylanguage programming is necessary whenyou havea preciselytimed interface requirementor logic/arithmeticoperationsthat must be very efficientlyimplemented.Although in the rest of the book, I concentrateon assemblylanguageprogramming,I want to point out that you havethe opportunityto add assemblylanguagecodeto your PICC LiterMcompilerapplications. Thereare a number of thingsyou will haveto be awareof beforeyou stafi addingassemblylanguagecodeto your PICC Lite compilerapplication. The first issueto be addressedis whetheror not your applicationcodewill consistof a mix of C statementsand assemblylanguageinstructionsor if the applicationcodewill haveonly one of the two programminglanguages. Even without looking at how the PICC Lite compiler'sbuilt-in assemblerworks (which is requiredfor an applicationthat hasboth C state-

mentsand assemblylanguageinstructions),I would tend to go towardshavingseparatefiles for assembly languageand C sourcefiles.The two codesources would be individuallycompiledinto .obj files (often calledobjectfiles),which would then be linked together.MPLAB@IDE handlesthe compiling,linking,and source-codeJevel debuggingchoresvery efficiently,with eachsourcecodefile displayable. An importantadvantageof usingmultiple sourcecode files is that subroutinefiles canbe sharedvery easily, especiallyassourcecode,which would eliminatethe possibilityof a developerchangingcodethat is already runmng. The problemwith linking multiple files into an applicationis the additionallearningand work that is required.For the applicationsin this book, I don't feel that it is appropriateto attemptlinking multiple files together.Instead,the examplesof mixed codesources will primarily usePICC Lite compilerC sourcecode with inline assemblerstatements.The assemblylanguageinstructionscanbe addedindividuallyusingthe directive: asm(,'PIC UCU Instruction"

't87

)t

..::: " r1i : l .i{

:*-'i 11 .!.i

r,{a a'i '.-'j

i"r;; a'\ l-:i t::ii

i 1'r

i.t') f',,,.,

..-t

or they canbe addedasa predefinedfunctionstatement.Earlier in the book, I usedthe NOPQ;builfin function in a number of applications.This function insertsa singlenop insffuctionin the codeand allows me to set simulatorbreakpointsin the application wherethe statementsor operationseitherdo not seem to skip randomlyto other instructionsor to setbreakpointsresultsin an MPLAB IDE simulatormessage. Along with the nop instruction,the cleartheWatchdog Trmer(clrwdt) instructioncan alsobe addedto a PICC Lite compilerapplicationin this manner. If you havea nurnberof assemblylanguageinstructions,you shouldindicateto the compilerthat assembly languageinstructionswill follow by usingthe #asm directive, and that you are finished by using the #endasmdirective.These directivesand instructions are bestplacedin uniquesubroutineslike the followrng one: int Aaaenibl:rDomo ( Lnt SqvaLue) ( lhe Squale of // Calculate

nvaluen

= SqVaIue, to Squar€ in Mesrory lJocation // save value caa access uniquely // aaa€lible! *aam movf w // Get uulliDlicand _al, clrf _gquale + 1 clrf _gquare ASt ooD: Loop Back to Iler€ until ai

atLkcf blfac incf alecfaz

t'i

gquale, Etatus, _gquare f _ai,

f

i 0 i + 1, i

Afldl Value to sguale ou€rflow? f Decrement Rep€atedl Aalalit'ion Counter

golo *entlaBm !€turn //

,

ASIrooP

t Retura

lo

Trl.

agaitr

Squalei wrd

AaaeniblyD€mo

Thereare five thingsyou shouldnote about the codein this function: . .

The addition of the leadingunderscoreto variable namesin the in-line assemblercode. The needto declaremost variablesas"char unsigned"variables.This isn't readily apparent in the code,but eachbyte variableshouldbe declaredas"char unsigned"to avoid negation issueswhen executioncrossesbetweenC and assembler.

.

The lack ofbit labelsfor statusor any other registers.

. .

Declaredregistersare all lowercase. You do not havethe $ operator to help you avoid comingup with your own labels.You will haveto put in labelsfor every for loop.

For the mostpart,thesedifferencesdo not make writing inJine assemblermore difficult,just different. This is why I recommendthat you add inline assembler instructionsonly whenyou haveto.The PICC Lite compiJer is a remarkably efficientcompiler.andthere will be only limited situationswhereit is bestto combine C statementsand assemblylanguageinstructions together.

i--: f -l .

Experiment72-LoSic 5imulationUsing the PlEl6F6Btl a:\! |*

1 P rcr.6F58 4 Red LEDS

+]

I

i']

YelIow

LED

Ji1

1 0. 01 pF capacito! tYPe)

,*

2 100O !esistors

(any

1

,,,{ ! t

DMM NeedIe-nose pliers ttiring

ir**

I

Breadboard

I

3-ce11

AAA battery

AAA batteries

kit

il:*a ri,l

i.1

188

l , e 3 P I C @l " l C l E J xperiments for

the Evil

6enius

pack

I hope that I haveimpressedyou with the power and capabilitiesof the PIC MCU. Now I'm goingto try to you andshowyou the minimumthatthey underwhelm canbe programmedto do.Thisis a good time to go back and showyou how truly good the PICC Lite con.rpileris and showyou a little trick tbr creatingyour own PIC MCU applications. In thisapplication,Iam goingwe will createa two-inputAND gatefrom a PIC16F684. The circuit that I havecomeup wlth is very simple(seeFigure9-1)andcanbe wiredon a breadboald(seeFigure9-2)in iust a coupleof minutes.I wantedthe LEDSto be lit when the input wasa 1 andoff whenan inputis 0.Todo this,I takeadvantageof the halfVdd voltagethresholdon the PIC MCU pins.Red LEDs havea voltagedrop of 2.0volts, whichis greatcrthanthe 1.5-volt thresholdof thc PIC MCU input pins whenthe PIC MCU is poweredby 3 v o l t sW . i l h a I { l { l Qc u r r e n t - l i m i l i rnegs i s t oi rn s e r i e s . the LED can eitherbe shortedto ground(and turned ofl) for a 0 or left on in circuit to passa 2.O-voltinput to the PIC MCtl. I\n pointingthis out becausethis circuit will /rol work with a 5-volt power supply.

Here is the first experimentlor you to try out. Find the voltagelevel at which the PIC devicetransitions from a 0 to a 1,and whenthe red LEDs are wired asin this circuit.As part of this exercise,make a guessat what thrstranslationvoltagewrllbe beforeyou add the variablevoltagesupply. The assemblylanguagecodefor the application, asmlogiccate.asm,is very simpleasyou would expect.It makesall the input pins digital I/O and then polls the two input pins (RC3 and RC4).Thenwhen the inputsare both high,the output of RC2 is driven high,and the LED connectedto it is lit. rrasnlogiccate titsle sinulationrt r This r like

program a Eingle

-

Losic

causea lhe Prc15F684 2 hput a.ND Gate.

i garalxrare Noles: PIC16F584 rurlniflg , Clock

at

4 !I$z Uairg

to

behave

the

hEernal

Eardlware Notes RCA:RC3 - hpul - Output RC2 llyke Predko 04.11. 19

PIC16F6B4

LIST R=DEC INCLUDE'rp16f684.incrl -CONFIG -FCI,IEN-OFF & _rEso_oFF & _BoD_oFr CPD OFF & CP OFF & I]IICLRE ON & .PWRTE_ON & WDT OFF & Ir\ITOSCIO t

variables CBLOCK 0x20 ENDC

PAGE t Mainline

Fisure9-l

PIC microcontrollarAND gute

org nop

r For

clrf

Initial.ize to Off Turn off

nov$rf bsf clrf nov1n

CMCONo STATUS. RPo AlilSEL ^ 0*80 b'111011'

rnonr,rf bcf

TRISC ^ 0x80 STATUS, RPo

IJoop: btf,ss goto btfss goto noP bsf goto

Fiqure9-a Breodboard AN D gate circuit

ICD Debug

PORTC. { NoMatch{ PORTC. 3 NoMatch3 PORTC, 2 ],oop

I/o

Bits

comparators

Al.L Bits are Digilal RC4:RC3 hputs, RC2 Output

Relurn llere af€er Delay 'f€st Input Bits

Match cycles Both are set

S e c t i o nN i n e A s s e m b l y L a n g u a g e Re s o u r c e R o u t i n e s

to

se!

r.89

Nouatch4

!

goto NoMatch3: bcf goto

t 1\ro Cycles Noltatch3

Past

t ReEeE the

OttDuts

PORTC, 2 Loop

end

To comparethe operationof my assemblylanguage codeto what the PICC Lite compilerproduceqI created a similarapplication,clogiccate.c.This program polls RC3 and RC4 and outputsa 1 on RC2 whenboth inputsare 1,just like in asrnlogicGate.asm. Sincluile clogiccate.c /* Prc15F5g4

J|3 t !

Plogram

outputg

Sinulate

a "f

an AND cate

if

Two Inputs

on a

ar€

u

,

& ICDTDIS & PWRTEN & !4CLRDIS & -CONFIG(INTIO UNPROEECT \ & I'ITPROTrECT& BORDIS & IESODIS & FCMDIS ) ,

nain( )

t PORTC = 0, CMCOIiIo = 7t ANSEIJ = 0, TRISC2 = 0i

(

== 1)

// // //

Turn off CdnDarators Turn off aDC Make RC2 Output

//

Loop

Forever

( (1 == Rc4 ) && (1 == Rc3)) Rc2 = 1, OutDut Eigh // Both High, else RC2 = 0, // E1s€, Low output if

| ,

;'d

ll

/ / er|tu" Endl closiccate

As a follow-upto the introductionof this chapter,I want to showyou the efficiencyof the assembler instructionsgeneratedby the compiler.After I tested the operationof both applications,Itook a look at the codegeneratedby the PICC Lite compilerby clicking on "View" and then on "DisassemblyListing."The followingcodewasdisplayedin a new window on the MPLAB IDE desktoo:

lJ"6 --C:\wriling\Prc Geniua\Cotle\cT,ogiccate 1r *inclual€

190

Program

outputs

a "1"

if

rlro

In!,uta

a?e

1 0 : myke pretlko 11: 04.11.19 L2. 13: L4l CONFTG(TNTIO & W!||IDIS & PYIRTEN & IICIJRDIS UNPROTE & TTNPROTECT & BORDIS & IESODIS & ECMDIS) t

(

231 24: PORTC = 0t 0003F3 1283 BCE 0x3, 0x5 00038{ 187 CLRF 0x7 25: CllCONo = 7r // 000315 3007 !4OvLw 0x7 0003F5 099 uovuF 0x19 26: iNSEL = 0r // 000387 1683 BsE 0*3, 0'r5 0003F8 191 CLRF 0x11 = Oi 27t a&lsc2 // 0003F9 L10? BCF 0x7, 0x2

29: 30:

w h i L e ( 1 -= 1) (

//

rurn

off

coltll)ara

Ilurn

of,f

,rDC

Make RC2 Oulput

Loop

Forever

== Rc{ ) e& (1 == Rc3)) BCF 0x3, 0x5 BrFSC 0x7, 0r.4 BrFSS 0x7, 0x3 GOTO 0x3f9 ll Both Hlgh, BSF 0x7, 0x2

j;

while(l

8:

RCA - Iq)ut RC3 - Iry)ut RC2 - o|rtput

a

!,-!l

i,

This

1 9 : ints i, j, 20l 2 L l rnain ( )

RC{ - Input RC3 - rnput RC2 - Output

int

{:

L7z -

ml'k€ grealko 04,11.19

L t_:

an AllD Ciate on

Simulate

Nolrlatch3

tti

Thia

c -

2, /+ cLogj.ac ale. PIC15F6

Evil \cIJogiccate.

c

0003FA 1283 0003F8 1A07 0003Fc 1D87 OOO3FD 2BF9 32t RC2 = a, 0003F8 1507

OutsDut

You can make a couple of conclusionsfrom the resultingassemblylanguagecode.Thefirst being,the disassemblylbting is not complete.The closingbrace for the "while(1 - - 1)" statementand a"goto 0x3fa" instruction.which returnsexecutionto the start of the comparison,are both missing.Tosimulatethis applica"pin stimulus"featureof tion, I usedthe asynchronous the debuggerto changethe statesof the input pins. The secondconclusionyou canmake is that the PICC Lite compilerisn't stupid.It wasableto convert the two-termif statementinto just three assemblylanguageinstructions. And at the sametime,it wasableto note that resettingthe TRIS bit RC2 in bank 1 is the sameasresettingpin RCZ in bank 0. Later in this section, I will provideyou with a set of macrosthat will allow you to virtually write your own highJevelcode in PIC MCU assemblylanguagewithout havingto understandhow the differentinstructionsoperate.But the codeproducedby thesemacroswill in no way be asefficientasthe previoussnippetof code.

l , a 3 P I C @l ' l C UE x o e r i m e n t s f o r

the Evil

Genius

how The three-instructioncodedemonstrates in the PIC operationscan be created sophisticated just MCU using a few instructions. Two-bitinput AND statementsand OR statementscanbe producedusing the following templates: i

AND Code 3 Instruclion btfsc Regislerl, bitl

btf,ss goto

Register2,

biL2

SlitDNotTrue

r Coale E:.ecutedl Both Bits are

ANDTrue:

;

3 Instruction OR Coale btfss Registerl, bitl btfsc goto

oRNot True:

Bit Input r If First is 0, Jump to not True lnput i rf Seconil Bit iB 1, .runp to True r One or Both Bit hpurs is 0, nnotn

Register2. oRTrue:

bil2

if 1

Bit ia 1, r If First iIump to "True" r If seconal Bit is 0, Jrrnp to "Fafse" are t one or Bolh Bits

I r coale Execut€al if Both Bits are 0

Thesetwo snippetsassumethat Tiue is high.They canbe easilymodifiedifTiue is low for one or both bits;simplychangethe btfssto btlic, and visaversa.

If you are a student,I shouldremind you that it is not a good ideato w te your applicationin C and then usethe PICC Lite compilerto generateassemblylanguagecodefor your applicationfor a numberof reasons.First,the displaydoesnot labelregistenlif you window wereto hand in the codefrom the disassembly I suspectthat eventhe mostdim-witted unchanged, teacherwould noticethat somethingwasamiss.Second,the codedisplayedin the DisassemblyListing window doesnot haveany goto labels,and you will find it to be a significantchallengeto correctlymove the locationof the codeproducedby the PICC Lite compilerto the locationsrequiredfor your application. Chancesare it will take more time and effort than if wereto do it yoursell Finally,the worst thing that couldhappenis that you correctlylabel the registers and addcorrectgoto labels,and then your teacheris so impressedby your work that you are askedto explain to the whole classhow the codeworks.If you're having createa problemssolvingan applicationin assembler, program the PICC Lite compiler C and lun it through to seehow a professionalwould codethe application. But remember,it's in your bestinterestto take what you learnfrom the DisassemblyListing and applyit to your application,rather than trying to usethe code that'sdisDlaved.

" 5 u ri tc h " ExFer im ent 73- lm pl e m e n ti n gth e f S t at em entin H s s e m b l gL a n g u a g e In this experiment,I would like to showhow the C switchstatementcanbe implementedin assembler: ( (variable) switch // value lo be testeal case 2: nvaliable == 2n to E.ecute if // Statenents the "switeh" Statenent breakr // Exit cas€ 23: == 23 if, 'variable to Execule // statenents br€akt

If askedwhen I first learnedto program,I like to reply that it hasbeengoingon for 25 yearsnow.Theimplication is not that I am somewhatdim, but insteadthat thereare so many differentwaysto solveprogramming problems.I bring this up becausethe codefor this expedment,which waswdtten after the codefor the followingexperiment,is a lot mole efficient(i.e., smaller)than the codein the following experiment. Logically,the programsshouldbecomemore sophisticatedandefficientasyou progressthroughthe book.I wantedto illustratea particularpoint, so I placedthis more efficientprogrambeforethe lessefficientone that followsit.

//

//

Statenenls b!eaki default: statenents "variabl€ ]

//

Uo Execute

if

nvariable

== 47

l= 0 oi 47 // "variabl€" != 0" and to Execute if, "variable t= 47" hctiws

There are several ways in which the switch and case statementscould be implemented in this block of code to execute specific code if the contents of a variable match a specific value, but for this experiment, I will focus on the general casecode. One way to implement this function is with multiple comparisons.lf this were to be written in a language

S e c t i o nN i n e A s s e m bI y L a n g u a g e R e s o u r c e R o u t i n e s

191

with an "if then goto" statement,the switchstatement could be implemented as: (2 == Variabl€) if th€n == ?LraE gwitch CaEe StaEenelts to tlr.ecute lf goto gwitcbDone

{J

// //

ct

Not2: (23 == Vrriabl€) if th€! // == s€coaal Snitch Case // Staldl€rta to Execute if goto swilchlrone Not2 3: ({7 == Variable) tf th€n // == Thirit S:nitch Caa€ // gtaldlellta to Execute if goto switclDone Not{7: - Stat€arenlB // trD€faulli to rrvari.rbl€ != 2' anal

c

E o

.p

(s

.tJ

q

"q ()

{J ''.1

B

q

U

c,

rrvariabl€

!= 23'

nvariable

!= 47tr

gotso Nots2 "Variable

goto

| I

golo

c

trvariabl€

Executse

movf, r.or1!r

variab1e, 2

9{

X

rd

{t

if

,

"tf

(2 == variable) goto Not2r

btfaa sTAlt'os, z gtoto Not2 'varia.b16 ^ 2n equal to Ex€cute // Staletrents tf z€lo switchDone "o"o Not2: xorlrc 23^2 , W R E G= ( W R E G ^ 2 l ^ ( 2 3

^ 2)

t = W R E G ^ 2 3 ^ 2 ^ 2

t gTATUg, Z btfaa goto Not23 // gtelen€nts to tir.ecute

goto switchDon€ Not23: r.orLlr 47 ^ 23

L9z

l-

23n atd

^ Hnoi

23 (B€cauae2

"Valiabl€

if

-=

23

, wREc = (WREG ^ 23) ^ lA7 ^ 23) , = W R E G ^ 4 7 ^ 2 3 ^ 2 3 , = vlR.EG ^ 47 (Becatnae 23 ^ 2 3 = 0 )

bbfa8 STATUS, Z golo !bt{? // Stalen€nla to E lecule grditclrDone goto No!{t: - Stsatenenls // "Defaultrr "Vari.rbl€ t= 2" aDil "valiable

{?tr

naamPKIJED 2 LED"

PICkit

1 starEer

Lf

lo

"variabf,e

Execute

== {7

if,

hit

copies r This program allrectly the op€ratio! CPKLED.c antl Elaaheg the I LEDa oa the PICkil , 1 alarter LLt in Sequenco. i Hartlwar€ llotses: PIC16F68{ rutlDing at 4 llllz Usltrg t Clock Exterttal Resel ia Ua€fl t Circuit Runa oa PICkit 1 Etart€r r

!t

.Fl (,

=-

!=

This method of implementing the switch statement in assembleris quite efficient and easyto code,asI show in the code for this experiment, asmPKLED Z.asm.In this codeI havetried, asmuch aspossible,to dfuectlyconvert the highJevel statementsof cPKLEN.c to assemblylanguagestatements: lit].e Ruaning

Not{?

This isn't a terrible baseto work from, but we can do better.The secretto doingbetter is to load the vari, able into the WREG and then compare its contents usingthe xorlw instruction repeatedly.Take advantage of the MPASMTMassemblerbuilt-in calculatorand XOR the valueto be testedwith the Dreviousvalue.Bv doingthis.the previousXORed valui in theWREG is returned to the original state and then XORed with the new value.To showyou what I mean,I canconsider the if equivalent to the switch statement as:

c

t{

23

SwitchDoE€:

t-

c,

-=

anat

1Y1

1J

No!23

,'variable

thea

IJ

== 2'

rvaliabl€ SwitchDone:

t Original r inl

i,

the

rnternal

Lits

Coale: J, kt

r nain ( ) t t r

t PORTA

= 0t

t

ANSEIJ

,

k -

=

0i

0;

// //

Turn Tufi

//

starts

t //

== 1) wbile(l IrooD Eorever

r //

sirnDle

, ll t t t t t r r i i i t t i r , t

(k) t alritch geLecL Whicb LED to DieDlay caae 0: PORTA = 0b010000, TRISA = 0b001111, breah, caa€ 13 PORTA = 0b100000t TRrgA - 0b001111t breakt caae 2r PORTA = 0b010000t TRISA = 0b101011t braakt caae 3: PORTA = 0b000100t TRISA - 0b101011, breaki

t t r t r r i i

PORIA = TRISA = breakt case 5: PORTA = TRISA = breekt cese 5:

off off a!

Cdrlraratoig A.Dc LED 0

f,or (i = 0r t < 255r i++) Etelay IJooD for (j - 0r j < 129r j++)t

0b100000, 0b011011;

0b000100; 0b011011t

l , e 3 P I C @l l C U E x p e n i m e n t s f o n t h e E v i l

6enius

of

= 0b000100t = 0b111001t

r r i ; i , i r

PORTA TRISA br€aki caa6 7t PORTA TRISA breelr // l

, //

k E ( k + 1 ) ? 8 t IDcr@ent k lrithi!

, ,

l )

//

= 0b000010, = 0b111001,

of

& -INTOSCIO

Varlabl€g CBI,oCK 0:.2 0 Dlay Actj.veBj.t E![DC r

r Recoril

Bil

tsb6 Activ€

Turrr

,

SetuD TRIS for Nd.t Disglay

mov$f goto

II{DF LEDIron€

o

EoD

For

t

Cl.lCONo gTAfUS, RPo tt{SEL ^ 0x80 srATus, RPo

t All

I/O

Blts

to

Trr/D2: xorl$ btfss

2 ^ L gTAtgg,

golo movltp novfif rnovlw

Trt'D3 8'010000, PORTA 8,101011,

rtrovwf goto

INDF IJEDltole

BitB

Digital

a!€

AcElv€BLt

r gtalt

novlw

TRISA

novl "f

FSR

r PoLnl FgR to TRISA fo! raat TRrsa try)alating t

Loo93

i

D].ay

btfss goto tlecfaz goto clrf

sT ms, S-2 Dlay, t S-{ Dlay

, Dlsplay

i i

i

-1

rdith

Returl Delay High

8 Bits

D€cr€eeat conlenta 256'* t i

z

clrr' edld].w

-1

btfaa goto al€cfaz groto

sTATus, z $-2 Dley, f. S-4

Dovf

ActivcBit,

t R€Deal i

o

th€

Ft F.

Rep€at

Tuln

on D1

getuD

fnIS for Dj.aDlay

, R€D€a!

for

D6Lay

tlre of VIREG

R€p6al Again 400 ms total

f,or Delay

255x

Bit

movlrf grolo T4fD5: xorlv btfa8 golo lrovlrd lrovwf movlw movwf goto

th€ of WREG

t Loadl the

FiniEhed,

t DisDlay

i

the

tr.|

R€9eat

(^,

D2?

Turn

I

on D2

t S€luD TRIS for Next Dis9Lay

8'000100' PORIIA 8'101011'

r DIaDIay

r Tuln t

getup

MDF LEDDone

the

4

ro

ReDeet

r Finiahedl,

3 ^ 2 Sf[lTUg, z Trl'D{

{ ^ 3 grATItg,

5 rt

Z

NdrE

TryD{: ,ror1w btfaa goto novlw ovnf rovltr

3 o

Dl?

D3?

o

on D3 IRIS f,or Dl.aDlay

t Finishedl, i

DigPlay

i

Turn

,

getuD

th€

Q

ReDeat

{

D{?

F.

rf

z

TrtDs B'100O00' PORTA 8'011011' INDF IiEDDoue

o

on D{

TRIS for NexE Diaplay

t Finlahetl,

the

Rep€at

efter

255x

r Decra€nl coDt€rrta , 256x

rr

D0

ll6re

t

Off lovwf goto

clrf

clrf clrrl' aaLllw

8'100000' PORITA 8,001111, MDF IiEDDoa€

lrov1w movrrf, lrovlw

ICD Delntg

r hitialize , Turn off

PORTI 7

16

on D0

, Einisb€al,

1 ^ 0 STATUS, z TrfrD2

movlrf goto

Tr,yD3 ! xorlw btsfaa goto

PAGE uailline

clrf novlv coqraralors novn"f baf clrf bcf

i

Next

_cowrrc _ltllEN_oFF & *IEgo_oFF & _BoD_oFF & _CPD_OF! & _CP-O!F & -!|CLRE_ON & _PIIRTE_ON &

or9

8'010000' PORTA 8,001111,

novlw rovlrf, movlw

'IST R=DEC INCLI'DE nD15f 58{. iDc"

t

movlw novwf fiovlw

TryDl: r
// €lihw Enal CPKLED

liEfke P..tlko 0i1.11.28

_WDI*OFF

, Start

0-7

t t t

E4 X

D0

0 slATUg, z EryD].

hctL$3

reig€

r'ith

*o!lw btfBs goto

Nlrmber

Trl'D5 3 xollw blfBs goto movl$ novlr'f, movlw movlrf goto

5 ^ 4 z sfATlrs, TryD6 8'000100' PORTA B,01101f INDtr rrEDDone

t DisDlay

d

i

Turn

i

getuD !'Rrg for N€trts DiEI'laY

MDF LEDDone

p, ct

on D5

t Finisheil, r DIaDIay

5^5 z Sf!l!!gs, llryDT 8'000100' PORIIA B'11100f

CN

D5?

lhe

o 3 o p

R€96a1 D6?

a+

on D5

i

fuln

i

S€EuD TRIS f,o! Next Dlat)lay

t

FiniEheal,

lhe

RsD€al

S e c t i oN n i n e A s s e m b l yL a n g u a g eR e s o u r c e R o u t i n e s

193

TryDT : xorL$ btsfaa goEo ovht monwf novl$ novwf goro

,

7 ^ 5 STAllrUS, IJEDDone

PORTA B' 111001'

t Turn

Finiahetl,

IJEDI'ON€:

andlw

7

movwf

Acliv6Bits

qoro

LooP

on D7

r geluD TRIS fo! N€xl DiaDlay

I![DF LEDDon€

AcliveEiE,

D7?

Z

B'000010,

Ldcf

DisDIay

the

ReDeat

FiniEh€d DisDlayingr LED Inclelent the Active IED Ke€p witshin rang€ of

o-7 i

RepeaE

end

Thereis one lastpoint I would like to make about aSmPKLED2.asm,andthat is how I wasable to quickly changethe valuesof the TRISA register.In the code,you seethat I loadedthe FSR registerwith the addressof TRISA, and when I had to changethe value of TRISA, I simplywrite to the registerpointedto by the FsR.Another way of implementingthis code would be to changethe bank and write directly to TRISA (without involving the FSR register), using the following code: lrovlw

NewPORTAValue

r WrLte value

nrovwf nrovlw

PoR!!A NevrTRISAValue

,

bsf noverf

STATUS, RPo rRISA ^ 0x080

i i

bcf

SfATuS,

i

RPo

the

nevr PORTA

SetuD TRISA f,or tshe Nexts DispIBy Ex€culs in Page 1 Sto:.e lhe New TRISA VaLue Return E:.eculion to Page 2

Experiment 7U-Defines and it behavessimilarlyto the C languagedefine.That "String" is substituted is,when"Label" is encountered, in with and any argumentsput into the string.The stringsubstitutionprovidedby the #definedirective differsfrom the operationof a macroin the scopeof the substitution.The #definesubstitutesa stdng on a line of assemblylanguagecode,whereasa macrosubstitutesthe entire line (andmaybeaddsadditional lines).

{t

c

,t{

{+.{ 0,

n I, qr f* {J

fr

0l H

. r-! ( r

CI g-. t\,

n

If you haveworked throughall the experimentsin the previoussection,you will havenoticedthat accessing UO pins in assemblylanguagecan be somewhatawkward due to the needto specifyboth the port and the bit numberof the pin in the bit inshuctions.As you start programming your o\an applications,you will discovercaseswhereyou mix up which port is usedwith which pin; the program will not work and the problem will not be easilyfound by readingthroughthe program.You will be able to find the problem by carefully sirnulatingthe applicationand watchingits operation, but there is an easierway to avoid the problem all together.Insteadof associating a pin with an IiO port register for the bit operations,you can declare them together using the #define directive. The format of the #define directive is: +alefine

Label[

(argullenl

[,...1)

]

Strins

The most common use of the #define directive in PIC miuocontroller applicationsis for the combining the port and bit numberfor a specificpin. For example,if you wantedto declareRA3 asan LCD's clock (E) pin, you couldusethe statement: *dlefine

LCDE PORTA, 3

Now,whenthe label LCDE is encountered,asin the bit statement: baf

IJCDE

the string"PORTA,3" will be substitutedinto the instruction. To demonstratethe useof the #definefor port pins, I createdthe asmPKLED.asm, which is a "port" (or languagetranslation)of cPKLED.cand cyclesthrough the eisht LEDS of the PICkit 1 starterkit.

kl L9s

l , 2 l P I C @l l C U E x p e ri m e n t s f o r

the Evil

6enius

litl€ I,EDN

"asnPKLED

-

PICkil

1 atarter

kit

r r i

This program cogi€s th6 anfl Fla6hea the 8 IiEDa 1 start€r on the PICkit

i , i i ,

Hartlware Notea: ruDains PIC15r58{ al 4 Mlz Using In!6rna1 Clock Ext€rnal Reaot ia Usefl 1 start6! Clrcult Runa oD PICkit

IJED DEfi'tEA: ; DoAnotl€ *alefin€ *al€fLne Docathoalo DlAnoA€ #al€fln€ *alefi.ne Dlcatshotle D2Anoal€ #a16fitre D2catbode *al6fLne D3Anoal€ *defin6 D3cathode *alefin6 D4anoale #alefin6 D4cathoale *alefin€ D5anod6 *ilefine Dscathodle *alefine D6anod€ *alefia€ D6cethoale *d€fine DTAnoale *il€fine DTcelbod€ *ilefine i t t

functioa kit

of

cPKrrED. e

g€qu€nce.

ln

kit

lilyke Pretlko 04.10.0'l LIST R=DEC INCLUDE "p15f,58{,

inc"

& _BOD_OrE & _colIFIG _FCUEN_OFF & _rEgO_OlF _CPD_OFI'& _CP_OFF & _!!cIrRE_O!{ & _PIIRTE_ON & _!itDT_oPt' & _rNToscro valiableB CBI,oCK 0x20 Dlay Activ€Bit EiNDC

,

the

Activ€

TryDl: aaltlln btfBa goto bsf

-1 STAfUS, z TryDz STATUS, RPo

bsf

Doaloale

bBf bcf bcf bcf bsf bcf goto

Docathoale DlAnode Dlcathotla STATUS, RPo Dlt'loil€ Dlcatboal€ IJEDDIay

!!zr/D2, aaLllw btf56 gotso bsf bsf

-1 STATug, z Trl'D3 STATUS, RPo DlA.aoale

baf bcf, bcf, bcf baf bcf goto

Dlcethod€ D2nnoale D2calhodle SfATUS, RPo D2}Ilodle D2calhoal6 I.EDDlay

baf bcf bcf bcf bsf bcf goto

0

DOD

,

clrf

PORTA

rnovhr rtovwf b6f cLrf bcf

7 C!{CONo STATUS, RPo ANSEL ^ 0x80 sTATuS, RPo

clrf

lcliveBit

Eor

Loop !

CoaE)araEorB

r A11 Bits

ar€

iacf

Actlv€Dit,

rd

aaLlfuc blfaa golo bsf bEf

-1 STAqrS, z TrJ'D1 STATUS, RPo DTAnod€

lrlth

I/O

Bita

D0

i i

Stalt

t tur!

tql

X

D0 IrEDa

b r rlaiahefl,

o

r-l

Repeat

; DiaDlay

i

D1?

t!ur! olF DisDlayeal

r EnabLe

D2cathotle D3Anotle D3cathotle STATUS, RPO D3Anoal€ D3cathod€ IJEDDI8y

3 o p

rt

D0 IJEDa

--l t Finisheal,

|'F

R€Deat D2?

U

OFF Previously t furE LED DiEDlayeal r Enable

o

D0 I.EDg

Hh

t-r. r-t

i

D3?

Turn orF Dis91alreal

t Enable

r0 m

Repeal

r rlaiab€al, r DIapIay

-1 STATUS, z rrylx STATUS. RPO D2t'lode

F.

Previoualy LED

, Diaplay

P!€vioualy r,ED

D0 IrEDa

t fidiah€il,

with

r DiaDlay

TryD{ ! aalillw btfsE golo baf bsf

ReDeat

STAITUS. Z ErfzDs sTATug, RPo D3Anod€

bsf bcf bsf bcf baf bct goto

D3celboale D{Anoale D{Calhodle RPo STlrUS, D{Anofle D4cathotle TJEDDIay

D0

OFF Pr€viously

TryD5: aalallrd btfaa goto bsf

D4?

-1

Digital

Retura llere aft€r D6lay Loail the Bit Ni'mbe!

i

LED

ICD D6bug

r hitialize to off , TurD off

r glarts

r E[ab1€

Bit

PAGE Malnlin€ org

DTcalhodle DoAnoile Docalhod€ RPo STlrUS, Dohodl€ Docathodle l,EDDlay

TryD3 | ailtlllr btfsa golo baf baf

t

r Recoral

baf bef bcf bcf, b8f bcf, goto

the

4 5 5 { 4 2 2 1l 5 2 2 5 2 1 1 2

PORTA. PoRTA, PoRTA, PoRTA. PORTA, PoRTA, PORIA, PoRTA, PORTA, PORTA, PORTA, PoRTA, PORTA, PoRfA, IORTA, PORTA,

DisDlay€dl

Rutralng

-1 STAfI'S, z TryDS

r |IurD OFF Pr€vi.oual.y DiaDlayetl LED r Enabl€

i

Finish€dl,

i

Display

D0 LEDg

R€Deat D5?

STATUS, RPo

S e c t i o nN i n e A s s e n b l y L a n g u a g e R e s o u r c e R o u t i n e s

195

bsf

D{$rotle

bgf bcf bcf

D4Catshoale D5Anode D5Calbotle STATUS, RPO DsAnoale D5CaEhoale IJEDDIay

bsf bcf goto

Tura OfE Pr€viouBly Diaplayeal LED Enabl€

incf

ActiveBl.t,

enalfto

7

novwf

ActiveBil

gotso

LooD

!t

D0 IiEDs

Flnlshedl,

, i

IncrerneD! lh€ Active IJED Keeg Within range of o-7

; ReDeal

Repeat €Dit

TryDS: aaldlftt btf,aa groEo baf, baf, baf bcf bcf bsf bcf golo TryDT: atlalllt btfaa groEo bsf b6f bsf bcf bcf

ul () .Fl

t+{

o

o I

I

qr

t-

bsf goto IJEDDIay: clrf cl!!t atlillw btfEa goco dl€cf6z goro clrf

Dlsplay STATUS, Z Tt!'D1 STATUS, RPo D5Anodl6

ENAbIE DO IJEDA

Eioiahetl,

R€peat

Display STATUS, IJEDDIay STATUS, D6Arode

RPO luan OFF Pr€viouBly DiEDlayeat IjED Enable

t

D0 IEDE

Finlah€al,

Dlay

Eigh

-1

Declqrenl contenta 256r.

Dlay,

D7?

Z

DScathod€ DTenoale DTCatbode STATUS, RPO D7Alodle DTCathoAe IJEDDIay

sTATtts,

z f

I

Repeat

Re9€a!

Bita

for

lr€Iay

the of WRIG

255x

s - 4 DIay

Re9eat AgaLa 400 ma De].ay

fo!

STATUS, Z

Decremenl th6 contenta of, WREC 255x

DIay,

ReDeal

f

Chancesare that if you were to codethis application (with six I/O port register writes for eachof the eight LEDs) without the use of the #define directive for the different port bits, you would make several mistakes.The #define directive simplifies tedious code operations such asthe onesrequired for this application.

Turn OFF Plevioualy Dl.aDlay€al IIED

D5Cathodle D6Aaod6 DSCatlrod€ sTlIus, RPo D5AIlodl€ DSCalbofle LEDDlry

c1let aaltllrt b!faa goto alecfez go!o

D5?

255r.

-

I don't want to leaveyou with the impressionthat the #define directive is only for simplifying I/O pin accesses; like the C languagedefine, it can be used asa shorthand way of adding constant arithmetic operations to the application without having to type them repeatedly.Addirionally, bit-flag variables can be declaredusing #define directiveg in the sameway the I/O port bits are declaredin this application. Remember that like rnacros,#define substitutions take place belore the assemblystep.As far asthe assembleris concemed,the strings are constant valueswhen it executes.#definescan also be usedfor defining strings that are usedto control the operation of the code build (This will be discussedin more detail in the next experiment). But the most common define is created by the MPLAB IDE to specifywhich PIC MCU part number information is to be usedby the assembler. As a final point, you'll seethat I implemented the C switch equivalent code in a different manner than in the previous experiment.In this experiment,I knew that the valuesto turn on eachLED are arranged sequentially.So rather than implementing a generalcasesolution 1othe problern, I took advantageof being able to decrementthe value by one for eachLED and finally stopping and displaying the LED when the result is zero. Remember that there is alwaysmore than one way to skin a cat.

.tJ

0,

d 'rl

f{ (,

O{

X

kr 196

l , e 3 P I C @l l C U E x p e r i m e n t s f o r

the Evil

Genius

14 LJ

Experiment 75-EonditionalHssemblg *atefine novf €Ise nov].w €ratif

The exampleapplicationshownin the previousexperiment wasa pretty clumsypieceof code.The task of lightingeachof the eightLEDS on the PICkit 1 starter kit is not somethingthat lendsitself to algorithmicprogramming.Although the codefor eachLED is the same,but there is no consistency betweenpairs,which necessitateswriting code for eachLED. The final result is an applicationthat is quite long and cumbersome. What is neededis a way to minimizethe development effort.The taskof lightingeachLED in sequenceis not a problemthat is easilyaddressed by usinga single previous LED and turning data table.Tuming off the on the next one,asI havedonehere,is not a terribly inefficientway of implementingthe application. The problem rather is how to efficiently code the applicatlon. A potentialsolutionto the problemis to usethe conditional assemblydirectives built into MPASM assembler.These directivesallow you to selectwhich codeis to be assembled or evento createcodealgorithmicallythat canbe assembled into the application. In the interestof clarity,I mustpoint out that these directivesexecutebeforethe codeis assembledand are usedto selectwhichcodeis and isn't part of the assembly. Although conditionalassemblyis not a critical concept,it is somethingthat canmakeyour life quite a bit easierand allow you to producehigherquality code. The basicconditional assemblydirectives are ifdef, ifndef. else.and endif.The ifdef and ifndef directives passany statementsthat follow them if the specified #definedlabel is present.Theelsedirectiveprovides alternativecode,and the endif directiveindicatesthat the ifdeflifndef test is complete.I commonly use these directiveswith the Debug #defineto avoidcodethat will not operateproperlyin the MPLAB IDE simulator. For examDle:

D€bug D€bug ADREgH, Ttr 0x088

4V r IJoatl in ADC ResuLts r In Simulator Readl r sillulaleal

ffi

will return 0x088in WREG if Debug hasbeen #defined,skippingover an invalid registeraccess. When usingifdef and"ifndef' to add and take away instructions to avoid problems simulating the application, you shouldmake surethat both pathshavethe samenumberof instructionsand executein the same number of instruction cycles.This will ensurethe appli cation will executethe sameway in the simulator and onceit is bumed into a chip. As I indicatedin the previousexperimenta common declared#defineby MPLAB IDE is the PIC MCU part number, which consistsof two underscore charactersfollowedby the part number.For example, the PIC16F684usedin this book would havethe #define_16F684.In your applicationyou can testfor this define using the ifdef or ifndef directives.This capability is useful in caseswhere different PIC microcontrollers might be usedin the sameapplication.For example,whenyou are designinga product,you may want to usea part that hasFlashand can be easily reprogrammed(like the PIC16F684), but there may be programmable (OTP) part that can a cheaperone-time perform the samefunctions at a fraction of the costs.A conditionalassernblystatementwill allow you to use the samesourcecodefor both PIC MCU part numbers,with the only differencebeingthe numbersspecific to the different chips. expressioncan be evaluatedby A single-comparison the if directive,which alsousesthe elseand endif directives.You alsocandefinenumericvariablesin your application that exec$e before application assembly. For example,a variablei couldbe declaredusingthe variabledirective,and later in the application,it could be testedagainstdifferentvalues:

fn 6

r*lr,,

|h,

.i:ft {f,f

It)

H

t"{rd ,*.i

variable

i

L-n

,i , , " b8f PORTA. 5 eIa€ bsf PORTA, 0 i = i + 2 enalif

S e c t i o nN i n e A s s e m b l y L a n g u a g e R e s o u r c e R o u t i n e s

L97

Labelsdeclaredusingthe variabledirectivearejust that-labels.To changethe valueof a variable,it hasto be placedin the first columnof the applicationsource codeasI havedonein the previoussnippet. The final conditional-assembly directivesare the while and wend directives,which allow you to place the samecoderepeatedlyin an application.Theformat of theseinstructionsshouldnot be surprising;if you wantedto put in four nop instructions, you could use the directives: variabl€

CD2cathoal€ CD3anoale CD3cathoal€ CD4Anoale CD4cathoale CDsAnoale CD5cathoal6 CDSAnoale CD6cathotle cDTArode cDTcathode

i ,

i

variables variable LEDCount cBr.ocK 0x20 Dlay AcliveBi! ENDC r

r

rrasncond

-

Coflalitional

Thia plograln takes aalvantage of the conalilional assernbly features of !4PAS!I and instead of repeating block of coale seven tines that cycles the I,EDS on the PICkil 1 starter kit, !h€ coale is put in algoritlllnicall"y.

t , r r ,

Harflcrare Notes: PIC15F584 rulltling at 4 MHz Using hLertral Clock External Reset is UBeal Circuit Runs on PICki! 1 stalter

LED Defines: r CD0Anodl6 EQU CDocathod€ EQU CDlanotle EQU CDlcathoal€ EQU CD2Anoale EQU

4 5 5 4 4

the

to

Display

Activ€

Bit

asniPKLED

nop

t

cl.!f

r hitialize off off t rurn

Conparators

r AII

are

the

kit

novl"w novwf baf clrf bcf

7 Cr?rCONo STATUS, RPo ANSEL ^ 0x80 STATUS, RPo

clrf

Acti.veBit

incf

a

rr

lrhil.e lEDCoun! < -1 adillw btfas STATUS, soto $ + 10 baf STATUS, if 0 == LEDCount bsf bsf, else bsf bsf enali f bcf bcf bcf bsf bcf goto IrEDCount €ntlw

ICD Debug r/O

Bits

Return Delay t LoadMe i

ActiveBit,

!'or

r starl

IJoop:

Asaenibly"

r t r r r r r

1ge

of

t OnLy 7 B i t s

t Recolal

Var?Value

This last directiveprobablyseemssomewhatesoteric,but it allowsyou accessindividuallabelsasif they werearrayelements.I havedoneexactlythat in asmCond.asm, which is a rewrite of the sequencing LED applicationand usesthe while,il and #v directivesdiscussed hereto producethe identicalcodeto the previousexperiment'sasmPKLED.asm), but it avoidsthe needto put in the samecoderepeatedly. titl€

PAGE Uainline

= 0

org

Va!#v(i)Value

the assemblerwould processthe instruction: movf

l,lyke Predlko 0{.10.04

FCMEN OFF & IESO OFE & _BOD_OFF & -CONFIG -CPD OFF & CP O!'F & _IICIJRE_ON & _PWRTE_ON & ,litDt oFl' & INTOSCIO

When usingthe while directiveto implementmultiple instancesof applicationcode,you canusea littleknown directive,which is in the format #v(expr)and insertsthe nume c valueof expr into the application code.For example,if the variablei had the valueof 7 andthe statement: novf

2 2 4 5 2 2 5 2 1 1 2

LIST R=DEC INCIUDE "p15f684.inc"

Counter , hitialize i Repeat 4x t Put j"n notr> Counter i Inc!€nent t IJooP Enal

while i < 4 nop i = i + 1

EQU EQU EQU EQU EQU EQU EQU EQU EQU EQU Eou

with

Bits

Diglital

D0

Here Bit

after Nllnber

r Repeat the coale 8x Bi.t Cou[t i Decrement

rurn off, D7 if D0 B€ing turn€d on PORTA, CDTanoal€ i Turn OFF PreviousLy Display€al LED PORTA, CDTcathoale

TRISA TRISA

^ 0x80. ^ 0x80.

,

cD#v(IJEDcount-1).eloale cD#v ( lEDcount - 1) cathode

^ 0n80, cD*v( LEDcount )Anoate ; Enable LED,E I/O Pi[a TRISA ^ 0r.80, CD#v(LEDcour!)Cathoale STATUS, RPo PORTA, CD*v (lEDcount. )Anoale PORIA. CD*v (LEDCount ) Cathoale IrEDDLay Repeat ; Finishedl, += ! , Do the Next, LED TRISA

l , a 3 P I C o l ' l C UE x p e r i m e n t s f o n t h e E v i l

6enius

to

IJEDDIAY: clrf clrw addlw

, tligh

Dlay -1

I

Bits

Decrdn€n! of WREG 255'*

gTATgS,

btfss goto dlecfsz goto clrf

l-2 Dla]', S-4 DIay

clrw afltllw

-1

blfaE golo flecfaz goto

ST.I|luS, S-2 D].ay, f s-{

incf

AcliveBi!,

f

R€p€a!

for the

Decrelrenu of VIREG

w

;

aaaU.w

coutents

255x

Re9oat Again ma Delay

Rep€at

DeLay

the

for

-

{00

contenla

255x

rnclernent the Activo IJED Keep wilhin lang€ of 0-7

ActlveBit

goro

IJooD

,

Re9eat

enal

When you look throughthe code,you'll seethat I have replacedthe pin defineswith equates.This was donebecausethe #v(expr)directivecannotbe used with other dtectives. As I have emphasized,the previous and the next experiments'directives exec'rlebefore Only one the application'sinstructionsare assembled. passis madeto the preprocessor that executesthe directives,and if any directivesare changedand require additional execution,the application will fail. I did so with an When I createdasmPKLED.asm, eyetoward repeatingit with conditionalassembly statements, but it is still not that inefficientin termsof execution and program size.The problem with asmPKLED.asmis in its creation;althoughthe instructions for eachLED can be cut and pasted,I found it a chore to changewhich pin definesare usedfor eachLED (and I madetwo mistakes).By usingthe while directive and other conditionalassemblydirectives,I eliminatedthe task of repeatingthe sameinstructionsover and over andminimizedthe opportunityfor errorsin the application.This is really the major advantageof usingconditionalassemblydirectives:Theyhelp you minimizeopportunitiesfor makingmistakesin your aoolication.

k*t

n4

?-1;

r*

=,1 L'* :

,ar: :: .:. i:J

ExFeriment 76-Macros

i.t:

The MacroParameteris a singlestringor multiple stringsthat are substitutedinto the macro at assembly time.For example,if a macrowasrequiredto load WREG with a numericvaluedividedby two,the macrocouldbe definedas: novhrDiv2 tnovlw endm

The next level of codesubstitutionafter the #define,in MPASM assemblylanguage,is the macro.Macros consistof instructionstatementsthat are insertedinto an applicationalongwith the other directiveswhen the preprocessor is active.Although thereis not one allpurposemacrothat canbe usedto illustratethe concept,macroscan greatlysimplifyyour application programming.This is especiallytrue if you take advantage of the #define and conditional assemblydirectives presentedin the previousexperiments. The format for declaringa macrois quite sirnple: llacroName maclo i llacro coale enalll

}lacfoParaneterl,...

I

llacro Div2value Div2value / 2

If the macrowasinvokedwith a Div2Valueof 47, the followingcodewould be insertedinto the program: novlw

47

/

2

Macroscantake advantageof the conditional and surprisassemblydirectivesof MPASM assembler, created from them functions can be ingly sophisticated asI will show in this experiment. The reasonsfor usingmacrosin your application includethe following: . .

Minimizing programkeying Reducingprogram executiontime

.

Minimizing program .hexfile size Simplifyingthe sourcecode

.

S e c t i o nN i n e A s s e m b l y L a n g u a g e R e s o u r c e R o u t i n e s

199

. r .

Providingopportunity for optionally compiled functions Providingadvancedbuild-time options Simplifyingthe effort required by new programmersto createtheir own assemblylanguageprograms

Functions and subroutinescan be written as macros, and,dependingon their size and the nurnber of times they are accessed, they can decreasethe programexecution time, complexity,and size.Macros can be added to the program, in the sameway a subroutine or function call is added.Themacroavoidsthe overheadof the calVretum instructions,and placing parametersin subroutine- or function-specific variables can reduce both the total spaceand variable requirements of an application.They also provide the assemblylanguage code with variably added functions,and they do so without having to savethe functions in a library and hope that they will not be linked into the final application.

(t)

o l{

U d

E I

One importantnote to newcomersin the programming world about the use of macros:Although you may not have the abilities (yet) to implement macros for simplifyingyour programmingworkload,I'm sure you can identify situations where assemblylanguage programming seemsparticularly dfficult and, therefore, would benefit from a macro.One such example, which I addressin asmMacro.asm, is the if decision structurein PIC MCU assembler. In this exneriment-I havecreateda macrothat usescondilionalissembly directivesto insert the appropdate four-instruction templatecode(presentedin Section8) for a conditionaljump basedon two variablevalues.

\o t\

E

tflrla a9plicalioa alenonstrat€E the Mecro lrhich co4Dar€s lwo valu€a aaal execul€E according sDecif ietl coaalilion.

'ifgo!o"

IjIST R=DEC INCLT DE np15f

r.l

X

'lfgoto,

Dernonstrate

Uyke Prealko 0{.09.1?

'r{

P-.

-

Harahra!€ Not€6: PIC15F68{ ruEing al { IqHz in Re6€t ia lieal alirectly to vcc PuLLup/Prograrming Earalwar€

g (t

$

"asrdtacro

the

litle

r

Variabl€a CBIJoCK0x20

I, J

58{.

idcrl

to

Simulator vie

the

tlaclo i ifgolo ttacro Ver1, C6p, (1 CdE) 0) if (0 Corm 1) if movf Var1, !t aubwf var2, !t gTATUg, Z btf8a €1ae (1 coiq) 1) if novf V€,E2, \r autMf Var1, w btfsc sTATus, c elge novf Var1, w aubwf Var2, rd btfss sTATus, c €ntlif €nalif 6Lse i.f (0 corll) 1) (1 Cofqr 1 ) if novf Var1, !t aubwf var2, w btf,Ec STAIUS, elae novf Vat2, w aubwf, Va!l, w btf,sa SfATUg, eDdif elae (1 Co|sp 1) if movf Var2, w aubirrf var1, w btsfac STATOS, €1a€ 6r!0r ltahnowa ,,if,n endif endif entlif goto Dest endm org nop

Va!2, t

ch€ch

i

Elae

nl=n /t>n

n>n/r>=fl

; check

for

"<"/"<="

Conili.tlor^

15 i 20 j j,

, Requiledl

for

t Ge!

Valuea

i,

>,

no9 ifgoto

i,

>=,

nop if,goto

j,

<,

DO9 ifgolo

j,

<=,

L,

ErrorDOa€

IoD ifgoto

i,

==,

j,

E!rorDon€

i,

novnf

j i,

j,

E!rorDon6

i,

t

j,

geE Equala fo! Equels Teat

ErlorDon€

EO9

f.1

l,e3 PICo llCu Expeniments for

ICD2

ErrorDone

w

l-,

!|PIA8

EtlolDou€

ifgoto

Dovf

!!eal

ENDC

200

/\>=t

0

rnovlw trovwf movlw alovwf

ifgoto

Deat fo!

the Evil

Genius

Not

i,

ifgoto

==,

j,

coodDone

Codte Shoul.tl be llele

EtlolDone: goEo

NEVER

EfrolDone CouLdl shouLal He!e

GooalDo[e: goto

shouLal be rnatsch, i rrE) to PloDer Enal

Enal

GooalDone

enit

The ifgoto macro in asmMacrois useful to people other than new PIC MCU assemblylanguageprogrammers.I shouldpoint out that the preprocessorin MPASM assemblerwill not recognizethe difference between variable labels and constant values.This is unfortunatebecauseyou will haveto modify this macroif you want to perfom a conditionaljump basedon the contentsof a variableand a constant.The background for the changesrequired to modify this macro to support constant valuescan be found in the "ConditionalExecution"exDerimentin Section8.

95X 6J

ts:r{ iU

@

tgx

abIes utith Experiment77-16-Bit ValuesA/ari Flddition,Subtraction,and Eomparison 0x01234would be displayedin memory as"3412," which requires you mentally to rearrange the bytes. is not requiredin the This mentalrearrangement MPLAB IDE simulator.You candisplay16-bitdata in MPLAB IDE by settingthe propertiesof the Watch window to 16-bitdata,in little endianor big endian formats. With the availability of the cblock directive, you can declarethesamel6-bitvariableas. I find that whenI am doing actualPIC microcontroller eight-bitvaluesare simplynot enough. applications, Sixteen-bitvariablesprovideyou with a significant amountof additionalprogrammingflexibility in a variety of differentareagincludingthe creationand processingof data.Programmingfor 16-bitvariablesis not beyondyour capabilitiesif you havebeenfollowing along.In fact,you will find that 16-bitvariablesare not that hard to work with, especiallyif you follow the rulesthat I set out in this section. When I first startedPIC MCU programming,the dfuectives that I will introduceto you in this experiment werenot availablein the Microchip assembler products.For example,to declarea 16-bitvariable,you would usethe equ directive: il.o

equ

0x20

i

iHi

equ

0x21

t

Decla!€ a 15 bit starting at aaltlress 0x20

variable

to declarea 16-bitvariableastwo eight-bitvariables. The declaration format sholvn in this snippet is known aslittk mdianbecausethe leastsignificantbytesis declaredat the lower-fileregister.This is the format usedin many 16-bitprocessors(e.9.,the Intel 8086), and I feel that it makesintuitive sense.Theproblem with this format comeswhenyou are usinga debugger to displayvariables;inthe debuggera numberlike

cbLock ir2 enilc

i

w $r.t.

0x20 -

"i"

iE

a 15 bit'

(2 Byte)

valiabl€

and the low addressbyte (in little endianformat) is accessed asthe variable,and the high addressbyte as + 1.To showhow thev are accessed. here variable the is an initializationstatement: movlrr' 0x123{ - ((0x123d / 0x0100) * 0x0100) novrdf i r i = 0x1234 novl$ 0x1234 / 0x0100 novwf i + 1

The first instructionof thesefour linesfinds the low eightbits of the constantvalueby doing an integer divideby eightbits (0x0100)and then multiplyingit againby eightbits.After the multiplication,the values lower than eightbits will all be reset.Subtractingthis value from the original will retum the value of the lower eightbits.The upper eightbits are simplycalculatedby eightbits,or shiftedto the right by eightbits. Thesetwo calculationscould be built into defines.but Microchiphasprovidedthe HIGH and LOW directives,which perforrn the samecalculations.The four previousstatementsthen become: InovLw novwf

w

IJow 0x1234

r i = 0x1234

i

S e c t i o nN i n e A s s e m b l y L a n g u a g e R e s o u r c e R o u t i n e s

20L

ba; s-,1

fs rlJ

l-rj

$5 r:nl 6*t

{ }

tn 1_t,

movlw mov\rf

{l}

G} ',..{

-a d

.rl

i{ {$ qt (, Fl

r-l

{u

4J '*{ i{

a I

\s r-*

HIGM'.1234 i + 1

Understandinghow to declareand access16-bitvalues and variables is a good fraction of the work requiredto use16-bitvaluesin your assemblylanguageapplication.The remaining part is to understand how arithmetic operations pasqcarry,and borrow information from the low byte to the high byte of a variable.In this experiment'sprogram(asm16Bit.asm), I demonstratehow declarations,initializations, increments,decrements,addition, subtraction,and conditionaljumps are implemented. "es'l15Bit title 09€rations"

-

r\ t \

'-{ {, . F.{

Itaralwale NoteB ! PIC15E58{ rulrtriag at { UHz ilr Reset ia li€il tlirectly to Vcc Pul Lup/ Programl.ag Heralwale

STATUS, C

i a c f

i + 1 , w

adawf

j+1,w

movwf

D€slinalion

movf

j,

auborf n o v f btfEs

D€gtinatioD, j + f . w

iDeEtination=i+j

Incrom€at Eigh Bt t€ if, R€EuIt of t Lo$ B!.ts€ Atltl ie > 0x0Fl' (Carry Set) wlltten for low ; Not€: a|lal uial-Rang€ r PIC UCUg so no rradlallet i

1tr

+ 1

w

r Deslinalion Deatsination

STAEUS, C

,

j

rd

i

sultrf

Destinalion

+ 1,

sulrwf novf btf6a l n c f autwf btfss golo

j, w i+1,rt sTATItg, c i + 1 , n j+1,!t STATUS, C Errolloop

Sinuleto! vl'a

+ 1.

IJISE R=DEC INCII'DE'rp15f

ElrolLooD:

j:2, Destiaatlon:2 ENDC

Declaration t vari.abl€ (2 Byle) r 16 Bil Couater

PAGE 0 i R€quir€dl TCD2

fo:. l.tPI|IB

"i" with r rnitialize 123{5 al€cinal t High Byte Fl.fat

movlw riovwf lrovlw lrovwf

IIIGE 1234 i + 1 L@l L23{ i

llovlw movwf movlw nowf

IIIGII 56789 j + 1 rJow 56?89 j

,

lncfsz d e c f

i, f i + 1 , f

i i

i n c f

i + 1 , f

t

blfsc

STATUS, Z

alecf flecf

202

i+1,f t.

f

(i

,

if

i

i is ifump

> j)

hitialize

"J.

ui" lDcr€ment Incremen! High Byte if Reault of Increnenl ing lJolr Byle

rifl fiecreneat D€c!€neat Eigh ByEe if IJow Btte is equal to r initsielly i i

goto

E!!or

Less than j, Tak6rr, Error

if

Everytshing

Codrpare ODeration diftn't lrork cofiectly

i

684. incn gtolo

ors noD

(Lo!t If Cerry R€set By!€ Negative) Tak€ ole ltore Alray from th€ High Byte f

t Finish€d, okay

CBIToCK0x20

= - j

f

!A[ke Prealko 0{.09.21

lj.1

'*

blfac

lacf

l.{

s

i, w J, w D€stination i+1,w

15 Bit

D€alonalrate 15 Bit Varieble Declaration, Initializatioo, additio[, Eublraction, incr€rr€nting alecren€nt ing anat cod[)erisod operations.

! f*

Ddlotrstlat€

movf atLlwf rnofitrf movf

ErrorlooD

€Dd

Note that the conditionaljump hasa bit-skip instruction that follows the samerules as the eight-bit conditionaljump codepresentedin Section8.This meansthat the tablesusedto definewhich valuewill be subtracted(andfrom where),and the tablesusedto define the flag state for the bit-skip instruction are exactlythe same.The conditionaljumpcodefor a valuebeingequalor not equalto zero is a specialcase that canbe testedby simply ORing eachof the two bytesof a 16-bitvariabletogetherand checkingthe zero flap:. inovf

Lab€I,

ct + 1,

,

iolrrf

Lab€I

blf,ac gotso

STATUS, Z gL:rteenBilzero

w

i

i

OR Low Btrte rrith Eigh Bytse (bolb Z SaE if, reEult lrytea ) ia zero iturll) value

ia sixteen ia zero

bit

This exampleillustrates that although the different operationspresentedin asml6Bit are usefuland can usuallybe usedwithout modification,somecasesexist wherebetter codecanbe producedwithout the same number of instructions.For exarnple,think about how to implementaddingan eight-bitvalueto a 16-bit

l , e 3 P I C @l l C U E x p e r i m e n t s f o n t h e E v i l

6enius

variableand what would be changedfrom the previous codeto do so, When you have worked through the different operationslistedin asm16Bit,you shouldhavea good idea how to performbitwiseoperations. You shouldalso recognizethat the bitwiseoperationsare somewhat simplerthan additionand subtractionoperations

becauseyou do not haveto carry or bonow. Multiplication and division are somewhatdifferent than bitwiseoperationsor additionand subtraction,but you shouldbe ableto comeup with someideason how they canbe implemented.(Section12will examinedifferent methodsof multiplicationand divisionthat can be usedasa basisof these16-bitoperations.)

78-Universal DelagMacro Experiment

fsl {lt L'

6$ rlt

:'il

t''i' movlr movlrf alocfaz g o t o

When I discussed delaysin C programming,I probably seemedpretty nonchalantaboutit; basicdelayscould be implementedusingfor loops,and more precise delaysusingbuilt-in timersand critical signalswould be output from customhardwarebuilt into the PIC MCU. For C programmingand relativelyfeature-rich deviceslike the PIC16F684,this is a pretty good attitude to take.But whenyou are working with simpler PIC microcontrollers, which do not havemultiple timersor CCP rnodules,you are goingto haveto programa delayyoursell Programmingdelaysin PIC MCU canbe donesurprisinglyefficientlyasthe macro in this experimentdemonstrates. The PIC's clockis dividedinto four parts,eachof whichprovidesa differentfunctionin the instruction rycle.By knowing the clockspeed,you can easily period asthe reciprocalof derivethe instruction-cycle the PIC MCU's clockspeeddividedby four. Every instruction,exceptthe onesthat changethe program counterexecutein one instructioncycle,and this knowledgecan be usedto createsimpledelays.As you might expectthe nop instructioncanbe usedto delay one instructioncycleand the following instruction: goto

$+1

r Delay tswo iaBtruction cycles

will delaytwo instructioncyclesusingonly one instruction. If you needto delaymore instructioncycles,you canusea smallloon like this one:

i i t

Loatl

Countser

Declenent Loop Back

oremmino

,i

''

the count€r to count€r

Eachloop executesin three cycles,and a maximum of 769instructioncyclescanbe delayedusingthis method.Note that I am usingthe relativeaddressfor looping:Multiple delayloopscan quickly run out of your list of stocklabelslike BitDelayloop, and you'll end up with labelslike BitDelayloopT.Theseare not recommendedbecausethe loopsare probablycopied and pastedfrom other partsof the program,andyou may not alwaysrememberto updateall the label references.A jump to an incorrectlabel can be very difficult to seein a program.By avoidingtheir usein delay loops,you will eliminatea possiblesourcefor pro-

i,i" aa:a

*

:.n

crrnrc

For longerdelayqyou will probablyseethe needfor a 16-bitcounterand might want to usea loop like this one: rnovlw morwrf movlw novwf alecfsz goEo al€cfsz goto

HIGH Count Dlay + 1 LOW Courlt Dlay D1ay, f t-1 Dlay + 1, f S-3

r lJoaal 15 Bil

Counte!

* :l-.'i

Decrement

r Decr€menu t I,ooI) Back By!e

IJow Byte Bigh Byte to Low

{:i3

This codeworkswell, but it is extremelydifficult to comeup with a 16-bitvaluethat will delaya specified numberof cycles.I usethis codeto give me a quickand-dirtyapproximate200ms delayby resettingthe 16-bitDlay variablebeforeenteringthe loop:It's fast, easyto code,and doesn'trequireany thinking on my part. The following codeis the recornmendedway to use a 16-bitdelaycounter: novko monwf movlw

5ection Nine

Cyclea Dlay f Dlay, $ - 1

EIGE

(count

DIay row (Count

+ 255)

r

Loafl

15 Bits

+ 256)

A s s e m b l y L a n g u a g eR es o u r c e R o u t i n e s

203

!.;}i,

i!!

{r ;t

a;

aatal].w

-1

t

Decldment Byt.e

btfsc a€cfsz

sTATus, z Dlay, f

,

Decremen! High ByUe IJooD Back

goto S-3

.H t t rlt

br

This codehasa constantloop delayof five instruction cyclesand requires one fewer instruction and file registerthan the more obvioussolution.The 256is addedto the cycle count to ensurethe correct number of loops(otherwise,if the high byte of cyclesis zero, the codewill loop 255extra times,and whenit is not zero,it will loop one time lessthan you want it to). I shouldpoint out that the lastpassthough the loop executesin four cycles,and with the three overhead cyclesbefore the loop, the cycle delay can be written out asthe followingsimpleformula: Cycl.eaDe1ay

&,1

{tl

&q G} L'

! ,

P-

=

(Counl

* 5)

+ 2

In the program asmDlay,I have taken advantageof this delay and the one- and two-instruction-cycle delaysshown previously to create a macro that providesa precisedelayto a specifiedcyclecount.In the program, I have listed the macro and put in a number of teststo make surethat it executesfor the specified number of cycles.The nops after eachmacro invocation are usedto set breakpoints before and after in order to time the code'sexecutionusingMPLAB IDE'S Stopwatchto test the operationof the macro. tit.I€

.d

i

lJolt

"aamDlay

-

Creatse

a ltnivelsa1

The nDlay'r rnaclo Ln lhis loutine t dlelays ranglng fron 1 to 1.000,000 cycl€a. r Haralware Notes: r PIC15A584 runrring at { MHz in t ReE€t ia tied alirectly lo Vcc i Pullup/PlogrEll[ling llalibrare i r ,

Delay

r3i1l

Droviale

Slmulato! via

l4yke Prealko 04.09.22

r 1

$,,.

,"{ IJ

\t

P.{

X

sd

_coNFIG _FCI{EN_OFF & IESO_OFF & _BOD_OFF & _CPD_OFF & _CP_OFF & _!,ICLRE_ON & _PWR!!E_ON & & _rNTosclo _vrm_oFF CBIrOCK 0x20

t Varialcle Declalation 24 Bit r Requilea (w/ WREG) Count.e!

D1a]rya1u€:2 ENDC Dlay Dlacro CycL€s variable C'yclesl,eft varlaltle largeNum = CycleE CycleslJefl locaL IJongloop

204

i

r Can't Hanall€ > 93 SeconflE (e { !'lllz)

> 0*0{FFFF00

Cycles

"R€quireal error Delay is longer than rDlay, !{acro caa suDDort,l 6ndif if Cyclea > 327581 lJoop? t Ne€dl Large IJargelnrm = cycfe6l€ft / 327 6A! novlw IJarg€Iilum + 2 novwf DLat4lalue Number of t Calculate t oopa LouglooD I t R€DeaE for Each IJoop D1at4ra1u6 + 1 clrf t Do Ma:rimrm Poasible IJoo9 Coun! clrf Dlayvalue dlecf Dlayvalue, f blfsc z s!!a!!us, tlecfsz Dlayvalue + 1, f goto 9-3 dlecfaz Dla]^lalua + 2, f , ReD€at IJooD goto Longloop - ( (IJarge!tum * 327581) + qlcleal,ef,t = Cycleal€ft 1+(LargeNul[*3)) ontlif r Neeal Irarg€ lJoolt if eyclea > 1{ a IJooD be r WilI required? - 3) / 5) + 256) rovllr IIIGH ( ( (Cycle6lefE novwf + 1 Dlat^Ialue - 3)/ 5) + 256) novhr l,ow ( ( (Cyclesl,eft nonrdf Dlay'Va1ue tlecf Dlayvalue, f t 5 C]'cle Conslanl D€Iay tooD btfac STATUS, z + 1, f, alecfsz Dlat4ta1ue goto $-3 - (3 + (5 * ((Cyclesl€ft = Cl'cleaI,eft CycLeglef!

- 3)/ s))) e|talif vhiLe

C'yclesl.efl

goto Cyclealef,l if

; >= 2 t

$+1 = Cyclealeft

Cycl€slefl

== 1

Fini8hed lrith I,ooD Cotle Pltt- in 2 hatruction cyclo D€Iay6 - 2

i

Put ia tslr€ IJast Requileal Cycle

nop €ntlif €ndn

LIST R=DEC INCIjTDE rD16f 68{. inc"

{t

lf

PAGE olg no9

0 r Requireil

Dlatz nop

3

r shoulal

DIay nop

4{

r Dolay

for be goto

4{

t

DIay no9

r Delay

0.1s

Dlay 5000000 noD

t Delay

5a

Dlay

t Delay

50s

50000000

K€eD Tlack of Rdlalnlng C?clea

1 na De1ay

; Finish€it. Okay

Eve4.thiDg

ead

l , e 3 P I C @l ' l C UE x o e r i m e n t s f o n t h e E v i l

& nop

CycL€a

Dlay 1000 noD 100000

!@LAB ICD2

Genius

I would considerthis macro to be a combinationof If you wereto read showboatingand overachieving. throughthe application,you would seethat it is limited to 83 million cycles(83 secondsin a PIC MCU running at 4 MHz), andit providesaccuratedelaysto the instruction cycle.This accuracyis usually required for long delays,but for short delays,the accuracythis macroprovidesis not required.You might want to cut the macro down for your own use and avoid the initial loop, which is required for delayslon ger than 327,681. cycles(a third of a secondwhenrunning at 4 MHz).

If you comparethis applicationto othersin the book that are designedto run only in the MPLAB IDE simulator,you might think that my inclusionof the _CONFIG directiveis an oversight.Generallyit's not requiredin the simulator.However,in this casethe _CONFIG directiveis required.In the testingof the simulated delaysthat are longerthan 2.9seconds, PIC MCU would resetitself due to the Watchdog Timer resettingthe processor.Toavoidthis problem,I addedthe standard-CONFIG statementto make surethe WatchdosTimer is disabled.

133 :r!::

:,i,, tr:

il: . ,.n

ExFeriment79-High-Level Programmingin Fssembler andwould producethe following statements: ,l

tbsf novf tbef IbEf rnovwf tbcf

STATUS, RP01 i, w STATUS. RP0l STATUS, RPOI j sTATus, RP0l

: . f.-.1 !_-

for the macro invocation: ASSIGN J,

When I first startedworking after university,I waspart of a team developinga high-performance functional testerfor electroniccircuits.One of the taskswe had wasto comeup with a programminglanguagefor the tester,and I havealwaysbeenintriguedby the solution that waschosen.Ratherthan comeup with a custom compilerfor the programminglanguage,a standard compilerwasselectedandits macroprocessorwould be usedto convertprogrammingstatementsinto the data requiredby the tester.Tosomeextent,this effort wassuccessful asit did producedata,unfortunatelythe compiler'smacroprocessorcould not prodtce enough of it. Much of the data wasin the form of tables,and the maximumtable sizethe supportedby the macro processorwas32 KB. So far in this section,Ihavegiven you a macrofor conditionalexecution(or if) statementsand a macrofor precisiondelays.And, I wanted to seeif I couldcomeup with a macrothat would support assignment statements, becausewith sucha macro,I felt I couldclaim that I had developeda highlevel languagethat ran under the MPLAB IDE assembler. Unfortunately,I couldn'tdo it in ore macro.It requiredtwo.Thefirst macro,ASSIG\ wasusedto assignthe contentsof a variableor a constant(literal) valueinto a variable.Its format was: ASSIGN DeB!,

Equalsign,

alTtt)e,

SectionNine

Soulc€

or

:iiiu

novlw tbsf novwf Ibcf

47 STATUS. RP01 i sTATus, RPol

for the macroinvocation: ASSIGN

i.

=,

n.t.

47

The settingand resettingof the RPObit of STATUS is dependanton the positionof the variables.I could haveoptimizedthe macroto eliminateone set of bcf/bsfstatementsif both variableswerein bank 1,but I felt this wasgood enough.The blank ( ) or period (.) dTypeparameterbeforethe sourcemacroparameter indicateswhetherthe sourceis a variableor a literal. Thereis no way the macroprocessorcan determine which is which. I originallywantedthe ASSIGN macroto be ableto handlenot only straightassignment statementsto vari ables,but alsotwo-parameteroperations(like add or subtract).Unfortunately,I wasn'tableto discovera methodto determinewhetheror not a parameter waspresentand,in any case,if any parameterswere missingthe macroprocessorwould flag an error.So,I addedthe secondmacro:

A ss e m bI y L a n g u ag e R e s o u rc e R o u t i n e s

205

.:.tLr.

l -.i

OPERjATE Dest, EquaLSigm, alTtrpe2, Soulc€2

alTl.pe1,

Sourcel.

Ope!,

and would produce statements like: movl$ lbsf Bubwf tbcf tbsf movwf tbcf

47 STATus, RPol j, w sTATus, RPol sTATus. RPol i STATUS, RPol

for the macro invocation: OPERATE i.

"

-,

",

j,

-.

n.n,

47

The OPERATE macroputs in the secondparameter wasfirst to load WREG with the subtractorif the subtractionoperationis selected. To test the ASSIGN and OPERATE macros,I created asmAssign.asm: "aslBssign ti!1e Assignment llacro "

-

Experiment

with

an

This Drogran tl€monslralea hosr an assigfirent Inacro f,or the PIC MCU coulal be createal. Earahrare Notes: PIC16E68{ running

at

4 r!trIz in

Sinulator

Myke Predlko 04.09 .24 LIST R=DEC INCLUDE ip16f584.

cBr,ocK 0x20

inc" r variable

Declaration

ENDC ASSIGN macro D€st, Equalsign. variabl€ _aai = 7, _aa) aaj Equalsign _aai (_aai != _aai ) if rrNo Equala ('=,) elror in else r (dr!|I)e != ".") it , ( Source > 0x7F) if bsf, STATUS, RPo , endif movf Source & 0x7!'. nr ( source > 0x7F) if bcf, STAAUS, RPo r endif r movlw Sourc€ endif (Dest > 0x7F) if bsf stATus, RPo t enalif mowqrf D€st & 0x7E (Des! > 0x7E) if bcf STATUS, RPo t endlif endif

206

flTl.pe,

Souree

Assignnent Slalement Equals Present variabl"e Direc! Aank

1 Variable

Bank

1 Variable

Liceral

Bank

1 VariabLe

Banh l

variable

OPERATE nacro Dest, Equalsigm, alBrpel, Sourcel, Oper, ilTtpe2, Source2 = 7, variable aaj ,aai _aaj Equalsisn -aai (_aai != ,aai ) if "No Equal8 ('=,) elror in A6signment Statement t Equala P!€sent " . " ) (dr5/pe2 != if Dilect r variable (Source2 > 0x7E) if bsf STATUS, RPo r Bank 1 ValiabLe enali f nowf Souree2 & 0x7F, w (source2 > 0x7F) if bcf STATUS. RPo r Bank 1 Valiabl"e endif elae r Lit€ra] movlw Soulce2 enalif (alTtrpel != n.r) if Dilect t variabLe ( sourcel > 0x7F) if bsf STATUS, RPo t Bank 1 variable €nalif ((1 oper 1) == 2) if Operato! r Aaldlilion addwf, Sourcel & 0x7F, !r' eLse ((47 oper 25\ == 22') ; sublraction if Operator subwf, Sourcel 1' & oxtF, etse ((3 Oper 2) == 3) if t OR Operator ionrf Sourcel & 0x7F, w elae ' AND op€rator ((3 Oper 2) == 2l if anahrf soulce1 & 0x7E, w ((3 ope! 2) -= !) ' xoR operator xorwf Sou!c61 & 0x7F. w else "Unknolen Operatorrr 6!!0r enalif €ntlif endtif entli f endif if, (Sourcel > 0x7F) bcf STAIIUS, RPo t Bank 1 variabl€ endif el"se t Litelal ((1 oper 1) == 2) if Op€rator r Aalalition aaldlnr Sourcel else ((47 ope! 25) == 22) r subtraction if Operator subLw sourcel eLse ((3 ope! 2) == 3) if r oR operator iorlw soulce1 el6e ' .aND operator ((3 ope! 2l == 2\ if anallw Source]. else ((3 oI)€! 2, == r, i xoR OPerator if xorlw sourcel if

rrunknown Operatsor" error endif endif endif endif endif, endif, if, (Dest > 0x7F) baf STATUS, RPo t Bank endif

l , e l P I C @l l C l - JE x o e n i n e n t s f o r

1 variabl€

the Evil Genius

novwf Dest & ox?F (Deal > ox?F) bcf STATUS, RPo endif, endlif eadm

Prc15F584

t

ruDning

in

Prckit

1 stalter

kit

tql X

if,

t Ba.Dk 1 Varia.ble

i t

!'lyke

i

04.o9.28

Pledlko

b

r Reguireal rcD2 =' =, =,

ASSIGN i, ASSIGN 1, ASSIGI{ J,

for

UPIll|l

" "' j t.d, 47 tr n, TRISC

o P E R A T EI , = , " " , ) , + , O P E R A T Ei , = , " " , ) , & , O P E a A T Ei ' = , " " , ) ' - , OPERATE OPTIOII_REC, =, n

$

t

ry

FCIIEN OFF & -rESO_OFF e _BOD_OFF & collFrc CPD OEF & CP OFF & MCLRE-ON & _P!|RTE_ON & _lsDn_oFF & TNTOSCTO

cBrocK ox2o

Declaralion

i variable

".", 47 ".", 47 ".n' 47 tI OPIION_REC,

Fiuishetl,

Everything

d (*

2{ Bit r Dlay Requirea (w/ WREG) Counter

Dlayvalue:2

}J. ;-a 5

fD

t, J ENIrc

&,

..n,

AggIGll nacro Deat, Equalslga, ASSIGN necro sroulce ttot rr

OPEIIAIIErracro Dest, goto

t9

I.IST R=DEC INCI,UDE "p16f584.inc"

PAGE

Okay

ODer, tlTtzge2, oPERAIEE t;

ilFtzpe, ahown

Equalsign,

Source

{

ttTyDel,

gourcel,

\S

Source2 not

gholoa

ea(t DLay llacfo

When you test this application in the simulator, you are going to discover it is extremely difficult to follow the progress ofthe code;execution will bounce between the macro invocations and the lines inside the code.You might want to look at the Disassembly Listing, but common statements are listed one after the

other in the macro definitiong making the code even more difficult to follow. Your best resourcefor seeins how the macrosproducethe necessary codeis in the sourcecodelisting,asmAssign.lst, which providesthe insertedmacrosand indicatorsfor activestatements. Unfortunately,the MPLAB IDE simulatordoesnot stepthroughthe listingfile. From my perspective, this inability to simulate effectively the application is the biggest drawback to

Cl.cL€a

Dlav tnacro Eource not Ehoffn

;t

onceper secondand is written injust the ASSIGN, OPEI{ATE, Dlay, and ifgoto macros (the body of^ which I have deleted from the folloritititJ,iiJl,

l-,,

PAGE ors

€ Fd

o

nor)

t R€quir€tt ICD2

assreN poRTl, =, PoRrA' =. 1::I9I ff:]:il ff:;y'=;' AssreNrRrsa, =,

for

n.s, 0 i hirialize ""' oxrr

!!Pr.At

variableg

r R€lurn trele when Done

rJoop:

"o*ro,toT]1Y,",1'?."ii""u

ifsoto i, ==, j, setDo Assrc!{ PoRrA' =' ""' 0 o""o "3i13,

assrcN poR![A, soto

rJooD

t Turn off the LED

<< {)

r Ttrrn oN th€ rJED ' R€peat

eE. titLe

'a6ro[E].asb

-

FLash

DO usinc

rlaclosn t

Hiah

trevel

dlenonstratee how the Eish rever :*-::::^::"n'"lilacros ca! be use.r to FraEh the Prckiys Do i rrED. I

aardware Notes,

5 e c t i o nN i n e

h

ry

8-1

fn l'"t 0,

After a lew moments of study.you should be able to understand what is happening in the application code. However, if the appticiilon code dio not execute as expected when it is programmed into a PIC MCU.I would think it would be a major effort to find the problem in the program logic or the macro code.

Assembly Language Resounce Routines

!-{

4 &

,,. ;;' ,t n.n, b,001111,

ASSIGN J,

writingcodewitfthesemacros.A;;ondaryconcernis 3}|{o|:tl:t=,,,,,

the possible difficulty in reading what the source code is doing from the macro invocations.To illustrate what I mean,I created asmMFlash.asm,which flashes D0

H

ifgoro !{acro varr., conp, va!2, DeEt ir ifgolo nracro soulce nots Ehovn

2O7

F{

H F 1". |1 .X sd

Pq

ExFeriment 80-lmplementingFlead-Onlg Hrrags

Ft H

New Program

Counter Address (Goto/Call)

Fr

PC lncrement Pfogram l\4emory Read Address

F {

8-Elgment Program Counter Stack

It

L,'

d

'tl l-al

hr

la.{ I-

t I I

w +; \u . r.{

l-({

Read-only arrays are useful and effective solutions to a number of different programming problems.Typical applicationsrangefrom storingASCIIZ strings employedasusermessages in a format that is reasonably spaceefficient, to providing a translation table for different applications,and using a jump table to different locationsin an application.In a von Neumann processorarchitecture,a read-onlyarrayis normally implemented in program memory as a seriesof bytes that can be accessed by indirect addressing.The Harvard architectureof the PIC MCU doesnot lend itself to this simple solution, and more complex software is requiredto return read-onlyarraydata. To accesstabledatain the PIC MCU, you will have to perform what is known as a computedgoto whercin the processorwill calculatethe addresswherethe data is locatedandwrite this addressinto the program counter.If you rememberthat the PIC16F684has 2,048instructions(11 bits wide) and the databuswidth is eightbits,you may be wonderinghow this is accomplished. In the PIC16F684(and all the other mid-rangePIC microcontrollers), two registerscan be written to that allow programaccessto the processor's program counter.Thefirst registeris calledPCL and is actually the lower eight bits of the program counter (seeFigure 9-3).The upperthree bits in the PIC16F684(and up to five bits in PIC MCUs with a full 8k of programmemory) of the programcounterare loadedfrom the fivebit PCLATH register,the contents of which are wdtten into the programcounterany time PCL is updated.Thismeansthat for computedgotos,the addressspaceis effectivelybroken up into 256-instruction addressblocks.UnfortunatelyMicrochiphasnot givethis block of instructionaddresses a label,so you will seeawkwardtermslike "256-instructionaddress block."To implementa computedgoto,you mustfirst load PCLATH with the appropriate 256-instruction addressblock valueand then write the lower eisht bits of the addressto PCL.

208

Full program counter

Figure 9-3

Although it seemsthat I've wanderedoff topic a bit, I want to note that performing the computed gotos is half the problem of implementing a read-only array. The secondhalf of the problem is to load the appropriate array value.Fortunately,the designersof the PIC microcontroller have provided you with the retlw instruction,which providesa sirnplemethodof retuming a read-onlyarrayelementin WREG To take advantageof the retlw instruction,a subroutinewith a computedgoto is called.Ifyou look at differentPIC MCU applications,you may seea read-only array implementedin the samemannerasthe following subroutine, which returns the ASCII character for the nybblein WREG: Hera'lable: aaLlwf retlw relLw ll!etllr letllr relllr relllr relllr !6t1!t rethr relllr relllr retllr retllr relllr lethr !e!hr

r conv€ft cha! PC!, r0, t1, \2t .3' \4' '5' '6'

rwbbLe

ia

I{REG to

H€x

f

'8' '9' rA' rB' 'C' 'D' 'E' \F,

There are two issueswith this function.The first is the useof 16 retlw instructions. To easethe workload of creating read-only arrayg Microchip added the dt directiveto the languageto passits parametersto an appropriate number of retlw instructions The dt directive'sparameterscanbe ASCII stringsset in double

l , e 3 P I C @l l C U E x p e r i m e n t s f o r

the EviI

6enius

quoteqASCII characterssetin singlequoteqor numericvalues.Different data typescanbe concatenated,or linked,togetherusingcommas.The nybbleto ASCII conversionsubroutinecould be rewritten as follows:

INCLITDE "D16f58{.

inc"

?s1 6!d

variablea CBLOCK 0x20 St'!insr 18 t

r9 tfi

EIIDC

. i HexTable:

ailtlwf d!

r Converts char

Nybble

in

WREG to

PC!, f " 0 1 2 3 4 5 6 7 8 " ,0 x 0 3 9 , ' A , ,

ltej{

\B',

rnovlw

For rnorecomplexapplications, theseconditionscan be very difficult to meet,especiallyif multiple readonly arraysare built into the application.For these cases, a more generalread-onlyarraysubroutineis required.In this experiment'sapplication, asmTable.asm, I haveput in what I feel is the best read-onlyarraysubroutine.This subroutinesavesthe indexvaluein PCLATH, loadsPCLATH with the 256inshuctionaddressblock of the start of the table,and swapsthis value(in WREG) with the indexvaluein PCLATH. I must point out that PCLATH is only five bits,so the maximumnumberof tableentdesthat can usethis codeis 32.If you want more,you will haveto usecodelike that presentedin the following scheme. The indexvalueis then addedto the lower eightbits of the addressof the tablestart (and PCLATH is incremented if this value is greater than 0x0FF) and finally loadedinto PCL. - A R€atl Only

t i i

lhiF apDlicatLon copl.€s f:.dr a r€ail olrly tabl€ a variablo a!!ay.

t i , i i

Haltbrale Not€s: PIC15!58{ runainq at { MHz ia R€se! is li€d ilir€ct'ly lo Vcc PulluD/Progranmins Harfkfare

r , t

wilh

tsbe ASCIIZ stsling a|tal puts lt into

ltyke Pr€alko 0{.09. 17 or"t

Atray

*=o""

gimulalor via

ti..C

rc,,

The other problemwith the read-onlyarrayis that it will work only if threeconditionsare met: (1) the table datamustfollow the "addw{ PCL, f" instruction (whichaddsthe contentsof WREG to PCL and stores the resultbackin PCL); (2) the tablemust be totally within the first 256-instructionaddressblock (within the addressrangeof 0x0000to 0x00FF);and (3) the PCLATH register (which is loaded when PCL has the contentsof WREG addedto it) must be zero and not changedanywhereelsein the program.For many simple applicationswritten by beginners,theseconditions are not unreasonable.

"asnTalcle Eltle ItteBEage tr

'.r "

aop

a

movwf clrf IJooD:

String

t-r1

Point !o lhe Deatination Alray

]-t

EgR i LooD I'or charac!€r Gets Next Eldnetrt

novf

i.

w

caLL novwf

ReadlTabl€ INDF

incf

FsR,

iorlw btfss goto

0 STAlr['S, Loop

goto

$

Each to t{ull Allay

**

sto!€ Chafactse! ia valiabLe A!!ay Point !o l{ext R€aa Arlay Elem€nl Poiat !o llexts valiabLe Alray El€ment == 0? chalacter

f

t

Z t*:!r: Finisheit,

lool)

l..r ,11

subroutines i Readlable: movwf PCLATH novllr high ReatlTable xor\df

PCLATE,

f

xorwf

PCIATE,

w

xolwf

PCIATE,

f

aaLlhr

1ow _ReaalTalcle

blfsc incf,

STAgttS, C PCI,AEH, f

novwf

PCI.

S_$rap Conlenls of, PCI.ATH & WREG PCLATH = PCLATH ^ WREG waEG = WBEG ^ (PCI,TTH ^ WREG) WREG = PCIATH PCI|ATfl = PCLATE ^ (PCIJATII ^ WREG) PCIATH = WREG calculale Table offs6t > 256? Yes, Pot nt lo N€rrt 255 Atldr€sa BLock ituJqr to TabLe Elenent Readt only Table Sentsence Subj ects Cryptic verb

_ReattEabl€: tll alts alts dtr tll d r retLw retlw r€t1ra retLw retlw retlw

nMyk€ tr ra' + rE, 29*4 tw' - 4 L 6 , 2 0x77 0x5F 0x72 0x5D oxt 3 0

-

:i..:t:

Save Offset PCLATH Calculate

rA,

i

!".*

f.a i*r " ifl 'l.;.j sl !.!:

l'i

F } i,"*i

Noun

h'g

rR t Zero At St!iug

Endl of

&-d

n;

enal

SectionNine

:

A s s e m 1b y L a n g u a g e R e s ou r c e R o u t i n e s

es 209

When you read through and test asmTable,you will seethat it loads a file register array with the contents of the read-onlyarray.And, if you displaythe file registers,you will seea messagethat hasbeen(simplistically) encryptedin the read-onlyanay. As an exercise, I would suggestthat you try to come up with your own subroutine code that implements the generalread-onlyarray (i.e.,it canbe any'lvhere in the PIC16F684's memory;it is greaterthan 32 bytes,and its contentscanstraddlea 256-instruction address block). When you try to come up with your own routine,rememberthat you havea numberof directiveq suchasthe if directivethat can be usedasI havein the followins routine:

E!I6rdtabl6: clrf ((

if bBf

i PCIJATII i EenTable & 0x0100) PCLATH, 0

Relurn llex ASCII for Lslvbbl€ in WIIEG != 0)

Char

enalif (( Iler(lable & 0x0200) ! = 0 ) if baf PCLAAH, 1 endtf ( (_Ir$c!able if & 0x0400) != 0) bsf PCITATH, 2 endif antllw 0x00F ; rtust want low€r { Bits adatln l,ow _H€xTabIe lhe Correct t Calculate

off6et btfsc STATUS, C iacf PCITATE. f noverf PCI. _Ile*Tablel '0 L23{ 5578 gABCDEF"

Experiment 8l-Bata Stacks cationsandprinter control,and network-enabled printersallow datato be sentdirectlywithout the need of the printer switchand data spooler.But the data storagemethodsusedin this applicationare important to know as they will be required from time to time in your applications.

# /l

frt

u"t d

l\l

3 I

c-d

,&r *'{

,it

One of the first applications I designedfor microcontrollerswasa Multi-PC printer switchand data spooler.Thisdevicewould monitor the printer ports of multiple PCs,and when one startedsendingprint commandsto a printer,the devicewould passthem along to the printer.And if therewere other PCssending datato the printer later,their datawould be held in a memorybuffer until the first PC had finishedsending data to the printer.When the first PC had finished(I waited15secondswithout a new charactercomingin), the circuitwould then assignone and then passthe data of the other PC'sdata to the printer.Along with savingdatafrom other PCs,the spoolingfunction allowedthe PCsto passdatato the device,which "appeared"to be a printer,at full speed.Real directconnectprintershold the PC from sendingmore data until it hasfinishedthe operationit hasbeengiven. Thesefunctions allowed all the PCs connectedto the printer to work at full speedand have a minimal programdelaywhensendingdata to the printer.Today, modernmultitaskingoperatingsystemssuchasWindowsand Linux provide separateprocesses for appli-

2L0

Thereare two basicmethodsof storingdata temporarily. The first is known as the s/ack and can be modeledlike the stackof papersin an executive'sinbasket.When datais storedon the stack,other pieces can be stored on top of it (seeFigure 9-4) with the interestingresultthat the first pieceof data on the stack will alwaysbe the last piece removed from the stack.For this reason,stacksare knowr aslnstin frrst oLl (LIFO) memory To demonstratethe operationof the stack,I created asmStack.asm, in which I haveset up a 16-bytedata arrayin bank 1 for the storageof data.Tostoreand retrievedata on the stack,I createdthe Pushsubroutine:

/-------\ /

"Stack"

Fieure9-q

l , a 3 P I C o I ' l C UE x o e r i m e n t s f o r

Stack

the Evil

Genius

Outgoing

ht |

trstackn affay // Put Deta i! | / Al E1€dl€n! nstackPtrn

Pueh(Data)

(StackPtr == SlackEop) leturn ctv€rFlowE:afoli Pointer at €ndl of // The stack els6 // if

stack 5ti11

SDace Left

t = Datai SlacklstackPlrl = StackPtr + 1, SlackPtr retuln //

]

Save Data Poidt to Nexts E1€n6at

// //

PuEhcoodl,

€nil

Puah

And the Pop subroutine, which operates as follows: int

Po9()

//

Relurrl Data the gtack

a!

lhe

Top of

{ - 1) = stackBolton) ( (stackPtr r€tum ltnal€rrlowErroli Nothtng ltr gtack ela€ // "PoD' alatsa off Stack t stackPtr = stackPlr - 1r // ltov€ to r,ast gtack Eleneat

if //

r€luln

StackIStackPtrl

,rop

#*:

3;i.

novlr

20

novrdf, cllf

i i

PuahlJoop: novf call caLl incf tl€cfsz

goto

//

I feelthatlimit checking is important.evenifit is ignoredby thecallingcode;itensures thatno memory

j, !t T€Jr1€Read Push j, f i, f

outside the allocated stack array area is accessed. To simplify the limit testing in asmstack.asm,I took advantageof the bit a;ngement of a t6-iit uutter

golo

$

,

Finiahetl,

i

Push Value

t subroutineg Puah. bsf, STATUS, C

leturn

"olo.rr,

4

il}l"", rs", r

"

oroo

dl6cf

FgR, r

whenyou simulateasmstack.asm.

novf bcf

INDF, w STATUS, C

Eabl€Reeil movwf movlw novwf novf aalfllrd btfac lncf nofirf Table:

I -T€dE) HIGH ,Tabl€ PCIATE w _T€rrp, r,ow _Table STATITS, C PCIATII, f PCL

i t r

program rhis slack coulil Irqrl€oenteal

t r

llarahcare Not€a: PIC16F684 ruELng

i , ,

lryk€ Pr€tlko 04.L2.29

tl€monsllat€s be La the Prc

at

Si

holt

ple

Mcu.

{ MEz in

simulator

t Variable

_Tellp E![DC

olg

0

S e c t i o nN i n e

p

(-f

on glack

El€rlen!

Loop

onlo

have t A].leafly Elem€nta? t 16 El€m€nta, Error

,

Pop ToD of

Forever

Stack

16

Declaratiorr

OO

I

u

g, rF p,

Retuln

Q

Stack

i Notshhs nlt€r€?

rt g,

i Y€s,

ta

Return

Erlor

i Erse, Return toD Brrle

r Randlom Tab].e

r PORTA nnd IBISA Tabl€ valu€B

Bit

dt 47, 23, 33, 2, L90, 4t, 37, Ar, 42, 2r, 94, 74, 79 dr a, 6a, 54, 29, 37, 9!, t-0O

t IgT R=DEC INCIJTTDEn915f 58{. inctr CBLOCK 0x20

Va1ue

slack

F.

3 o

value

gtacki

a 15-Eleme!t

o

P

It also means that data can be lost, as you will observe

Denonstlate

gee what,s

r PoI) rop

a one,then I know I havegoneoutsidethe stackarray and can stop trying to accessinvalid memory locations.

-

t Gloto Next

Pop i, f, PoDLoop

srArus' c :::,, ollii"rr"t"tu"' "

"agnslack

llanalon

i

rsR, w

ti!1€

Get

r\ghTJooD

xonrf

with bit 4 ofthe addressalways being zero.If it is ever

i

Data onto gtack

20 i

Llj*, li"i-

X

Ft r Itah

FSR,

tql

t

leEuln

6nal PoD

!4PLAB ICD2

, stalt stack al 0x20 in Bank1

] )

f,or

novlw novflf PoDLoo9 ! call tlecf,az goto

blfBc

t

r Requi.r€al

6ad

When you run asmStack.asm and executethe Poploop, you will seethat the data is retrieved in oppositeorder in which it wasinput.This makesa stacka poor choicefor spoolingdata in the application mentioned at the start of this experiment.However, it

Assembly Language Resource Routines

2LL

}f U'

makesa stackan excellentchoicefor savingdatathat may be temporarilyoverwrittenand in needof retrievaloncethe operationthat overwrotethe data hasfinishedexecuting.Stacksare usedin the PIC MCU for savingthe programcounterwhen calling

The originalprograrncounteris saved subroutines. beforejumping to the subroutine.It is then retrieved when the subroutinehascompletedand the original programcountervalueis required

Experiment 82-Eircular Buffers Although I've drawnthe circularbuffer asa linked list,it can be easilyimplementedasa simplearray.For examDle. the Put functioncanbe modeledas: i,n

Put (Data)

int

Put Data Circular

//

Into th€ Buffer

t j.f ( ( (PutElement GetElenent) relurn

In this experiment,I will introduceyou to the circular buffer,which retrievesdatain the sameorder asit was written and is ideallysuitedfor the printer switchand buffer applicationI mentionedin the previousexperiment.

:-

.1

t , '

The circularbuffer consistsof a circular,singly linked list of data elements(seeFigure9-5).The buffer hastwo pointers,one pointingto the next location wheredata will be storedand one pointingto the next locationto be readfrom. If both the next storepointer andnext readpointer are pointingto the sameelement,the buffer is empty.Conversely, if the next store pointer is pointingto the elementjust pdor to the next read element,the buffer is full. Justa few instructions are reouiredto imDlementthesebasicrules.

==

+ 1) % Buffersize)

PutNexl + 1== (FuLL ) ReadNext the Dala El€menl / / Can Slore

Buffer!\rl1t

//

€lE6

t Buffe! [ PutElernent I = Datat = (I'utEl€menl + 1) PutElen€n! retuln Putcooali // fi I // End Put

)

e. Buffelsize,

And the Get functionis: int

Cet()

//

( int

the Next Buffef

Get uhe

value

in

T€dr!)t (GetELernent

if

r€tuln eLse

--= PutEl€nents)

Buf felEnutty, //

Elemenl

NoEhing

//

to

to

Retrieve

t T€trll) = Buffer

,1',,ti

Next Element )

j,t,.r.

Get lhe Eleneat = (GetE!.€ulent + 1) % Buffersizet GetElement relurn Tetngi // Retuln the ELenent // fi I // Enal cet lcetElement

],

//

To demonstratethe circularbuffer function.I createdasmCBuffer.asm, which usesthe same16-byte (0xA0 to data areathat wasusedby asmstack.asm OxAF).Thisallowedme to usethe sametrick to make surethat data outsidethe allocatedmemoryis not allocated(if bit 4 is set,the pointer is outsideof the circularbuffer).

i,.i

NextElement to Writeto

tit.le Buffert

"aEmCBuffer

t t ,

This proglam Circular Buffer coulal

i

Earahfar€

circuLa!

how a 16-ELement be Implement€dl

Figure 9-5

Circular buffer

212

t r e l P I C @l l ( U E x o e r i m e n t s f o n t h e E v i l

in

the

NoleE:

6enius

PIC MCU.

PIC15F684

running

at

4 UEz in

Simulato!

t novf

u!'k€ Pr€tlko 0r.12.29 TJIST R=DEC I N C T T T D En D 1 5 f 5 8 4 . i n c n CBIJOCK 0x20 _!!dE) _CBuf,f,€lPul, ENI'C

i

variable

Declaratiof

_CBuff€rG€!

0 Requireal tcD2

for

Stalt Buf,f,er in Bank 1

MPr.aB

al

0:{2 0

_CBufferPut _CBuff€rcet nrovlv lrofitrf clrf I\tIJooD 3 rnovf caLl cal,I incf tlecfaz golo movlw movnf GetlooD: caLl

r

nonwf xorwf baf blfac

FSR CBuffelPut, STAT['S, C STAT['S, z

movf incf bcf bcf,

INDF, w _CBuff,ercel, _CBuf,feleel, STATIIS, C

rc i

i|t

C.

thea

w

t4 X tn

t Nothing t Get the

h{

to Get Valu€

*.J.

f, 4

EF{

:U F"t

PAGE org no9

cBuffercet,

GeE Nex! value Buffer rF Put == Get, Notshtngl

20

dr 47, 23, 33, 2, 94, 74, 79 atr a, 64, 54, 29,

J

i

Put' Dala

i

G€E Rantldr

i

Goto

20 t

i

gee !l?rat,s

cet

i

Gel Next E].ement

j, w TableRead Put j, t i, f IttIJoo9

al€cfaz goto

i, f Getl.oop

goto

s

Next

t Finiaheal,

Into

auffer

value vaLue

on stack

Buffer

IJoop Eorever

subroutia€s Pul Value inlo cilcu1ar Buffe! movlrf movf movwf

_T€tq) CBuffelPut, FgR

aaltllrd andlvr

1 b'11101111,

r.olwf bsf, btfac

CBuffercet, STArsS, C STAtgS, Z

novf novlrf Lncf bcf bcf

w _Teq), IIIDE _cBuff€rht, _CBufferPlrl, STATI'S, C

TabIeReaal: novvrf _TerE) movhr AIGH ,Table movwf PCI|ATE movf Te!E), rd ailillw I,ow _Tab1e blfac STATgg, C incf PCIATE, f movwf PCIr _T6b1e:

w t Can,l bave Put i rf Itnreadl Dala Buffer t IIBEG haa VaIue

8ina1

== Gel in

eet

rt

i

No llore Space Slole Value

f t fncr€Erenl Pointe! 4 t Keep within Range i No Erlor

SectionNine

r Rarlalom Table

s*

Rr , PORTA andt TRISA Bit TabL€ valu€s 190. {{, 31, 43. 42, 2L, 37,

9L,

t I

1-OO

C J 5-i.

6ntl

you When you havesirnulatedasmStack.asm, shouldhavenoticedthat datais retrievedin exactlythe sameorder it wasplacedin the stack.You shouldalso havenoticedthat the maximumstorageof data in the circular buffer is one byte lessthan its total size.This canbe a concernto new programmerswho expectthe data structuresto storeeverythingavailableto the device,but in practicalterms,it really isn't a problem. The important considerationwhen using a circular buffer is that the averagerate of data removalmust be greaterthan the averagerate of datainsertion.For the printer switchand spoolercircuit,I found I had to increasethe sizeof the buffer to 256kilobytesof DRAM beforeI couldreasonablyexpectto avoid a conditionwherethe incomingdatawould fill the entire circular buffer. At 256 KB, the printer switch buffer could storeabout 100pagesof text,which wasusually more than threepeopleworking on PCscould generate beforethe printer finishedprinting.In most cases, it is not practicalto keepincreasingthe sizeof a circular buffer to meet the expandingneedsof an application; you will probablyhaveto put in somekind of"handshaking" to tell the sendingdevicethe circular buffer is full and enabledata sendingonly whenspaceis availablefor more data.

A s s e m b l y L a n g u ag e R e s o u rc e R o u t i n e s

2t3

[,4

t--t H IAJ

h& Hr fft Fx€

rn

Experiment83-Heading and [Jriting the EEPHOMOata Memorg

F\

rrovf

*-l

Addleaa,

lh€ AfLlleag r c€l to b6 Reaal

vr

STA!!I'S, RPO EEA.DR ^ 0x80 bsf novf

tlt

bcf

rr{ IU

et

FEr t4{ Fll

lei

L*{ $ tqJ

!

!

ar) ffi

Earlier in the book,I introducedyou to the PIC MCU's built-in EEPROM datamemory or in other words a number of bytes built from electrically erasableprogrammableread-onlymemoryandcan be usedfor data storagebetweenpower on or resetcycles of the PIC MCU Accessingthe EEPROM in assembler is a bit trickier than in C whereHT-Softhasprovided you with macrosthat will read andwrite the EEPROM for you.In this experiment,I will present you with the informationand codeyou needto access the EEPROM aswell asdemonstrateits operation usingthe sameapplication,but I'11do so in assembler, asI usedearlier. The EEPROM control hardwareis accessed by four registerslocatedin bank 1 of the PIC16F684. In other PIC MCUs, you will find these registerslocated in multiple banks,which makes the coding of the accesses more difficult.Two of the registersare usedfor passing a databyte at a specificEEPROM addressand are given the labels EEDAT and EEADR, respectively. Thereare two control registers:EECON1 (described in Table9-1)and EECON2,which is a key sequence register usedto ensurethat data is written correctly. Thesefour registersare usedto read and wdte the EEPROM datamemory. To perform an EEPROM rcad,the following instructionsequenceis used: Table9-1 EEC0NIFesister Bils

UJ F € r

Bits

Label

Unused(Return 0 when Read)

7:4 3

Function

WRERR

d!!

Setwhen write operationdid not complete coffectly write enablebit, set beforestart ofwrite operation

(f,"

2t4

WR

Wdte start bit,set to initiate wdte operation

RD

Read start bit

r g€l lhe aaltlr€Fa to Reatl

EECON1 ^ 0:.80, RD EEDAT ^ 0x80, !r

r Loatl in Byte dadalleaa n

at

STAEUS, RPo

Performing an EEPROM write is abit more involved asit requires the two-byte write to EECON2 to allow the wdte to take place.In the sequencebelow, notice that I store the addressin a temporary register at an addressthat is shadowedbetweenthe two banks before changingexecution to bank 1. novf

AaLlleaa,

!t

novwf

0x70

movf bsf noverf novwf

.tg Data, STATug, RFo EEDAT ^ 0t 80 0x070, w

novwf baf movf,

i

Get the Aaldresg lo be R€afl in t Store ahailowetl regisler

0x070 ia aame in Bank regiEter o/L EEA.DR ^ 0x80 t get the aaldreBg to lllile EECON1 ^ 0x80, WREN r gtsarl writso oDeratl.on EEDAT ^ 0x80, w r lJoaal Ln Btrte al "Adlttr€aa. r

bcf, DOp movlw

STA|!US, RPo

movwf movlw mofidf bsf

EECON2 ^ 0x80 0rrAA EECON2 ^ 0x80 EECON1 ^ 0x80,

WR

btfac

EECON1 ^ 0x90,

WR

golo bcf

S-1 STATUS, RPo

0x55

t

gtart of Requileat Sequ€nce

Enal of R€quiled S€qu€nc€ fo! wflte t wait to Cdll)L€ts€ i

This write sequenceis different from what you would seein a datasheet.I wrote it asa generalcase, and it will not return until the write hascompleted. In most applications (like the code usedfor this experiment),I will not poll the WR bit for completion at the end of the write;insteadI will checkit before startinganotherEEPROM access, asshownin asmEEPROM.asm:

l , e l P I C @l l C l JE x p e r i m e n t s f o r

the Evil

Genius

t'asmEEPRoM - Display/Save a value using till"e the EEPRoMtr ; a saveal EEPRoM This program DispLays , on vaLue Unlese lhe Button t RA3 is presseal antl th€n the AI)c is Displayeal. r is ; When t'ha Button ReLeas€dl, the A.DC Value is Saveil in EEPROM. ; This coale is baseit on ; ' t i ; ' r , ,

rlalahrare Notes: PrC16F584 runningr

in

PIckit

1 starter

kit

Myke Pretlko O4.72.2a IJIST R=DEC INCLUDE np16f,684. inc"

t

incf cal-L xotlw btfsc goto InitEEPRoM: clrf movlw catl incf movlvt call incf mowlvt call incf movlw call iIICf movll' call

== otAA?

t EEPRoM(3)

Gootl t Yes' Pattern the EEPRoM t hitialize

!'SR 0 EEPROMWTite FsR, f oxEF EEPRO!4Write FsR. f 0x55 EEPRoIqwrile ESR, f 0r.AA EEPRO!4Wfite FSR' f 0 EEPROMWTiIe

with

t Start

Nothing

Registers

FCr{EN-oEF & rESO OFF & -BoD oFF & -coNFrG & l{cr'RE oFF & -PWRTE oN -cPD oaF & cP-oF!' -wDT oFF & rNtoscro Variables cBLocK 0r{2 0 r, j Display, OldDisplay Buttonstat€ ADcstate. Dlay, TemP ENDC

HArIEEEPROM: 4 novlw mowf ea11 mowwf

;

;

FSR, f EEPROMRead oxaa z sTAlus. IIaveEEPROll

lJoop: movlw movwf novf novwf Displayloop: novf -

PAGE I'tainline org clrf novlw novwf novLr'

O PORTA 7 CMCONO b'00000001'

mov f bsf movlw nltrovwf

ADCONO STATUS. RPO 1 ANsEr, a Ox80

novl$r

b,00010000'

novwf bcf clrf clrf

ADCON1 ^ OxgO STATus. RPO ADcstate Bultonstat€

clrf call xorlw btfss EoIo incf call xollw btfss groto incf call xorlw btfss Eolo

FSR EEPRolrReaaI 0 STATUS, z IniIEEPROM FSR. f EEFRO!4ReaaI oxFF STATus, z hitEEPRoM FSR, f, EEPROMReaaI 0x55 sTAlus, z rnitEEPROliI

i

Turn

of,f

comParators

r rurn on the ADC with: ,Iuslif,ieal : Left ; vdll inB€ead of, vr€f 0 ; channel t Do Bank

1 Inits

ilust RAO as Analos InPut the clock as r select Fosc/8 i

r Init

state

variables

t

; EEPRO!I(2)

-=

0x55?

value

FsR EEPROMReaaI DisPlaY Loop t Displav i ],oop through the 8 t'EDs

7 i Dia!)lay. TemP

Each

of

w

t Get

1:-*

PORTA value

the

calt rlf btfss novll' novwf novlw adalwf, ca1l. bsf movwf bcf novl"w mov$tf, movll' adalt$ btfsc decfsz qoto clrf Inovlw

PORrATabl€Reaal Ternp, f t STATus, c 0 t PORTA 8 t i' w PoRTATableRead STATUS, RPo TRISA ^ 0x80 STATUS, RPo IIIGII ((2000 I 5l DlaY Low ((2000 / 5\ -1 t STATUS, z D1aY. f $ - 3 PoRTA t ! t

Eubvtf btfsc goto

f i' STATUS, C DisplavLoop

sanalle btf6s grolo

Press Button PORTA, 3 ButtonPreaa

or

ctrf btfss goto clrf movlw mo\twf

ADcstate Butlonstate' l,oop Buttonstale 4 !'sR

Releasetl t Button 0 t Ilave Nevt A.Dc value? t No' ,Just Return

t E E P R O T ' I ( 0 )= = 0 ?

r EEPROU(1) == O*FF?

Diaplav Initial EEPRo!'I( 4 )

,

up Temp to

Shif,t Bit

Reset'

Get

TRIS

Test

No write Pattern

+ 256) + 2551 Displav

LED f,or 2 ms

Turn Off r,ED Take 1 AwaY from DisPlaY

, l'oop

Until

i

the

== O*FF

Ignore t RA3 P?esseal?

i Wlite

New value

S e c t i o nN i n e A s s e m b l y L a n g u a g e R e s o u r c e R o u t i n e s

2L5

nlovf cal]. novf novwf goto

Display, w EEPROUWTiIe r' OtaLDiBpfay, Diap1ay loop

movf

ADCStsate,

btfBa goto baf Lncf

SAATUS, z BPADgtalel ADCONo, GO ADCState, f

r Roslore

Display

rnovlw tnovwf bsf bcf letuln

Value

oniAA EECON2 ^ 0x80 EECON1 ^ 0x80, STATITS, RPo

WR

EEPROUREA'I :

goto BPADStAt6l: xollw btfaa golo btfss iEcf

\r

i Wbat La the state?

.eDC Operation r Start to lhe Ne*t ; Increnenl Stale

IJooP t R€aal the

ADCState,

fol r wai! FiniEh

noverf

movr.!'

3iiilll;"I",

o

' saveDiaplavvalue?

7. Butlonslate ADmSH,

mov!'r

Diaplav

clrf

iu)Cstate

soto

rJoop

rd

0 .-{

t! 0) 1d .*{

st6t€

Machine

'r

Values

Contenta ;;;-";-;;;;,-;" Wrile

of,

FSR

EEcolt1 ^ 0x80, wR i waits for EEDAT ^ 0:.80

novr

FsR, w

l*

novwf bsf nop novlw

EEADR ^ 0x80 EECON1 ^ 0x80,

novwf

2L6

i

Stote

EECON2^ 0x80

Woral tso Write

.

37 instructions that the PIC16F684's (and all midrange PIC MCU's) processor recognizes. The instructions are listed in Table 9-3.I recommend that vou trv

The MPASM assemblerdirectivesare listedin Table9-4.Many of the directivesare listedfor completenessand will not be requiredduringnormal programming;thesecasesare markedin the table.Also note that the list directivehasa numberof arsuments: theseare listedin Thble9-5. "Use of this dfuectiveis In Table9-4,the message not recommendeddue to unknownooeration"indicates the directive is carrying out its function by insert-

ing instructions.The instructions usedare unlnown, may affect the contents of other registerq and may

$REN

r stalr

0x55

previous

w'i!e ro cdE)lere

solo s - 1 novwf

:

to memorizetheseinstructions, a brief explanation of what they do,andthe registersthey affect).Youwill be ableto programmore efficientlyand be ableto think aboutwhat instructionand the algorithmto be usedto solvea programmingproblem.

RPO

L) ts{

t PoRTAan'l TRrsA Bit

b , 0 0 0 1 00 , ilt b , 1 0 0 0 0 0 , , b , 0 0 0 1 0 0 , , b , 0 0 0 1 0 0" b'000010' alt b,001111,, b,001111,, b,101011,, b'101011' dt b,011011,, b,011011" b,111001., b'111001'

btfsc

.

the originalvalueis displayedand the lastADC read valueis storedin EEPROM, to be displayedthe next time the PIC MCU is resetor poweredup.

Table 9-2 lists the different parameter options for the

b,010000,,o,tooooo,,JTJtooooi,

w

displayed on the LEDS. when the button is released, '

For Eonsideration

C

EEPROI'twlit€:

The asmEEPROM,asm code is a direct translation

of cEEpRoM.candperformsidenticallyto it (the

f,or

PCIATH ErcH _PoRTAtabLe PCIATH, f PCIATH, !t PCIATE, f

STATOS,

r,f

Dotentiometeron RAO is readbv an ADC and then

ADC vaLue

Table

bEf

AaldreaE Reaal Byt€ at AaLlroaB

, Get

r Ciet Table vaLueE Irigbt Display

inc! pcr.Ar*, t novrdf pcl. I -PoREATable

.rt

EEDAT ^ 0x80, gTATuS, RPo

glore

starter kit,s button (on RA3) is pressed.when the PICkit 1 starter kit's button is pressed,the value of the

a'lfllw r'ow PoREArabre l-t

movf bcf !€EUrn

Previous cor$)let€

t !{ark Diaplay value gav€al

r ReEet

r subroutLn€a PORTATabIeR€aal:

ST.nmS,

S - 1 ASR, rd EEA.DR ^ 0x80 i EECON1 ^ 0t<80, RD i

fo! to

valuesavedin EEPROM is shownunlessthe PICkit 1

OIdIDiaplay

nrovf

blf,ac

goEo rnovf movltrf b8f

WR t wait write

aDC R6aal co

i sav€ the sar\9Le varu€

mov!,f,

noficf novlw xolwf xorsf xolwf

STATUS, RPo EECON1 ^ 0x80,

f,

BPADState2:

ffi:"

baf btfac

ADC Va1u6?

1 gtATItS.

Z BPA.DSlale2 ADcoNo, co

r R€adl EEPROU at Adalresd in FSR

ADc

of Required

sequence

change with different versions of MPLAB

IDE,&4PASMassembler.

l , e 3 P I C @l ' l C UE x p e n i m e n t s f o r

the Evil

Genius

trl

Table9-2 sgmbolsUsedin the PIC Dataand EesllnatlBn Listedin Tableg-3 MEUFEEembler lnstructions Sgmbol

FunEtion

D

Destination instruction: can be either f for register or w for WREG

F

Register address:seven bits for direct addressing within a bank

k

Bit specification for iNtructions, only 0 to 7 valid

kk

Eight-bit constant value: literal inshuction argument

kkk

Eleven-bit constant value: goto and call instructiotr addrcss

p

PORT register: for PIC16F684,only 5 (PORTA) and 7 (PoRTC) are valid.

Z

STATUS, Z: zero bit

c

STATUS, C: carry bit

DC

ST:ATUS,DC: digit carry bit

o

r'1

o o p

u

,-,.

g

o

rt

0,

(+ l-r'

o 5

Table 9-3 PlCl6F6Etl(and Mid-HangePIC)MicroEontroller Instructlon5et lnstructlon Flass Flffected Instruction Dperatlon addlw kk

Z,C,DC

Add constantkk to contentsof WREG and storeresult in WREG.

addwff,d

Z,C,DC

Add contentsof registerfto contentsofWREG and storesum either ilr registerfor in WREG

andlw kk

Z

AND constant kk with contents ofWREG and store result inWREG

andwf i, d

Z

bcf f, k

None

AND contents of register f with contents ofWREG and store sum either in rcgister f or in WREG. Clear bit k in register f. Inshuction operation is: f = f & (0x0FF " (1 < < k)).

bsff,k

None

Setbitk in registert Instructionoperationisf= f l(1<< k).

btfsc I k

None

Skip following instruction if bit k in register f is reset (0).

btfss f, k

None

Skip following instruction if bit k in register f is set (1).

cal kkk

None

Saveaddressof next instruction and load PC with new addresskkk.

clrfl

Z = 1

Clear (load with 0s) register I

Clrw

Z=7

ClearWREG

clrwdt

None

Clear the PIC MCU'S watchdog Tfter (wDT).

comf f, d

Z

Tll.ebits in register f are inverted and the result can be stored either in register f or WREG

decf I d

Z

Decrement the cotrtents of register f by one and store the result in either register f or WREG

decfszf, d

None

Decrement the contents of register f by one and store the result in either register f or WREG. If the result is equal to zero, then skip the next instruction.

goto kkk

None

Load PC with new addrcsskkk.

incf t d

Z

lnc'ement the contents of register f by one and store the result in either register f or WREG.

incfsz f, d

None

I[qement the contents of register f by one and store the result in either register f or WREG If the result is equal to zero, then skip the trext instruction.

iorlw kk

Z

lnclusive OR constant kk with contents of WREG and store rcsult in WREG

iorwf f, d

Z

lnclusive OR contents of register f with contents of WREG and store sum either in register f or in WREG

movl f, d

Z

Passthe contents of register f thiough the PIC MCU processor'sAlgorithm,ilogic U t's (ALU) zero check and save them either back into register f or in WREG

movlw kk

None

Load WREG with constantkk.

mowvf f

None

Store the contents ofWREG in register I

nop

None

No-operation for one instruction cycle.

S e c t i o nN i n e

Assembly Language Resource Routines

2L7

Table 9-3 (continued.) PlCl5F58q[and Mid-FlangePlEl MicrocontrollerInstructionset lnstruction Flass Bffected lnstruction Operalion option

None

Storethe contentsofWREG in OPTION_REG.Notq useof this instructionis not recommendeddue to devicecompatibilityissues.

retfie

N/A

Restoreprocessorintelrupt requesthardwareto waiting stateand retum to instructioninterrupled.

retlw kk

None

Load WREG with kk beforeloadingPC with addresssavedby callinstruction.

return

None

Load PC with addresssavedby call instruction.

rlff,d

C

Rotate registerf to the left with bit 0 beingloadedwith the curent carry flag.Bit 7 of registerf is storedin the carry flag.Theresult is storedin either in registerf or in WREG

rrff,d

C

Rotate registerf to the right with bit 7 beingloadedwith the current carryflag.Bit 0 of registerfis stored in the ca y flag.Theresult is storedeither in rcgisterf or in WREG

sleep

N/A

Put the PIC MCU into a low-power mode.

sublwkk

Z,C,DC

Subtractthe contentsofWREG from constantkk and storethe differenceback into WREG

subwff, d

Z,C,DC

Subtractthe contentsof WREG ftom the contentsof registerf and storethe differenceback into registerf orWREC.

swapff, d

None

Swapthe leastsignificantnibble with the most significantnibble of registerlThe swappedvaluecanbe storedback in either registerf or irt WREG

t sp

None

Storethe contentsin WREG in the specifiedPORT register.Note Use of this instructionis not recommendeddue to devicecompatibilityissues.

xorlw kk

Z

ExclusiveOR constantkk with contentsofWREG and storeresultin WREG

xorwf f, d

Z

ExclusiveOR contentsof registerf with contentsofWREG and storesumeither in registerf or in WREG.

Table 9-4 MPF5M Fssembler Directives Functlon

DlEctlve

o

,t{

"tJ tu

f{ 0l d .r{

._badram exprl-exprll,exprf-expr]l

Specify registers that should not be accessed.Whena direct accessto these registers is made, MPASM assemblerflagsthe instauctionwith a warning.This directiveis normally usedonly in the Microchip written part number .inc file to define the PIC MCU part trumber register ranges.

-badrom exprl-exptfl, exprf-exprll

Specify program memory addressthat should not be accessed.When instructions are found in these regiongMPASM assemblerproducesa warningor erlor. This directiveis normally usedonly ilr the Microchip w tten part number .incfile to definethe PIC MCU part number addressranges.

-config expr

SpecifyPIC MCU configurationword value.Option specificationequatesare found in the Microchip written PIC MCU part number .inc file.

-config expr

Speciry16 bits ofdata to be storedin non-program-accessible memory.Generallyusedfor serial numbersor programrevisioninformation.

_maxtara expr

Directive usedto specifymaximumfile registeraddress. Like _badram, this directiveis normally usedonly in the Midochip writtet pa number .inc file to definethe PIC MCU part numberregiste{ ranges.

maxrom expl

Directive used to specily maximum program memory addres$ Like -badrom, this directive is normally usedonly in the Microchip written part number .inc file to definethe PIC MCU part number regtsterranges.

{0 L{

U t"r trt

#definelabel Istringf #1ncl,Jdeinclude,file

Declarea text substitutionstring.Definesdo NOT replacecompletelineslike macro$

#undefile ldrel

Delete label previouslydefined.Previous(above)instancesare not affected.

#v(expr)

InsertASCII valuefor expr in the st ng du ng macroprocessing. Used to differentiatelabelsalgorithmically.

bankisel ldbel

This directive will set the IRP bit of the STATUS register according to the value of label. Use of this ditectiveis not recommendeddue to unknownoperation.

banksel laDel

This directive will set RPURm bits of the STAIUS register according to the value of label. Use of this ditectiveis not recommendeddue to unknown oDetation.

2L8

Load the contents of the specified file into the assemblylanguagesource file.

l , a 3 P I C @l ' l C UE x p e r i n e n t s f o n t h e E v i l

6enius

Table 9-4 kontinued) q t

cblock lexpr]

Start variable,structure,and equatesat specifiedvalue.Labelsbetweencblock and endcare given mcrementingvalues.Larger value numbersare specifiedby a colon (:) after the label.

Uabel]codeIROM_addressl

Not requiredfor singlesourcefile applicaUsed when objectfile is createdfor linked applications. tions.

const^ntlabel=er.ptf. . . ,label:exprl Specifya constantvaluefor a label.Seealsoequ. Createda packed14-bitASCII string(i.e.,sevenbits per character)in programmernory.The Uabeflda expr L exp2. . . . , expml PIC16F684cannotaccessthis daia.

i t

llabe\ dat^ expr,l,expr,. . . ,exprl vabell db erprf,expr,.. . ,exprl

Storedata asfull instructionsin programmemoryThe PIC16F684caDnotaccessthis data.

fn

ReseNeprogrammemory with packedeight-bitdata.ThePIC16F684cannotaccessthis data.

li"J,

flabel]de expr [, expr, . . . , expr]

Define data to be burnedin data EEPROM during PIC MCU programming.

llabell dt expr [, expr, . . . , exprl

Define table bytes(retlw expr).

flabel]dw expr[,e4r, . . . ,expr]

Rese e programmemorywords.The PIC16F684cannotaccessthis data.

else

Usedwith if directiveto indicateend ofprimary optionsand stat of secondary.

end

Indicatethat the end of the sourcefile hasbeenreached.

endc

End cblock label assignments.

' ! !

endif

May follow else. Used to end if conditionalassembly.

'-*,

endm

End macrodefinition.

endw

End while loop.

label equ expr

Assignthe valueof expr to the label.Seeset.

error String

Forcean efior with a message string.

fl\

gu

errorfevel{0l1l2l+t1s8ruml-msgnumlInhibit printing or displayingspecificerror and warningmessagenumbers. Exit ftom macrowithout processingany followingmacrostatements. exitm expand

Expandall macroinvocationsin the listingfile. Used with list and noexpand.

externLabel [, Label . . . ]

Declarethat the specifiedlabel is locatedin a linked file.

Uabe\ flll instuctlexpr,count globallabel[,label . . .l

Fill programmemory startingat the current address, with the specifiedinsftuctionor value.

Uabe\ idata IRAM addrcssl

Declarethe start of initializationcodein a linked application.

lfexpr

Begin block of conditionallyassembledcode.Completedwith either else. . . endif orjust with endii The if codeand other conditionalassemblycodecan be nested.

ifdef label

Begin block of conditionallyassembledcodeif label is present.Theifndef is a complementary directive.Completedwith either else. . . endiforjust with endif.Can be nestedwith other conditional assemblycode.

lfndef label

Begin block ofconditionally assembledcodeiflabel is ,ot present.The ifdefis a complementary directive.Completedwith either else. . . endif orjust with endil Can be nestedwith other conditional assemblycode.

list llist_option,. . . , list_optionf

If just the list directiveis on a line,listing is printed.Usesparameterslistedin Table9-5.

locallabel l,label. . .l

Define conditionalassemblylabelslocal to the current macro.

labelmacrofarg, . . . ,ergl

Declarea macrowith optionalparameters.

messg"messagetext"

Generate a messagein the listing file.

noexpand

Turn off macroexpansionin the listing file.

nolist

Tirrn off code listing.

flabellorgexpr page

Specifywhereaddresscode is to stafi.

p Eesellabel

Update PCLATH pagebits for the specifiedlabel.Use of this directiveis not recommendeddue to unknown operauon.

processorprocessor_rype

Specifyprocessort'?e. Use of this directiveis not recommendeddue to the processortype being specifiedbY MPLAB IDE.

ftdix default_radit

Insteadthe r: option ofthe Specifynumberradix type.Use of this directiveis not recommended. list directiveshouldbe used.

Define a label that can be accessed by other linked files.

Start a new pagein the listingfile.

5 e c t i o nN i n e A s s e m b l y L a n g u a g e R e s o u r c e R o u t i n e s

2L9

Table 9-4 (continued) MPFI5MFssembler Eirectiveg Dlrectlve

Function

flabell res mem_units

Reservespecified program memory for other linked files.

label selexpr

Assignnume c valueto label.Similarto equ directive,but label value can be changedwith additional set directives

spaceexpr subtitle "sur_te.rt"

Insett expr blank Iines into the listing file,

title"title_text"

Specify st ng for top line of each listing file page.

vabefludatafRAM-addressl

Declaresuninitializeddata areain Iinked objectfile.

llabeq udata acs\RAM-addressl

Declares uninitialized data area in linked object file for PIC18 series line PIC midocontroller$

Uabequdata ovt lRAM-addrcss]

Declares a section of overlayed uninitialized data in linked object file.

Uabell ldata sht fRAM-addressl VariableLabel[=expr][, . . . ]

Declares a section of shared uninitialized data in linked object file.

while expr

Loop code within while . . . endw until the expr is rot true (or zero).

Specify secondliDe of program title.

Declarevadablewith optionalinitial value for assembly.

Table9-5 OFtionalParametersFlvailableto the List Eirective

'

riniiii

b:#

Set tab spaces. Eight is the default.

c=#

Setcolumnwidth. Default is 132.

f=hexfileFormat Specif, hex file output format.Default is INHX8M and can be INHX32 or INHXSS. F.ee Allow ftee-fomat parser.Default is "fixed." mm =OFF

Turn off memorymap displayin listingfile.

n=#

Specilythe numberof linesper page.Default is 60.

p:type

Specifyprocessortype.Default is definedby MPLAB IDE processoroption.Use of tlis list parameteris not recommended.

pe=type

Specifyprocessortype and enableextended instructionset.Availableonl] in PIC18series PIC microcontrollers.

r=radix

Specifyoct or decnumber radix. Default is hex.

st=OFF

Tum off symboltable print in Iistingfile.

t=ON

Truncatelines.Default is OFF and will cause linesto wrap to the next one.

w=0 | 1 | 2

Setthe reportingmessagelevel.Seeerorlevel directive.

x=OFF

Turn macroexpansionofl Default is ON.

":-1 r \

rd i!'l

0l "Fl

r l f-i

n &x{ 220

l , a l P I C @f i C u E x p e n i m e n t s f o r

the EviI

Genius

Section

Ten

5ensors

1 DMM 1 Wire st!ippers 1 Ne€dle-nose

pliers

2 Bleadboards 1 Wiring

1Plcl6F684

1 4.7k fesistor

1PIC12F5?5

1 1k res istor 4 10k resi stols

2 tLC251. 1 Two-line dj.splay I

by 16-character

LCD

4 47of,) resistors 2 33oO !esistors

?4LSt?4

2 2200

1 Sharp GP2D120 IR ranging 2 38 KHz IR TV remote

module

control

1 U-shaped IR opt o- intelrupt (see text) 1 10-LAD bargraph 3 Higfh-intensitY

er

47 pE elect:.olytic

LEDS

L electret (1N4148) silicon

2

10k breadboard-mountable tiometers

I

10k 10-pin

capacitor

4 0.0L pF capacj,tols 1 16-button

1 ]R LED fN9f4

(R

4 0.1 /rF capacitors

4 LEDS (anY color)

f

poten-

resistols 2 10k light-dependant decleases with 1i9ht) 2

display white

resistols

2 10of,) !es istors 1 1k breadboald-mountable t iOmete!

1 2N3904 NPN tlansistor

diode potea-

SIP

I

keypad interface midlophone

SPST breadboald-mountable

switch

4 bleadboard-mountable on pushbuttons

momentaly

1 Four-celI

clip

2 Three-cell

Or I

kit

Ail battery AA battery

clips

10 AA batteries 10k resistols

1 5V lanteln

2 3.3M !esistols

battely

1 55nn black heat-shrink to 1.2sinches (2.5 to

2 2.3M lesistors

When I passedarounda proposedtable of contentsfor thisbook,this sectioncaughtmany eyes,asan introduction to sensorswasfelt to be useful for robot developers.Atfi$t,I wasa bit disappointedby this response

I tubing, 3 cm) long

becausethe topics I cover in this section are actually requked in many different microcontroller applications;it providesyou with many of the basicsneeded to changeenviroffnental parametersinto valuesthat

22'1

canbe processed by the PIC MCU This informationis usefulfor both microcontrollerapplicationandrobot developers. The topic of proper sensorinterfacingand dataprocessingwould take up a book at leastequalin sizeto this one,but in this section,I will introduceyou to someof the differentsensorsthat are typicallyused with microcontrollersaswell asprovideyou with a simple intedace that will allow you to create efficient multi-MCU applications. An important aspectof implementingsensorinterfacesis characterizingthe parameter being monitored andthe approp ate time intervalbetweensensing operations.Instead of rusingsensingoperations,I will usethe more commonlyusedterm pol/lng.The polling intervalcanvary widely and accordingto the characteristicsof what is beingpolled.In Table10-1,I have listedsomedifferent thingsthat are typicallysensedin microcontrollerapplicationsalongwith someideas about the appropriatepolling interval. The applicationspresentedin this book are actually very simplesensorapplications. Thereis very little processingdone on the data other than magnitudecomparison.And, in many commercial applications,the rate of changeand projectedfinal valuesare calcu-

lated.Beyondthesecalculations, when you are trying to identify an objector a total environment,the processingrequirements can be formidable. To simplily the experimentspresentedin this section aswell aseliminateany integrationissuesyou may haveusingthe sensorswith somekind of user interface,I am going to break from tradition and usea simpleinterfaceasa basefor complex,multiprocessor applications. When mostpeoplethink of a microcontroller interface,they think of an asynchronous serial interfaceusingthe non-retum-to-zero(NRZ) protocol of RS-232(the serialinterfaceusedin PC Modems). The problemwith this protocol is the needfor dedicatedhardwareto wait for and decodethe incoming signal.The PIC16F684and many lower-endPIC@ MCUs do not havethe built-in serialinterface(called a UART), so different communicationsmethods are necessary. The methodI choosefor this sectionis a sl'nchronousserialinterfacethat I originallycameup with for Ihe TAB ElectronicsBuikl Your Own Robot Kitmis interface takes advantageof the Parallax BASIC Smmp2 (or BSZ) built-in SHIFTIN and SHIFTOUT synchronousserialdata transfers. The PIC MCU

Table 10-1 EnvironmentalParameterEuJithFppropriateSensors and Folling Intervals Parameter

Sensor

Ambient Light Level

Light DependentResislor(LDtuCDS Cell) 200 to 500 ms

LDR responseis generally100ms.

SectorLight Level

LighrDependenr Resiqlor(LDR/CDScel

200 to 500 ms

Multiple LDRS or a singleLDR on moving turet usedto characterizeenvironment.

Object Location

DigitizedVideo

15 to 30 ms

Object identification;locationdetermination can changewith sensormovement.

Object Distance

UltrasonicRanging

100to 300ms

Sensormovementrequirescontinualpolling.

Object Collision

IR Reflection

50 to 100ms

Usually usedin safetyapplications(robot or operator);continuouspolling required.

Object Collision

"Whisker" or MechanicalSensors

20 to 100ms

Usuallyusedin safetyapplications(robot or operator),continuouspolling required.

SoundEvent

FilteredSoundInput

1to10ms

Short,loud eventscan be easilymissed.

SoundCharacteristic

FilteredSoundInput

50 to 200ms

Waitingfor tone or other easilyrecognized characteristicthat is presentfor up to several seconds.

Verbal Command

Digital SignalProcessor

500to 2,000ms

Speechprocessingrequiresa significant amount of time to complete,

vJ

Pollinglnteval

L-a

9 i

Eommenls

Ambient Temperature Thermistor-Calibrated TempemtureSensor 1 t o 1 0 s

The assumptionis that the ambienttemperature cannotchangequickly.

Fire,High-HeatSourcesDigitizedVideo,Pyromete$,LDRS

50 to 250ms

Typicallya safetysensorwith possiblerequrement for sourcelocation,generalrequirement to respondquickly.

Humansand Animals

Pyrometersor IR Reflection

250to 1,000ms

Typicalapplicationsincludeburglar alarms and automaticlights.

(Air) Pressure

Barometersor PressureSensors

5to60s

Pressurechangesgenerallytake placevery slowlyexceptin safetyapplications.

Humidity

Humidity Sensors

15to60s

Slow changesin environmentalhumidity.

222

l , a 3 P I C @l l C l JE x p e n i m e n t s f o r

the Evil

Genius

peripheralclocksdatain and out usingthe clocksignal producedby the BS2.ThePICSend(sendinga sevenbit commandto a PIC MCU from a BS2) and the PIC(sendinga seven-bitcommandto a PIC SendReceive MCU from a BS2and the PIC MCU respondingwith an eight-bitresponse)are demonstratedherein BS2 IF Base.bs2: r BS2 IF . Basic

BAS€ Bs2 to

r nPrcsendtr r suDgolteal

I ltrke

Template

PIC llCU InEerface

aaal ,'PrcsenttReceive' t OperationE

are

only

Prettko

. {$PBASTC 2.5}

- Put in B€lo\t

PICDatsa = 1

\ High

PIC MCU I/O

r Wait

fo!

progiam

PinE

PIC MCU to

Sta!€ments

. Sendl Basi.c MCU

as

Sets Up

Shown

cormanal

to

cosuB Prcsenal PAUSE 100 PICData

= 58L

. tvait Prc to Finish fo! PrevlouE . genal 0x81 anal Receive RegDollS€

GOSTB PlcsenflReceive DEBUG iPIC Respons€", ENI)

\ PICSenal are 1 - 8 Cdmanals r PlcsenalR€ceive Conlanils S81 - S88 r Prc Mcu rnterface Pins r Data Byte tso senal tolReceive PICData vAR Bybe ' IO Pina PC PIN O PD PIN 1 r setral the Byle in rrPrcDatatr Plcsenal: r Holal IJow foi 1 msec b€fore LOw PC ' shifting in DATA PAUSE 1 SEIFTOIJII PD, PC. I.SBEIRST, tPICDatsal HIGII PC RETIJRN

PD,

PC,

LSBPOS!!,

DEC(PICDat.a),

CR

PIC

$*. ;.J

a-,!

Eid

A PIC MCU applicationthat interfacesto this code caneitherwait for a commandfrom the BS2or continually poll and processthe sensor,polling the clockpin (PC in BS2IF Base.bsz)at Ieastonceper ms in order to not missthe beginningof any commands.If the samerequirementwasgivenfor an applicationthat interfacedto anotherdeviceusingthe NRZ protocol, the maximumdatarate would be approxirnately300 bps,due to the need to also poll the serial input line and still be ableto perform someusefulapplications. In contrast,the BS2takesabout2 millisecondsto send a byte,one-fifteenthof the time requiredfor the 300 bps NRZ sendtime. I realizethat few peoplehaveBS2savailablefor working throughthe projectsin this book, so in the first experiment,Iwill showhow you can simulatethe BS2usinga PIC MCU. With the additionof a simple LCD userinterface,you canexperimentwith different sensors.

S e c t i o nT e n S e n s o r s

IJ i r

IPICDAtA]

RET['RN

'variabl€s

' +*#* r

{n

Predko

SHIFTI}I

' {$srar{P Bs2}

Mainline IIIGII PC ITIGII PD PAUSE 1OO

I r4fke

codle Follows

r genal Ebe Byle in "PIcData" PICSenatReceive ! r HoLal lJolr for 1 maec befo!€ IJOW PC . shiftlng in Data PAUSE 1 SEIETOUT PD, PC, LSBFIRST, IPICData] r wait for Op€ration to PAUSE ]. r cdll)L€te

10o.,"".r.

\

r Prc Mcu rntserfac€

223

(u

?a

r 3

Experiment 8r-l-Plf MCUB5a User Interface

0)

U d

tt-.| h

1 Prc12F575 I

o

fwo-line by 16-character LCD dj. splay 7 4L577 4

P

g

1N914 (1N4148) si licoo dj,ode

H

l0k b!eadboard-mountable potentiometels

tl

1 10k lesistor

v,

1 B!eadboa!d-mountable momentary on pushbuttons

o

0 .01 pF capacitors DMM

p

Needle-nose pliers Breadboard

c{

Itiring

Three-cell clip

kit

a

AA battery

3 AA battelies

s U

X

U H

Pr

I

To createthe PIC MCU-based,simulated,BS2user interface,I usedthe two-wire LCD display first presentedin Section 6.The application shown in tHs section simulatesthe waveform clock lovoause lms/shiftout/clockhigh oI the PICSendBS2subroutine and the waveform of PlCSendReceive.In Figures 10-1and 10-2,I havecorrelatedthe differentfeatures of thesetwo waveformsto the BS2 statementsthat producedthem (listedearlierin this section).Thedata transfer is basedon a 14 g.sclock pulse over a 46 ps period for eachbit (seeFigure 10-3).The work to create the application code wasfairly substantial,and the need for precisetiming gaveme a good feeling for

writing assemblylanguagecode for the PICC LiterM compiler.The final result is quite easyto work with, althoughI discovereda potentialpitfall that you shouldbe awareof. The circuit usedfor the simulated BS2 interface (seeFigure10-4)usesall the availablepins of a PIC12F675.Inadditionto the two LCD interfacepins, the circuit assignstwo pins to a potentiometer/button userinterfaceandtwo pins to the simulatedBS2 clock/data lines.The circuit was built on a breadboard (seeFigure10-5)andis about ascomplexasI would like a PIC MCU breadboardapplicationto be. Included in Figure 10-5is the application circuit from

Flgure IDJ

BS2Send

Fisurel0-e

224

l , a 3 P f C c 'l l C u E x p e n i m e n t s f o r


q

(l 'd tl ,tl

P.t n IJ

gd

BS2Send.Receive

the EviI

6enius

P1 X

ro o

Ft

Fr.

o Figure f0-5 BS2simulntorcircuit on a breadboard and connectedto testsensoraDDlication Fisure f 0-3

@

BS2 Shifioutdan

|}5

the next experiment, to test out the operation of the interface and the PIC MCU code. The user interface consistsof a potentiometer that selectswhich command is to be sent to the PIC MCU instrument circuit. The user interface is capableof sendingthe comrnands0x01through 0x08 aswell as the responsecommands0x81to 0x88 by turning the potentiometer.To avoid the need of precisely setting the potentiometer, the first half tum selects0x01to 0x08and the secondhalf turn selects0x81to 0x88. Once the commandis selected,the button is pressedto

Clock t To S()nsor 1J C i r c uits I r-Data

P C 1 2 F76 tC v

10k

; F L

4

----l: 1 ir--

GPIOO 6PIO1 GPlO3

G PI O 5

l u F

GPIO4

sendthe data.If a responsecommandis sent,the responseis displayedon the lower line of the LCD. This method of specifyingand sendingthe command and then displaying the responseto the instrument PIC MCU is surprisingly easyand fast to work with. If you are looking for a simple-to-useinterface,you might want to consider using the method I provided here. The applicationcodecBS2Sim.cprovidesthe LCD, potentiometer, and button user interface aswell asthe two-wire BS2 comrnunicationssimulation code.The

74L5174 2

5Q/5D

3 6Q

Gnd

vc d

--J-

- r -

T .:

-

II I

15

I rox

4 . sv J_ .:

lI

I I I

0.01 |

u F l

L

( /

E

I J

10k

m o

|,/l

fi

1k

1Q/2D

H

r\}

dd

CLR | 1 6 t""

ry

m

t\a 1 N9 1 4

GPIA2

I

H'

Yoo

L2/14 15

I

H

F

2/4

5/6 2 Q / 3 D '7 /1-L 3a/4D L0/L3 4a/5D

|

|

|

|

(r

o

|

Il :

h r+! p,

L

o tv

Flgure fO-q BS2simulatorcircuit

S e c t i o nT e n S e n s o r s

225

0, fl rv

t+{

1.r {,

g H LI €,

&0

p

rq VJ rY1

rt .*

r 1

tu

basiccodewaswritten in C to take advantageof the codealreadywritten for the BS2two-wireinterface and the ADC (for the potentiometer),althoughthe tu7oBS2simulatedsubroutinesare written in assembler to ensurethe timingsare ascloseto the BS2'sas possible.As a referencefor the simulatedBS2,an oscilloscopewas usedwith the Parallax BS2 datasheets to make sure the signalswere aspreciseaspossible. *incluile - Sfu{rlated cBS2 Sl$.c /*

Bg2 Senso!

Interface

l,lria ProgEam Inltializes the Hltachi {{780 Baaett I|cD in { Bit Uoal€ a.Dd then coatinually !h€ lrotenli@r€ler oD cpIO2 as well Dolla aE the Button oo GPIO3. llhen the ButEon iB gress€al, th€ (Drocesa€tl ADC Value aE b€1o$) is Sent to another PIC lEU as if il wele a BS2 ComAnal. |Ih6 ADC value ADCValu€ ADqvaluo 0x07 ) t ADCVaIUe

is

proc€ss€d

as:

= (.a!RES >> 5) & 0x08, = ( (ADCtIalue & 0x08) << {)

PICSenil ( Ints DatavaLue)

{ //

Hex values

GPIOo - BS2 Interfac€ CPIO1 - B's2 Inlerface

Clock Pin Data Pi.n

IJCD Write Infor atiodr htstD: //w{w.rvk€.cd!

can b€ foural

Thls aDDlication uses arld PIC As6€nib1€r.

a cdnbiration

of

eiEher

of

andLw ttf btfsc iollw nol^rf

0x01-

PICC lJite

C

TSIS APPIJICATION USES tt'HE PIC15r675Ilt

GPIOs - I,cD Data Pla CGIOII - I,cD Cloch Pin

ig

qr

ce 4r ,tt

.t 1

&{ nl i,

& I'NPROIECT & BORDIS & !'!CIiADIS & -COIIFIG(T'NPROTECT P1IRTEN&IIDII'DIS&\ r$Tro) t int in!

IraatADc ButtotfLag

r'Ilsigrled ungigned uEaignetl

char cbar char

-1r - 0i

// //

€LastADCr ait aDlayt

taeb Italk // // //

I& value Reaat In Wlren Pre8aed

aasenbLer aasembler ass€rnbler

oL234557 490!2345 /t conat cbar rolabaaage II conat cbal BotsMaaaage I I = n Rea9onEe *defin€ Clk GPIO{ ll Defi-'ie the LD g€lial Control Pitr6 Data ePlos *defin€ // Lf Etj-ese Cha.nge, CharEe aesesibler cdrst

226

int

Tweftyrn5

= 1250;

tastADC Countor D€lay

3lrr _aLaEts.Al)c, status, 0 02h porta

r Clock Line iE Lort 5J + 256 t DeIaY l'!' 1,598 ua

/

5) + 256t

i

Shif,l

Outs the

Data

, Set GPIO1 t aDgrolrliale1y

f

iorllr 01h baf _a.DLay, 2 PSPTeIJooD: d'ecfaz f _a.Dlay, grolo PgPrelJoop [ovlrf Dortsa a*Uw 3dr baf, 2 _aDlay, PSCIockIJoop : tlecfsz f _aDlay, goto PSCIockIFop novllf Dorta rnovwf nqD PgPoatI6oIr

ryke prealko 04.n.23

0 Dorta, ((1688 lligh

novvrf _aD1ay novlw ldr ((1688 | PsgtartIJdqrDLay: -1 aaLlLw btsfsc statua, 2 al€cfaz f _aDlay, goto PsstartlJonDlay llovlt,r I rbvrff, ai PSOutsIoo9: lrdtrf, w Dotta,

&

a!

= Datavaluei alaatAllc gave ADc value tso S€nd

*asn bcf novLw

= .A.DgvaLue + 1t

ThiB wLl1 nsiufaclure 0:.08 or 0x81-0x88

NCIE:

= (ADCValue

a cdrstant f,or 20 nE Delay // Declate const irrts EiverDs = 300, con8! Ltrl TaroErmitr€ihrB = 10,

t ltlhia PoinE 14 cycl€s Clock Ei t befor€ t Set Clock Blts

t Sav€ Clock Eigh , Turn Off Cl.ock Aiglb

_aDlay :

, Data VaLiat fo! i ci'cles

al€cfaz goto alecfsz goto

f _aDlay. PSPoatLooD ai PSOUtloop

novlto

62

i R€Deat

i R€turn i af,ter

!rcvlrf a!1ay PsEndlonlLoop : alecfsz f _aDlay, golo Pstldrdlrl/ooD bsf 0 x,orta,

f,or

32

8 Cycl€a

Clock El.gh 188 cycl€s

Clock ia r Finally, Cqt!tr.rd Sent r High,

#eudasr ) // End PICSerd 0x00

n. in!

( ints Iratavalue)

PlcsebdRec€ive

{ //

aIJaatIDC = Dalavalu€t Sav6 ADC value to Senal

{iaEn bcf

9or!a,

0

l , a 3 P I C o l ' l C l JE x p e r i m e n t s f o n t h e E v i l

r Clock

line

6enius

ia

LoI'

hish ((168S / 5l + 2s6l ; D€LaY b!' 1'588 us nolwf alrlry low ((1688 / 5) + 256) novllr PsRslartsI,onDlay: -1 adaulr btsfac Btatua, 2 alecfaz altlay, f gotso PsRsltartldvrDlay rnovlw 8 o|rt the Data t ghift PSROUtsIJOOD : porta, novf

€natLw rlf btsfec iorlw rnovwf

bcf

3Dh _ar,a6tiaDc, atsatua, 0 02h Do!tsa

f

Point 14 ql'cleg r rhia Clock Ei r before , geE Clock Bit

iorlw 01h bsf 2 _aD1ay, PSRPrelooD: f tlecfsz _aD1ay, PSRPreLop Soto Inovlrf I)orta aDdlw 3Eh bsf _aDLay, 2 PsRclockl.ool, : d€cf,az f _aDlay, gotso PSRCIockLoop porta movwf

; After ; llata

0

porta, 1 btfac bsf atatuB, 0 rrf _aIaElADC novhtr 4 mov{rf _aDlay PSRlDoneIFop :

r Set GPIO1 r r*rDroD?iately

w

atatua,

seve

in

t Dala valifl t q!'cles

decfaz goto tlecfBz golo

f, aDlay, PsRPoallool) ai PSROutIoop

llov1v

high

f _aDlay, PSRPDon€IJooP

al€cfsz gotso

f _ai, PSRPoL!.Lop

rrcvlw

high

H"

fi.

+ 2561 r rinal

5l

/

5\

Clock

IJon D€lay

t Rel)eat

DaEa Pin

stsatus, 5 1 I)olla, slatus, 5

r !{ahe

baf

porta,

Clock is r rinally, CdrlEdril Sent r uigh,

bsf, bsf, bcf, novlcr

slatus, I)or!a, alatus, 8

blfBg goto bcf

for

8 cycLes

5) + 255\ t Po1I Response r 1.450 us

/ 5,

Buatsua, 2 f _aDlay, PsRPollDlaylooD

PSRPoUIJooD : bsf Dorta, noD rEvlw 3 PSRPHigbIooD : -1 atLl].n

//

letuln Return ll

lwbblesbift // shifr

*r{

0

i-"rl {. *t

(int T,Cf,iout, Ehe r,rybble

(

< 5r i++)

CLk = 1t CIk - 0i , // iof

Itata

Pin

PoIIing

r clock

Eigh

Re6Do(rse

to

q& i.,} iDl

Clear

//

,IuBt

,

lioggl€

the

Regiater

; *.*

Clock

| ((RS & 1) r (1 << {))t Shift Dala Out

(0 l= (LcDoul & (1 << s))) if Data = 1t // shift Bits Data = 0t LCDOut = IrcDouts << 1, Clk = l.t

PolI

tshe Sbift

!r-!i€

// //

tr! j

o{rt

th6

;

Eigheat

*-.!

Shift Up the Next Bit idto Clock the Bi! rh€ s/R

Clk = 0t // tof

i,J

rn d $

t Aftser

14 Ct'clea,

NoP()t

Clock

// lrovLw 5 PSRPWaitt ooD : aqp -1 aaLl]'trr 2 btfEa atatug, gotso PsRPwaitsloop

Iis)

//

LqDo|rt = Lcmut | (1 << 5) (i = 0r i < 5; i++) // for

Iaput

{ t start

r'rF9

8-rl

5

FtsatsuB, 2 PSRPHighIoop 0 DorEa,

our

Data = 0, (i - 0r i fo!

1

0

aIJaatADCt tsbe ReEponae

afte!

+ 256)

i llake

t

Outgrt

u\d. PrcsenalReceiv€

(

/

btfsc decfsz goto

5

32

s

i.''."

+ 255)

b8f bcf, bcf,

,

((1640

arovwf _aDlay abvLw low ((1840 PSRPollDlaylJoo9 : -L addlw

fo!

1."t

m n

to

*enalaam Dovwf aDlay nqD PSRPoatI,oop:

l*t

nalraalaDcn

, Delay {6 clrcleB t Ner.t Clock

Ilovltrf f _aDlay. movlw ].ow ((350 / PSRFina1T.oorr : -1 aaltllw statsus, 2 btfsc f alecfaz _aDlay, golo PSRFiIralI.oop

r Save Clock High r Elrrn Off Clock Eigh

PoI1

!r3 i

dlecfgz goto

((3s0

25 C:'c1ea,

tshe NybbLe clock th€ LCD

int

NOP(), Data = 0i

n!

r', gtl

|

//

B^d Nybbleshift

S e c t i o nT e n S e n s o r s

22'7

IJCDWTit€ (int |

{.}

int

a'1

//

r$

((0

if

i

.{*}

for

ICD

LcDwrite

( (LCDDaLa >> {) & 0x0F, Rsvalu€) (LCDDala & 0x0F. RSValue), // Shifl out ByEe

LCDWrite ( 0b1100000 0,

= llwollunalrealus

ai

r*

(i

= 0r

< ir

i

Delay

//

i++)r

for

character

(i

fo!

0,

//

!= 0, 1)t

i++)

!{ove CurBor to lhe Seconal lriae i++)

== 1)

//

-

0r

i

I.oop Through PoLliltg GPIO3 anal AN2

< Tw€nlt'mB, i++)t // BaEic Delay

fo!

ADc

main( )

int

i,

GPIO = 0b110011t Inlerface // gtsart with A.DCONo = 0b00001001i

ANSEI = 0b00010100,

CMCON = 0b00000111r oPTION = 0b011111!!t

Bits High // ADc Turneal on: ADI'U - left .tualifieal // VCEG - Valal Reference / / clls - aN2 // QO - Off // A.DoN - On // // ANSEI Specifieal as Tosc = Toac*8 // AN2 - Analog I/ laDut // Disable CofiE)araEor Uodlule // E':abLe pu11 uDs on RAo & RA1

wPU = 0b000011t TRISIO= 0b001100t // Everything Buts cPIo3/aN2 //

CiODoNE = 1t // Stsart ADC operatior == GODONE)t whiLe(1 j = (A.DRESH >> 4) & 0x0F, // Ploc€ss Usins ALgolithm Above j = ((j & 0x08) << {) + (j & 0x07}t j = j + a, (j t= LaatADC) if // If Different, Save antl DiEpLay

jt

8**,li

t-f

0)t

(

Enil LCDwrit€

//

itr,

f*; i, '; ".:i

lurD On LCD anal Enalrle Cursor

//

t

t

ry

0)r

(i = 0r BotMessaselil for IJCDwrite ( BotMessage t i l , while(1

)

( 0b000 01110.

f,or (i = 0r ToDU€a6ag€[iJ l= I.cDwrile ( ropMesaage t i l , 1)t

t

== (LCDData & oxFC)) && (0 == RsvaLu€) ) // S€t Delay ht.erva!.

".i

t,l

ints RSVatue) Sendl Byte to

j,

i.

NybbLeshift NybbLeshift

i.a-{

f-J

LCDDala,

Inilializ€ j = $tentlms for (i = 0r

< j;

i++)r

LaatADC = it // Sav€ the Nelr ADC Value LcDvlrite ( 0b10 0011OO, Ori /l Mov€ to 10a of OulDu! j = (j >> {) & 0x0Ft High Dtgits // wrile LCDWrite (J + t0', 1)t IrcDwrite ( (LestADC & 0x0F) + r0., 1)t ll fL , ((0

if |

to

the

W€b page

Wait fo! LCD !o power UP

//

-= GPIO3) && (0 == BuEtonalag) ) / / Debounce Buttoa

Press

(i < Tnenltlma) whtle (i = 0t (i < lw€ntt'ms) && (0 -- CPIO3); for i++) t = 1r But.tonFlag Pr€sseal // Button (ra3ta.Dc < 0x60) if PICSenaI (IJaaEADC) t else // Get Remo!€ Statua/Va1ue

OulDutsa

IJCD accoraling t i

t

t N1'bbleshifl(3,

1 !

q*4

i!"!

+-] ;^,i

ti

s

. r''.:l i$t

j

0)r

= Fivemst fo! (i = 0r i

< jr

(3, 0), Nybbleshift j = TlroHultlrealus t fo! (i = 0, i < j, (3,

lwbbleghtft

lrybbl€shift

(2,

RegeaE ReEets Cdmand

i++)t //

Repeats Reset Thiral Tlme

Cqrdnanal

i++),

0),

j = TwoHuntl!€alu€ t fo! (i = 0r i < jr LcDwrit€

//

0),

j = rlroEundlrealus t for (i = 0, i < j,

( IJastADC ) t LaatsA.DC = PlcgenalR€ceive LCDWrite(0b11001100, 0); j = (IJaatADC >> 4) & 0x0Ft High Digit /./ Write tf (i > e) rrcDwlire ( j + ra' - 10, else LcDwrite (j + .0,, 1), j=laBtaDC&0!.08, // write r,ow Digit i f ( i > 9 ) I J c D W r i t e( j + . A ' 10, 1)t eLse LcDwrit€ (j + '0,, 1)t // ti , ((1 == gp1g31 && (1 == ButtonFlas) ] else if ) ReleaBeil | // I,ook for Button i = 0t (i < Trreatt'ns) while (i = 0, (t < Tw€ntldrs) && (1 == GPIO3), for i++) t = 0t ButtoaFLag Releaaeal // Buttoa

Star! Initialization Ploeeag // gendl R€set Conmanal i++)t //

//

rniEiau.z€ l4oat6

rJcD 4 Bit

i++)t

( 0b001010 00,

0)r

//

LCD is 2 IJlne

IJCDwrite(0b00000001,

0) t

//

clear

IJCDwlite(0b00000110,

0) t

//

Move Cufao! After Each Charact€r

4 Bit

I/r',

| r,cD

, I

i;i

// Er

/ / eri}lw / / E'l,d cBs2 sin

f-.tl

228

l , a 3 P I C @l l C U E x p e r i m e n t s f o n t h e E v i l

6enius

The assemblylanguageusedin cBS2Sim.ctook longer than I would have expected,this was due to two factors.The ffustwasa mistake on my parl I did not disablethe comparatoron the PIC12F675'sGPIO0 and GPIO1 pins (usedfor the BS2 interface),which I discoveredoften resultsin unexpectedresetting of a pin when wdting to a singlebut different pin. In Section 8,I went to geat painsto explainhow the bsf and bcf instructions work, and, in this program, I ended up with a great exampleof how they can unintentionally changea pin value. In my applicationcode,I set the data pin (GPIO1) and then I thenset the clockpin (GPIO0),usingthe standardinstructions: baf bsf

GPIO, GPIO,

1 0

but whenI looked at the signalson an oscilloscope, I sawthat the data pin (GPIOI) would go low whenthe clock pin (GPIOO) wasset high.When I wrote the application, I wasunder the impressionthat the PIC12F675had an ADC but not a comparator,but I waswrong. Like the PIC16F684,the PIC12F675has a comparator with its input pins being GPIO0 and GPIOl.And like the PIC16F684, if the CMCON register is not written to turn off the comparator at power up, thesetwo pins are assumedto be analog inputs (which alwaysreturn zero when the port register is reador usedby the bsf instruction).OnceI tumed off the comparator,the pins behavedasI expected them to. I'm explainingthis becauseifyou had an applicadon that didn't work or if it behavedasmine did, you might be inclinedto assumethat the PIC MCU chip wasbad.Rememberthat you shouldalwaysassume

first that the chip is good and the problem is software related,aswasthe casehere:I didn't properlyinitialize the chip.Assume secondthat your circuit/wiring is bad. Over the 10 yearsI've beenworking with PIC MCU chips,I've encounteredonly two chips that were bad. The first time was when I waswiting Programming and.Customifing the PlCmicro@Microcontroller,in which I seemedto have worn out the Flash program memory of a PIC16F84;severalinstructions could no longer be programmed.The secondencounter happened when I was debuggingthis application and I miswireda PIC16F684inshumentapplicationto this BS2simulator;I accidentallyconnectedthe BS2simulator's ground to the instrument application's positive power.AAer correcting the error, the instrument application would work periodically,but required a special sequenceof actionsto get it working.(I had to power up the instrument application first, next power up the BS2 simulator, then disconnectthe two applications, and finally reconnectthe applications) Pro$amming another PIC16F684with the sameapplication did not require any of these actions and would, in fact, work perfectly regardlessof which PIC MCU application waspoweredup first. The root causeof this problem wasthe use of two breadboardcircuits,eachpoweredseparatelyand connected by three wfues(two for clock/data and one for ground) asshown in Figure 10-5.This connection reflectshow I wantedthe BS2simulatorand the instrumentintedaceapplications-eachasseparateas possible,havingonly the signaland gound reference in common.If I were using this application for anything but prototyping,I would createpolarizedconnectionsthat couldnot be pluggedrn error.

f{l lr,t a1

ru tv

Ft 1..

3 tv !-i

CIo #t I I

ry H

n K

n

u,

U) h,)

m tn

$ H 4

1n tl

r.h sl (l fn

S e c t i o nT e n S e n s o r s

229

AI

ri rrt

Experiment B5-Plf MEUB5a KegpadInterface

s{ &,

Prc16F684 1,5-button face

b'{ d

keypad

inte!-

1 fwo-Iine by 16-character LCD display

i

1 10k breadboald-mountable potentiometer

T {'d

Either

1 10k 10-pin

Or 810k

:&

SIP

resistors

1 0.01 pF capacitor

a!

1 SPSf bleadboard-mountable switch

DMM Needle-nose

pl iels

1 Three-celI clip

Breadboard Wiling

kit

AA battely

3 AA batteries

"i'ta

F I q: -':

.'l

',

t^-]]

a'l , :

i

.i1

a'-r fi -.:

r-: s:,11 ai.. fi.1. C'.t,{ !-*1

Although the potentiometer-controlled PIC12F675 interfaceworks well,I wantedto seehow easyit would be to createa keypad-controlledinterfacewhile at the sametime eliminatingthe needfor the 74LS174used asa shift registerfor the LCD display.Pin allocation can be difficult in this situation.A four-by-four(16-button) keypadrequireseight I/O pins;an LCD requiresa minimum of six if the two-wire shift register is not used;andto top it off, two wiresare requiredto provide the BS2interface.The total number of pins requiredfor this applicationappearsto be 16.However,asI will show,the keypadcolumnand the LCD datapins canbe shared,allowingthis applicationto be wired into a singlePIC16F684with only 12 I/O pins. The trick to sharingpins in an applicationlike this is to look for output pins that canbe sharedbetween interfacedevices. It shouldbe obviousthat clockingor control pins cannotbe sharedbetweeninterfaces,as the devicebeingaccessed will be confusing. The LCD datapins and R/S pin canbe sharedwith the four column drivers usedin a four-by-four switch matrix keypad.The combinationof thesetwo componentson the samedatabits worked very well with just a coupleof complications. For this application,I wantedto keep the LCD data pins on RC3:RC0to simplifythe programmingof the LCD writes(keepingthe databits in the lower nybble of a byte).And I alsowantedto keepthe wiring assimDleasDossibleon the breadboard.Thesetwo condi-

230

tionsweremet (seeFigure10-6),althoughit wasdifficult to showthe simplewiring to the keypad.The schematicmight be a bit confusing;rather than draw the rowsand columnsof the keypadasfour individual wires,I useda bus,which is a thicker line.Thesefour linesare passedto the rows and columnsof the keypad asshown:The keypadI used(boughtfrom a surplus storein Toronto)had the rows and columnsin two groups of four pins,which simplified the breadboard wiing for my prototype. Note in Figure10-7,the four columnbits (the bus linesthat intersectwith the LCD bits) do not useall four LCD databits.Insteadthree data bits and the RiS bit are used-asthis worked bestwith the breadboard. This made the software a bit rnore complex but was worth it, asI did not haveto wire eachkeypadpin individually to the breadboard/PlC16F684. InsteadI could simplypushit into the samecolumnasthe pin-1 sideof thEPIC MCU. In the apptcation,I pulled up all eightpins of the keypad.Like whenI startedthe application,Ididn't know which pins were which, and I had to decode them.When you look at the sourcefiles for this application,you will seethat I createdasmsctrll.asm throughasmsctrl4.asmto decodethe keypadand make surethe operationwas(reasonably)intuitive. The final result.asmsctrl5.asm.takesin a maximum two-hex number command (taking advantageof my keypad's2ND key,which I usedto shift the key inputs

l , e 3 P I C @l l C U E x p e r i m e n t s f o r

the Evil

6enius

Fiqurel0-7

BS2 Fiqure l0-6 Breadboard-wiredkeypad-based breodboard simulator wiretl tr.tsensor

of 1 through6 to A throughF). The CLEAR key was usedto erasethe two-charactercommand,and ENTER sendsthe command(and,if the valueis 0x80 or greater,it alsolooksfor a reply). Dependingon the keypadyou usefor this application, you may not be ableto wire it assimplyasI have

Keypad BS2

for my prototypeor the keyson your keypadmay requireyou to work out a differentuserinterface. When you createyour own keypadinterface,follow the stepsthat I have:First,get the LCD working;next, work at decodingthe keypad,and model the user interface;and,finally,add the B52 interfacefor the peripheralfunctions.You will probablyfind that working throughthesestepswill take you a few days,but they shouldbe fairly uneventful,and whenyou haveto perform this task againlater,you'll find that it will take onlv a dav or so.

86-PlC MfU lnstrumentInterface Experiment

1PICl6F684 1 LED 0 .01 pF capacitor fhree-ce11 cli p

AA battery

AA batteries

P I C 1 2 f 6 ? 5 o ! P I C 1 6 F 6 84 based BS2 coBnand interface sinulator DMM Needle-nose pliels Wi!e strippers Breadboard Wiling

With the BS2and PIC MCU equivalentintertaces available,we cancreatea simpleapplicationthat turns on and off the LED connectedbetweenRA4 and RA5 of a PIC16F684remotely(seeFigure10-8).Thisexperiment hasonly threecommands:(1) LED On, (2) LED Of| and (3) 0x81- Return LED State.And its codeis basedon asmBS2Template.asm:

kit

5 e c t i o nT e n S e n s o r s

23t

$g t

RAO

I BS2 J Interface

RA1

ftt

wl

tr

cnd

t R€giatser usag€ CBI|oCK 0rr20 t i, j, k Bg2Btrtse , Dlayvalue:3 r t ENDC

RA5

Plct6F684

p

liat R=DEC INCTTTDE'p15f 58{. incn

Sgart

of

cP R€gistela

Bg2 Senal/R€ceive Value lrhree ByEes Neetleil for Macro

D€1ay

0-J PAGE

-T; .5 V

#

_coNFrG ,E C!{EN_OEF & _rESO_OFF & BOD_OrE & & PIVRTE Oll & _qPD_OFF & Cp_OrF & _!{CLRE_OF! _wD1!_OFt' & IN:IOSCIO

I _t_ :

fil

Figurel0-8

BS2Demo

t [qaiDline

;J iJ

s

"asr8s2

Eitl€ llcu Intelfacer

t},t

This Program Drovidles an Intelligent BS2 Interface.

t; *,1

f l

r*r t

r{ F,ed

a t

\s ffi

the

BjISIC

baaia

StarD

II

for

Bs2 CorElantla (tso be ilefineal by applicalion) 1 - CdmaaA 1 2 - Comland 2 3 - Cdmanal 3 4 - Codmanal 4 5 - Cormand 5 6 - CoduEnal 5 7 - CodEranal 7 I - CoiElantl 8 (to b€ tlefined Data R€aDo[al Coltnanala by agl)licaEion) 128 - ResDoutl CorElanil 1 129 - ReaDonal Corrlanal 2 130 - ReaDoail Cortrlanal 3 131 - ReaDonal Cotunarrd { 132 - ReaDondl Cor@aaal 5 133 - R€6Donal Colulanil 5 135 - R€sDontl Comtanal 7 135 - ReaDonil CofinenCl 8

f-1

1

T€!!p1ate

-

llaralware No!€a: t PIC15F684 runnLng at { UHz Uainq th€ r Inlelnal Clock r Int.elnal Reaets is Useil r aAs - Clock hput t ltA4 - Data I/O t Renaiaing Pins a!€ for VariouE t I/O atrd Fullc!ions

pIC

o!9 no9

=i*fi € r

i , ,

ConData Comclock

Uyke Proalko 04.LL.25

PORTA, 1 PORTA, O

i

trovlw

0x0Fr

movlrf movhr

PORTA 7

rnovwf baf clrf

Cllcolro STATUS, RPo ANSEI, ^ 0x080

bcf

OPTION_REG ^ 0x90,

movld

b'000011'

For

r Make , BLta

; r 7 , i r r

All PORIA High

mov$f WPUA | 0:rg0 #*l+# - uoatj.f,ylPut 1n Aalditional t Bil/PeriDheral Initializations bcf SIATUS, RPo lrooD waitiag fo! r IJooD: btfsa Cdclock caLl **** t oDelation8 goto

AlI Bils a!6 Digita]' Eneble PORTA pull UI)E Enab].e RAo/RA1 Pull U9a Porl

BS2 corEEndt i Reaal BS2 Eor t Codmanal

BS2R€aal P€rfofir here IJooD

Reatl/R€apoaal ; BS2Reaal:

aDy Repeating

to

gub-ns

BS2 Comlanala i D€coale tsb€ BS2 t CorEraad i Mrnber of Bits i to Reaal

i

movlw rrrcH (3800 + 255) movwf J movle LOw (3800 + 256) as2RlrooD].s

r Wait for Data to t becdne Active

&d

232

ICD2

t qodE)arator8

lnovwf, *alefln€ *alefia€

0

l , P 3 P I C o I ' l C l JE x p e r i m e n t s f o n t h e E v i l

6enius

btfsc golo aflilhr btfsc decf.z goto

comclock BS2RSkiD3 -1 STA!!US, Z j, f BS2R]JooP1

i coun!

BS2RE!ro!: S!!ATUS, RPo CdlData

bcf reEur!

STATUS, RPo

blfEs goto dl€cfsz goto goto

i i i

, i t i

r Clock LowlReatl r the Data Bil

il,cf .z golo

i, rd BS2RSkip2

btfBc

BS2B!rt€,

r sbift

in

the

.i at the rJest - No... i 7

Bg2RReaponflcdmanal

i Bg2 R€sDondl t C@land? i.f No, wait t

i BS2RSktD2:

Final

clock

Bj.t Bits?

for

Eigh

, Clock StiU , Low/Wail f,or High 100 j r wait 500 pE for r Clock EIgb

BS2RIJOOI'2 : CoitrClock BS2I€kips j, f. BS2RLoop2 Bg2Rlirlor

BS2RShLps:

goEo

Retuln

Cdclock BS2RSkiD{ j, f Bs2RLoop3 Bg2RElrol

STATUS, C C@Data STATI'S, C BS2Bl,t€, f

al€cfaz

Datsa

t Wait 15 Fs for t Clock Pu1ae i Activ€

bcf btf,sc baf tlf

btfac golo tl€cfEz goto goto

Meke gure i5 Iry)ut

4 j

BS2RSkiD4:

novlw movnf

Valial

wail t Clock High, it lo qo ].ow i for

BS2RSkID3 ! novlrr novlrf BS2RLoop3:

Down

, Nothlng i R€ceiivetl

baf bsf

nop r.or1w btfBc no9 r{or1!r btf,Ec noD *or1w blfac nqp xorlrd blfac trqp xorlw btfac aop xorlw btfac nop goto

,,

f

r r r t

Clock High Agai!/finishetl with Bit Reaal Anothe!

t t r t t

Cbalge tsh€ Cd[larrtl ODoralion GeE the co@anil Cd[)are tso C@lanal 1

ES2RSkiD3

BS2Prj.rnarl|c@lanal: nrovf :
Bs2Btztse, 1

w

btfac no9 xolIrr blfac

STAIIUS, z - comnand t **#* 2 ^ L SltrAlrOS, Z

1 code t Coraltalal

2?

- Cof@and 2 Coale , **## 3^2 r Corl.rtt STA!!US, Z - cofdland 3 Coale t **#* l^3 r Cdmantl STATI'S, z - Cdmand 4 Cotl€ t **#+ 5^{ , CdmtDtl STAIrOS, z - Cddand 5 Coile t **** 5^5 r Cdmand SIeTUS, z - cdmand 5 cod€ t ##** 7^6 t Cdirnendl gTAmS, z - Cqflranil 7 cod€ t ll**{l 8^7 ; CdmanA STITUS, Z - Colnalat 8 Code r #**ll Bg2$r!or Itnklownlcodlrl€l€d t otherrdLa€,

- Pu! coulalit Eele with t\rDctioas **#* "gtoto Bs2RErlor" to junDa ov€r evoidl havlng funat' **** "switsch" corqrariaoDB asseribl€f

tcl X

3?

id

{?

o

r-t

5?

F,,

6?

3 o

7?

5 cl

8?

coiMenat Filel

BS2RResponalcddandl : lrilbin Ittforllation Retuln lhe R€questseil t 1 lrE to "BS2B!r!e" i anfl rrgoto BS2RResDondl: i bsf STATUS. RPo i llak€ ConData aa OutsDut bcf ComData bcf STATUS, RPo w novf Bs2Btte, t Get Eb€ cor@r'otl lo R€apontl laor1w 0x81 i Corltrare 1 t C@raad btfac SrAtUS, Z - R€a9ond Codrald 1 Coal€ noD r *##* xorlw 0x82 ^ 0x81 i CdE ar€ to Responal 2 t CdEand srATtrg, z btfsc 2 codl€ nqp t *#*l+ - ReEDontl cdalanfl xor1$ 0xa3 ^ 0x82 r Collpare to ResDordl t Co!trranal 3 btfac SllAllUS, Z - ReEDolal Conlanal 3 Coile aop t **** tso ReaDondl xorld 0x84 | 0x83 i Cot[tale 4 , CotElald gfATUS, Z btfsc tro9 CotElend { Cotl€ , #*## - Iteapoait to ReaDonal xorlw Ox85 ^ 0x84 i Codpare 5 t cdrland gTATgg, z btf6c 5 Coale noD r l+lf #* - R€apond C@lantl ,ro!1w 0xg6 ^ 0x85 i CoaE ere to ReaDoatl t codnnenal 5 gIATttS, btsfac Z - ReEgonit C@lanal 6 Code noD r li#*lf xolLw 0x87 ^ 0xg5 t CorqDare tso Reaponfl 7 , CoMlantt blf,sc STAEUS, Z - RealtoDd Cotnaatl 7 Codl6 Dop , ***# *orlrd 0x88 ^ 0x87 i Coqpar€ to R€apond g t Cdmand btfEc aop lrovlw

STATUS, z - Resgond Cdmanal , **** 0t 15 r C@la|rfl

I

Coale Not

O

o\

I ry H

o K

o

c H

p

a d l-t

6

I o p

ct H

p

d

o

rt

Fh

0,

o o

5 e c t i o nT e n

Sensors

233

G,}

movwf

BS2BtrUe

d

golo

Bs2RR€sDonal

{r a }{ ,it

IJ

4J ;J F{

l-a

Bs2RReEpondt: rnovlw 8

novlw novwf lrovl.w Bs2Rr,ooD4: btfsc golo aaLllw btfsc alecfBz golo gtoto Bs2RgkiDS: rrf btfsc bsf, btfsB bcf, movlrc movlrf BS2RLoop5:

U s g.i

btfaB goto dlecfaz goto golo

r*; BS2RShipT: r--N nrovlw novwf & rrovhr I I In

BS2RError

i i

ghow

to

FiniBh€tl, anal Keep

Retutn Proceasing

€nd - Execute ***# RegDontl cotElandts t Executso ldithL! 1 rns

novwf

L'

goto

; Supgortodl t Bi! Pattern t coanection

gt

CounE Nunber Bita to sentl

To operatethe applicationcode,I modified asmBS2 Ifasm to get asmBS2Test.asm by makingthe following changes:

of out

i

1.

HIefl (2500 + 255) j low (2500 + 255) for Deta i wail becdre Active Cqlclock BS2RSki95 -1 z STAmg, j, f BS2RLoop{ BS2RError

BS2Byle, STATOS, C CotnDala STATUS, C CdDaEa

f

2. to

3. 4. 5. Bits Bits

6. i

Deta

Bit

Higb

i

Data

Bi!

Lor,t

"ComClock" and "DataClock" were changedto RA1 and RA0, respectively, For "Command l," replacethe nop with "bsf PORTA,4." For "Command2," replacethe nop with "bcf PORTA,4."

lhe Data i OutDut t Put the LS Data into calry

4 j Wait 15 ma€ca fot Clock PuIa€ Activ€ Comclock BS2RSkiDT j, f BS2RLooD5 Bg2REfior

The xor*{/btfsc/nop instructions for the remainingsix commandswere deleted. For "RespondCommand1," the "btfsc STATUS, Z/nop" wasreplacedwith a "btfss STATUS, Z/goto InvalidReturn."And the following xorl btfsc/nopinstructionswere deleted. After "goto InvalidReturn,"the following instructionswere added:

novllr btfac {rovlw novwf goto

O

,

novwf

BS2Bf.le

Wait fo! to Enal

Hrclr ( 3 0 0 0 + 2 s 5 ) j rJow ( 3 0 0 0 + 2 5 5 ) wait 3 na for High

clock

Codclock Bs2RskipS -1 SEATUS, z j, f Bg2RIJoop5 BS2RErro!

BS2RSkiDS: alecfaz i, f golo Bs2RSkiD5

i uor€ i

Bit6

to

S€nal?

Yea, IJooD Aroundl Aqain

R€lurrt

i

CorE|anal Not gu9port6al

i

Bit PatEertr CoDn€ction

to

Sbow

With thesechangesin place,the PIC12F675tnterface connectedto the breadboard with the circuit in Figure10-8,and the PIC16F684loadedwith asmBS2 Test.asm,you can nouTremotely tuln on and off an LED aswell as query the LED's state.To turn on the LED, set the PIC12F675interface'sLCD to 1 and pressthe button-the LED connectedto the PIC16F684shouldtum on. Similarly,settingthe PIC12F675ntertace's LCD to 2 will turn off the LED. Settingthe PIC12F675interface'sLCD to 0x81and pressingthe button will senda command responseand retum zero or one,indicatingthe stateof the LED connectedto the PIC16F684.

.r{ 9 , . ,i!

4",S

234

r,ED gtatse

PORTA, 1l 1 BS2Blrte Bs2RReapontl

hvaLidlRetur!: novLw 0xA5

BS2RIJoopS: btfsc goto etLllw btfsc decf,az golo goto

- MusE

l , e 3 P I C @l l C U E x p e r i m e n t s f o r

the EviI

6enius

krt

t-J

Experiment87-Sound Detection

Prc16F584

;;e" *{

TLC251 LED Elect!et

1v

miclophone

3.3M resistols 2.3M resistols l,ok lesistot 470O resistors PIC12F575- o! PICl5F68 4based BS2 conmrand simuIator inte!face

220O resistors 0.1 pF capacitors 0 .01 ,pF capacitors

DMM NeedIe-oose plie!s Ili!e

stlippers

t r!

Breadboard Wiring

t i

kit

:iSoundinput recognitionis an interestingand often usefulsensorto add to your applications. With just a bit of signal-conditioning circuitry,you can add the ability to recognizesoundto the PIC MCU. Before you start gettingvisionsof addingvoicecontrol to differentelecffonic devicesaroundyour house,I mustwarn you that the circuit usedin this application is quite rudimentary and will not recognizesoundsof differentdurationor frequencies. What you'll get after building this experiment is the front-endcircuitryusedin the "clapper" light switchesthat were popular a few yearsago. The applicationcircuit in Figure10-9is probablya bit more complexthan you would haveexpected. Along with the PIC16F684with its BS2 sensorcontrol interface,I have also included an LED, which flashes when sound is received,and a two-operational-atnplifer (op-amp)circuit,which is usedto filter out highfrequency sounds(defined asanything above 340IIz) and amplify them to useful levels for the PIC MCU to recognizeaslogic level changes.The circuit fits easily on a smallbreadboard(seeFigure10-10).However,if you wanted to add any additional circuitry to the experiment,you would haveto usea largerbreadboard.

I don't want to go into a greatdeal of explanation aboutthe operationof the TLC251op-ampsexceptto explaintheir basicoperation.I shouldpoint out, however,that the componentvaluesare criticalto correct operationof the circuit.If the resistoror capacitorvalues are changed,you will find that different parts of the circuit may go into oscillation.You shouldbe particularlyconcernedaboutmatchingthe impedanceof the electretmicrophoneto makesurethat you maximize the voltage output. If you feel the need to change any of the component values,make sure that you understandthe ramificationsof what you are doing. The electretmicrophoneproducesa relatively small-scale signal(in the tensof mV, asseenin Figure 10-11).Thissignalis passedthrougha dual-poleButterworth low-passfilter, and then amplified an extreme amount.The amplification factor usedin this application is on the order of ten thousandtimes for eachopamp.The reasonfor the extremely large amplification factor is that this application can amplify the signal only to the input voltageextremes. Anything greateris clippedandproducesthe signalseenin Figure10-11. The signal from the microphone is the analog signal shownin the top waveform. By amplifying the signal

S e c t i o nT e n S e n s o n s

235

t{!! 1 a : !;a i i

r& { }

vdd Ptct6F584 RA1

RC4

RC5

J.2 5

Data 1 l

(_L -

t

,'04

Clock

RAO

vdd

TLC25'I

470 3.3M

,s

rF-l .e :

vdd

0.01uFI

TLC251

-T; .5 v

lI :

I

ft '(jt '$i

t-"1 $,4

Figure l0-9

Soundcircuit

by suchan extremeamount,the more digital-looking signalis producedand canbe passedto the PIC16F684'S input directly. There are rrany books available that will explain the operationof op-ampsin greaterdetailthan I will here.Whenyou look at thesetexts,you will seethat

a

t

most of them usethe LM741,not the TLA57 that I usedin this application.I did not usethe LM741 in this applicationdue to its requirementof at least12 volts to operate.The TLC251 works comfortably with the 5 volts usedby this application. There is one problem with this circuit: If the sound transition occurswhen the BS2 interface is communicating with the PIC16F684,the PIC MCU cannot poll the incoming sound line. When I presentedthis circuit tn 123Robotics Experimentsfor the Evil Gmtus,l passedthe signalto a14LS74D-flip-flop clockwith

a-li I

.&r flt "r{ 1 !d{

gsi

Figurc lo-'f0 Soundinput testcircuit buih on small breadboard with BS2 command interfaceproviding signalwiring as well aspower

236

'f Figure 0-ll

l , e 3 P I C @l l C l J E x o e r i m e n t s f o r

Soundoperation

the Evil

6enius

the expectationthat the soundwould causea new value to be latched into the flip flop. To avoid this requirementnow,I passthe conditionedsoundoutput to the TMR0 input pin. Then, after setting TMR0 to OXFFand resettingthe TOIFbit to find out if soundhas beendetected,it is a simplematter of checkingthe TOIFbit asI do in the experiment'sapplicationcode, asmSound.asm.

The simple ability to recognizethat a sound has happened(evenwithout the sound'scharacteristics) canbe usefulin a varietyof differentapplications, rangingfrom the "clapper"to a robot'scollisiondetector. The collisiondetectoris actuallya very usefulsensor in robotsand often more reliablethan whiskersof the infrared (lR) or ultrasonic methodspresentedlater in this section.

I --l .'r|

lt't 1U ,<,

,1

g Experiment BB- Multiple Microsuritch Debouncin

ai-

& G8 1Prcl6F684 a

4 10k res istols 1 0.01 pF capacitor 4 Bleadboard-mountabl.e or SPST push-buttoo switches

PICI2F6?5 or PICl6F684based BS2 cofimand sirnuIator inte!face DMM Needle-nose

pliers

Wire strippels

pins on PORIA, but decidedagainstit when I looked at how I would poll and debouncethe buttons.Instead, I usedthe leastsignificantfour bits of PORTC,allowing me to come up with an efficient method of polling and debouncingthe buttons.Theapplicationitself can be written out in C pseudo-code asfollows:

B!eadboa!d Wiring

?

H. t*J

tv

?

j = 0t (1 == 1) whil€

kit

(

Previously,in this book,I haveshownyou how to debouncebuttons,switcheqandkeypads(in both C and assembler).What I havenot doneis showhow multiple,independentswitchescanbe debouncedin an environment that can be polled periodically. In this experiment,I will usethe BS2comrnandinterfaceperiodicallyto poll a PIC16F684wired with four buttonsor switchesthat mustbe debouncedbeforea valuecanbe retumed.Thisis very similarto what would be donein a robot that hasseveralwhiskersaroundits penmeter. The circuit usedfor this experiment is quite simple andcanbe built on a smallbreadboardwted to a BS2 commandsimulator-either the PIC12F675usinga potentiometercommandselectionor the keypadinterface(seeFigure10-12).WhenI wasdesigningthe application,I debatedwhetherto usethe pulled-up

// //

// //

// / /

for (i = 0t i < 215 usi i++)t I.oop takea 250 ua (0 == BS2Clock) if Clock Lotr' - ES2 Cofidland BS2Read( ), (0 == (PoRrc & ( 1 << j)), if Bit i-a IJow (0 == value ti I ) if Blt vas P!€viousLy IJow (Count. [j I < 20] if Counts=Count+1t elBei Count == 20. Do Nolhing elBe BiE $ae Pr€viou61y High

h*

t

ra

valuetjl = 0, Count [j I = 0, j ll fr elae // Bir iE high if (1 == valueljl ) High / / B..E vae P!€vloualy if (counttjl < 20) count=count+1i

ii,

1.3 ?.t

l-r '

S e c t i o nT e n S e n s o r s

237

elset == 20, Do Nolhing count else Eow // Bit vraa Previoualy //

{ va!.ueti] counutil |

//

= 1t = 0t

fI

j = 6 + a l % 4 t j to next // Increment // elihw )

value

In this2507:.is loop,one of the four switchesis polled,and if its valueis differentfrom the previous poll, the new valueis savedand the counteris reset.If the valueis the same,the counteris incrementedto 20. With eachloop taking 250ps and executingfour times betweenpolls,a count of 20 will meana 20 ms debounceperiod.The216ps delayloop,when added to the 34 g.spolling codetime,resultsin a 250pcsloop. The assemblycodefor this operationcanbe found in asmUSW.asm. This codecouldbe expandedquite easilyfor more buttonsor reducedasrequired.(Six couldbe made availablequite simply,by addingRC4 and RC5 to the

Figurel0lP

B32 uSwitch

four alreadypresent.)The codeexecutesin just a few instructioncycles,allowingyou to add additionalsensorsor BS2functionsto the mix quite easily.

Experiment 89-Light 5ensors Ple!n[t"

1 1 Prc16F684 L0k resi stors 10k light resistors with light

dependant (R decreases )

10k potent iometer 0. 01 pF capacitor

Tool

Box P I C 1 2 F 6 ? 5 o r P I C 1 6 F 6 84 based BS2 comnand simulator interface DMM NeedIe-nose pliels l{i!e

strippers

Breadboard Wiling

kit

In the previousexperiment,I showedhow you could time sharebetweenoperationsto checkvalueswhile polling for BS2commands.Inthis experiment,you will get the chanceto experimentwith differentwiring of

238

light-dependantreslstors(LDRs) or Cadmium Sulfide (CDS) cellsaswell asIook at a methodof reading eachADC individuallywhile polling for the BS2commands.Thismethodof operationis not compatible with the previougbut either the microswitchpolling methodor the one in this experimentcouldbe modified to work with the other. To demonstratethe operationof the CDS cells alongwith how the ADC works for multiple devices,I usedthe circuit shownin Figure10-13.TheSPDT switchshowsthe high- and low-voltagelevel provided by a simpleswitch,and the LDR connectionsshow how the voltagedivider output voltagechangeswith the LDR resistancevalues.Thein-circuitpotentiometer shouldwork exactlyasyou expect.Thatis,the

l , e 3 P I C @I ' l C l JE x p e r i m e n t s f o n t h e E v i l

Genius

ADC valuereturnedfor the potentiometeris proportional to the positionof the wiper. The applicationcode(asmlight.asm)for the experiment is very straightforwardand readseachADC valuetwicebeforesavingthe value.Readingthe value twiceis simplyto ensurethat the valueto be readis correct.Thecodeis calledasmlight.asm.When you test this application,you shouldrecordthe ADC valuesfor the LDRs whenthey are exposedto ambient light and againwhenthey are shieldedfrom the light by a finger.(TheADC valuefor the LDR connectedto Vdd shouldgo down and visaversafor the LDR connectedto the circuit'sground.) The applicationshouldwork quite well,with only one possiblesurprise:Youmay find that valueof either the high- or low-voltagelevel returnedfor the SPDT switchis off by a few digits (a valueof 0xFFor 0x00, respectively, is expected).Thisis due to resistances throughoutthe wiresand breadboard,which cause smallchangesin the voltagesat differentpointswithin the circuit (a singleADC digit represents17 mV in this application).The reasonfor pointingthis out is to rein-

Ptc16F684

":_r 6".+,,,. -o:i

{"-1;

II

I

.5 V

Figure 10-13 BS2 light

: force the idea that nothingis absolutein electronics circuits,and you mustalwaysdesignyour circuitry and softwareto accommodatetheseinconsistencies.

Experiment90-lnfrared (lFl)SurfaceSensor

1 PICI6F584 1 2N3904 NPN trans istor I

U-shaped IR opto-inte!(see text) luPter

L LED 3300 resistors IOk resistors 1 0.01 gF capacitor DMM

1 Breadboard-mountable SPDT switch

Needle-nose pLiers Wile

clj.ppels

Three-cel.1 clip

Wire strippers

AA alkaline (see text )

Breadboa!d Wiring

kit

In 12j RoboticsExperiments for theEvil Genius.I demonstrateda basicline-followingrobot usingtwo cut-apartU-shapedIR opto-interrupters. If you look backat thoseexperiments(numbers48 and 119in that book),you'll seethat by cutting apartthe two halvesof the opto-interrupterand placingthem sideby side,you

AA battery batteries

could make a fairly effectivewhite/blacksurfacesensor.Theproblemwasthe cfucuitsrequireda fair amountof supportcircuitrydue to the requirementsof amplifyingthe currentfrom the opto-interrupter's phototransistorand comparingit to an expectedvalue. The built-in comparatorsof the PIC16F684allow you

S e c t i o nT e n S e n s o r s

239

:. .,:

to simplifythe circuitryconsiderablyasis shownin Figure 10-14.With just a few resistorsand a transistor,you canproducea voltagethat canbe sensedby the PIC MCU and canbe coupledwith surprisinglysimplesoft ware. Thesepartsgo by a varietyof names,including "slottedIR opto-interrupter"and "IR switchOptoNPN" if you werelooking in a catalogor online,be sureyou seea pictureof what you are getting,because the devicesvary widely.Another issuethat you should be awareof is that if you wereto buy the pa s from a distributor(e.9.,Digi-Key,Mouser,Jameco),you'll probablybe quite shockedat the price,especiallyconsideringI'm tellingyou to cut them apart (seeFigure 10-15).Thereare alsoIR reflectivesensorsthat perform the sametask asthe cut-apartopto-interrupter,but thesetoo canbe quite expensive. Rather than be subjectedto the high pricesof new opto-interrupterEI buy a few from electronicssurplusbins for a just a few centsapiece. Buying the partsfrom a surplusbin meansthat you will not havea part numberor a datasheetfor the part. Instead,you will haveto build a circuit like the one in Figure10-16to determinewhich set of pins are for the IR LED and which set are for the IR p hototransLstor (PT) that makeup the opto-interrupter.Assumingthat the wiresfor eachcomponentcomeout at different ends,thereare only four waysof wiring the circuit.You can do it by trial and error until the LED lightsand turnsoff whensomethingis put betweenthe two sides of the opto-interrupter.Or you canspenda few minutesand comeup with a strategythat simplifiesthe search.For example,to find the IR LED and its polarity,usethe LED and a 3300 resistor.Tiyeachsidewith differentpolaritiesfor the pins and the LED until the LED lights. Onceyou haveidentifiedthe componentsin each sideof the opto-interrupter,recordwhat eachcomponent is,recordwhich wiresbelongto each,cut apartthe

l0-1q

240

IR white/black circuit

opto-interrupter,andthen placethe opto-interupter in a breadboard(seeFigure10-15).This orientation will allow you to run a pieceof paperwith white and black marksover the IR LED and phototransistor. With this done,addthe three-batterypower supply,the resistors,and the transistor(seeFigure10-14).Thetwo 10k resistorsand the 2N3904NPN transistorwill producean analogvoltagethat can be very easilysensed by the PIC MCU'S comparators. I decidedto usecomparatorsinsteadof the PIC16F684's ADC becauseI didn't expectthere to be a needfor processinganalogvalues(white/black shouldbe very binary),and the comparatoroutputs can be polled continuously, whereasthe ADC mustbe initializedand then polled until the operationis complete.As canbe seenin the applicationcode,the task ol polling the comparatorand turning on the LED (if somethingis reflectinglight from the IR LED to the IR phototransistor)is extremelysimple. Usingyour DMM, measurethe voltagedifference with somethingwhite in front of the lR LED/IR phototransistorpair and then with somethingblack.I used a white sheetof paperthat had largeblack areas printed on it. For testingthe opto-interrupter,I used with the componentsspecified,the voltageat the 2N3904was3.06volts with the black printed paperin hont of the phototransistorand 0.20volts for plain white paper.For the comparator'sVRef module,I choose1/21hese extremes or 1.5volts. To calculatethe valuepassedto the VRef module,I measuredvoltageat the PIC MCU's power pins (asthe VRef module'soutput is proportionalto Vdd) and found it to be 4.54volts.For the VRef module.I decidedto run it in low-rangemode,which allowsfor

Figure l0-'f5 IR surfacesensorcircuit usinga cutapart U-shapedIR opto-isolqtor

l , e 3 P I C @I ' l C UE x o e r i m e n t s f o r

the Evil

Genius

HI X rd

i

t r

lryke Preilko 05.01.03

LISf R=DEC INCrirDE "plSf

I

584. tncn

(D

-CONFIG _ECUEN_OFF & _IESO_OFF & _BOD_OFF & CPD_OEq & _CP_OFE & _!{CLRE_OFF & _P!iIRTE_ON & & _INToscIo _lfttt_orF

t::o, .

:L-

t

l

f".|,

:t

Veliables CBI.oCK 0x020 ENDC

o

b't

-T: r

I'

PAOE Ueinlin€

r+

-L

nop

Figute lo-f6

ry

IR phototrenststorcircuit

voltagesup to two-thirds of Vdd with a fraction denominator of 24.With this information, I calculated the VRef module's voltage specification value to be: Value = (1.5 volts

/ 4.54 volts)

X 24

As you can seein the software for this application (asmRwb.asm),Iput in a valueof 8 (b'1000')to the VRCON register: "aBnIRwb - Us6 Com9arators tille geDaola" whits/BI.ck

with

clrf movlw

PORrA b,00001010,

movwf

CIICONO

baf, cIrf, movln

STATUS, RPo ANSEL ^ 0xg0 b.10101000,

mofidf movhr novrdf bcf

VRCON ^ 0x80 0!a0r TRISA ^ 0x80 STATUS, RPo

IJooP: movlld blfsc

0 C!{CO!{o, CIOU!

lrovLw lrovDrf

1 << { PORIIA

goto

IJoqp

Eo!

\o

ICD Debug

O lrith t Corqtarato! lilodu1e t Vref

I

I 1.5 r Specify ; Tfansilion ; RC{/RCs

H

volt

l'.{

OutDulB

n

with LED of,f t start t if, Cl.viD+ > i Refarenc€ lben lurn on IJED t

IR

This PrograD PolLs th€ voltage cooiag flom IR LED/PbototralEigtor !!dl turrrB on an LED lrh€a th€ voltag€ ia is greaE€r than 1 VoIl. tfh€ coq)arator La ua€dl for tsbl,a op€raELon, Ea!dfirere Noleat PIC15r58{ runriDg at 4 ! lz U5lng th6 Interagl clock 4.{5-{.5 Volt Pow€r (3:. nAA' Cells} RAo - Phototrrnaialor Output RA4l - IJED Anodl€ RA5 - r,ED calhodo

,

a end

The asmRwb.asmcode could be easily extendedto up to four IR phototransistor modules by selectingdifferent comparator inputs (two for eachof the two comparatorsgiving you a total of four). Although if you do this,I recommendyou do your bestto make sure the opto-interrupters have the samepart number so you do not have to charactedzethe circuit repeatedly and provide different comparator (or component) valuesfor eachinout.

S e c t i o nT e n S e n s o r s

24L

rt l-h

0l

o o w o u

o

Ft

()

ExFeriment 91-lnterfacingto Sharp6Paila0

c{

Flanging0biect Sensors N

tu

t3

1 PIC16F68 4 1 Shalp GP2D120 IR !anging moduLe

l*l

1 1o-LED bargraph

fi

I

tu

di.splay

0. 01 pF capacitor

1 Breadboard-mountable SPDT €witch Thlee-cell clip

Dldll Needle-nose pliers liire

*-r

AA battery

AA battelies

stlippers

B!eadboard Wiring

kit

tTr l-r ,r{ d{

(u H

Sharp has a number of different IR object detection and ranging modules that you can interface very simply to any PIC MCU. In this experiment, I will introduceyou to the GP2D120module,which providesan analogsignalroughlyproportionalto the distance betweenit and somelight-reflectingobject.TheSharp modulesare designedto work usingbetween3 and 6 volts,with 4.5to 5.4volts beingthe rangewherethey work mostefficiently.Other than providingreasonably cleanpower to the modules,you haveto connectonly a singleline to a PIC MCU to read distances. The circuit that I usedfor this experiment is quite simple,asyou will seein Figures10-17and 10-18,andit

shouldnot causeyou too many problemsin wiring it together.The basicGP2D120module hasa white plastic connectoron the bottom,and to useit with a bread board,I simplysolderedthreeshort breadboardwiring kit wiresto the threepins on the backsideof the module (seeFigure10-18). The codefor the applicationis very straightforward and assumesthat the maximum voltageput out by the GPZD120is 3.0 volts.Insteadof displayingthe distanceas a binary value,I use the bargraphas a 10position scalewith a singlelit LED. The application code (asmGP2D12)teststhe voltage output from the GPZD120by repeatedlysubtracting15 from the

a

r-6 L)1

-:-:_-r_, I '

t

I I ___-L

a+ 'f Figure 017

242

GP2D12circuit

Figure l0l8 Prototypecircuit seenfrom the rear of the GP2D120module

l , E 3 P I C @l l C U E x p e r i n e n t s f o r

the Evil

Genius

returnedADC value.The reasonfor taking away 15 is that 3.0 volts measuredin a maxirnum255range for a 5-volt circuit is 150.Therefore.15 is eauivalent to 300mV. I havebeenquite cavalierwith the GP2D120in this circuit becausethe circuit has only one LED active at any time and is poweredby batteries,and the breadboard hasa lot of built-in capacitance. If you wereto usethe GP2D120(or any of the other SharpIR object-detectionmodules)in an application,Iwould

recommendplacinga fairly large(10 pF or greater) capacitorcloseto the module'spower-supplypins.As I will showin the following experiments,IRreceivers canbe somewhatsensitiveto electricalnoise,and in an applicationthat haselectricalmotorsrunning (e.g.,a robot),you will find that the output may be erratic.By addingthe capacitor,you shouldbe protectingthe modulefrom noise,which couldpreventit from operatins correctlv,

?:t v1 i-

':'" ..-:.

1.":

Experiment 9?-Do-lt-YourselflH ObjectSensor ti1j I t P1c16E' 684 38 KHz IR TV remote receiver control

1 -:i

1 IR I.ED 1 LED L l0k I

lk

t-x

!esisto! resistor

1 470O !es isto! 1 100O !es isto! DMM

1 lk Breadboald-mouotable potentiomete!

Needle-nose pliers

1 0 .01 pF capacito!

Breadboa!d Breadboald

wiring

1 47 pF electrolyt caPacj.!ol.

kit

i?

ic

i.t

1 Sntn btack heat-shrink 1 to 1.25 inches tubilg (2.5 to 3 cm) in length

f':' ti

1 Breadboa!d-mountable

When Ben Wirz and I designedthe "TAB Electronics Build Your Own Robot Kit," we spentabouta month strugglingwith coming up with a way that objects couldbe detectedusingsimplewiresthat,when moved,would closeor opencircuits.An enormous amountof work wasdone to comeup with a design that wassensitive(would detectan objectwith enough time for the robot to stop),robust(requiredno bending of wiresbackinto shapeafter a collision),reliable (madeno "false"hits),andinexpensive. The solution that we cameup with wasa noncontactmethodof detectingobjectsby usinga modulatedIR light beam and a TV remote-controlreceiver.You would probably be surprisedto discoverthat this methodoutperformedmechanicalswitchesin eachareaoreviouslv

5P51

StdLCCn

1 Three-cel,1 clip

AA battely

ii{

3 AA battelies

,:;

listedin this book and it wascheaperto implement.In this and the experimentsthat follow,I will presentyou with somenoncontactobject-detectionmethodologies with which you can erperiment. When you usea remotecontrol to turn a TV on or off or changethe stationor the volume,the remote controlin your handis usuallysendingout a modulatedstreamof IR light pulses.You may have

S e c t i o nT e n S e n s o r s

243

L.{ i-) !:!a itt

*1 ! f

I

et .Y'a

3.3.i1

.r*s >a L,-{

!

fq

discoveredthat the remotecontrol can"bounce"its output signaloff differentobjectsin the room (e.g.,the wall behindyou) and the TV will respondasif you werepointingthe remotecontrol directly at it. This is the theorybehindthis experiment;asyou canseein Figure10-19,lightis bouncedfrorn an IR LED to aTV remotecontrol via someother obiect.Earlier in this section,an IR white/blacksensorperformeda similar function,but the distanceat which it works is limited to a half-inch(1 cm) or so.The circuit presentedhere can detectobjectsasfar asseveralfeet awayand will evengive you someidea of its distance,asyou will see in the next experiment. Consideringit costsjust a few cents,the TV remotecontrolreceivers(suchasthe SharpGP1UD series) are amazinglycomplex devices.They continually monitor the incomingIR light andrespondto a signalthat is modulated(turned on and off) at 38 kHz. Insidethe TV remote-controlreceiver,the input signalis processed, the and if a 38 kHz signalis encountered, open collector output is pulled low, which allows multiple receiverson the samecircuit. Amazingly it will filter out any constantsignalsand continuallyadaptto its environment.What I discoveredwith the TAB Electronicsrobot is important:It will learnto filter out any continuous38 kHz signalasnoiseif it is left activefor more than a few millisecondsThis is why in Figure1019,I havedrawn a PWM signalthat allowsthe 38 kHz signalto be passedto the IR LED only periodically. Figure10-20showsthe signalsentto an IR LED and the responsefrom a TV remote-controlreceiver;the in the output is delayof severalhundredmicroseconds simplytheTV remote-controlreceiverrecognizingthe incomingsignaland then recognizingthe signalhas stopped. To demonstrateusing an IR LED and TV remotecontrol receiverfor objectdetection,Icameup with the circuit shownin Figure10-21.It'swired with the IR LED bent over and pointingin the samedirectionas the TV remote-controlreceiver(seeFigure10-22).The

IR LED hasa f-inch (2.5cm) pieceof black heatshrink tubing placed over it to direct the IR waveform away frorn the TV remote control. The circuitry shown in Figure10-22is actuallythe circuihy for the next experirnent.The four LEDS are usedto determine the rangefrom the circuitto anotherobject.Only one LED is required for this application. The 1k resistorandpotentiometerusedin the applicationis to limit the amountof currentbeingpassedto the IR LED and thereforeto limit the light output from the LED which will help set the point where objectswill be detected.Thisschemeis often usedin robotsto limit the detectionto 1 foot (30 cm) or so, eventhoughit is not really a recommendedmethodto A better way will be limit the detectiondistance. shownin the next experiment. The first application for testing this circuit is asmlR.asmand simplydelaysfor 50 ms the sendingof 10pulsesto the IR LED. As the signalis beingsent, the TV remote-controloutput is beingpolled,and if the signal is active for two cycles,then the application acknowledges an objectis in front of the circuit. tits1e

"asmlR

Your

own IR

Obj€ct

Thi6 Progr€m Outpul6 a 38 KHz Sigrnal (25 |rs Periotl) aigual a for 10 Cyclea anaMonilolE IR Tv Rdlole Contsrol Receiv€! for reflectionE.

r t t ; r i

Haltlware Notea: PIC15F68{ running at { MHz using the Inlernal Clock Input RC{ - IR R€ceLve! Rco - rnaicator rJED RC5 - IR IJED OulDuts

t i

Myk€

Pretlko

[nnnlnnnt ltltL|il1i1;*__ -IR LED

! 1

a lR LED

0.5%OutyCycle PWMRunninsal20 kHz

OpaqueBarrier

,rd { r

Contrcl Signal 10k?

te{ !c.c

RoIl

i r , ; r

m irt

-

#

ig

**:*:T

5

Reflected SignalReception

€

p u H lJ.oDelctll

Figure l0-19

244

IR detectortheory

i*

5 v

Figufe l0-40

l , P 3 P I C o l l C U E x o e ri m e n t s f o r

100.tr9

IR operation

the Evi I

6enius

Iroop: novlw novwf movLw atltllw blfac flecfaz goto

Fisure l0-al

clrf

IR detectcircuit

HIGH ((50000 / 5) + 256, Dlay Low ((50000 / 5l I 256) -1 tbe ; Wait to Repeat , Test STATUS, Z Dlay, f S-3 ; 5 C-ycle Deley I.ooD i for 20 ma l 20

movrdf IRLoop: goro goto btfaa

PORTC, 4

.T; l l

xo!!rf

Figure 10-22 Breadboardcircuit usedto detect objectsand measurethe distanceto them ,

05.01.03 IJISI R=DEC I N C L TD B n p 1 6 f 6 8 4 . i a c n

1 < < 5 PORTShaalolr, PORTShailow PORTC

fl€cfaz goto

IRIJooIt

novlw aubwf

4 j,

novf aEallw btfsc lorhr lrovwf novwf

PoRTghatlow, or
t r r t t r i , i

nJ. coutrta lh€ Active IR Sead 10 cr,clea. c:tcl€ at a t:ine OutsDuts 8 qlclea Count Lotlr Iilt Delay Fu].l 13 C?clea in IlooD

i i i i

Poll IR R€c6iv€ If, Rea€t, Increlrents Counler roggle RC5

,

org

0

aqD cLrf cllf movlw

t

Coqrarators

TRISC ^ 0x80, STATI'9. RPO PoRlsbailow

0 5

right r Vj.6ibte , OulDuts , IR IJED Oulgut

, CL€a! , Out9ut

r,ED

lh€ PORTC Valu€

\o N I

I

U

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F

o v

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o n

r+

a

o

3

a

o

r-J

Obj€ct

llhia Progrem Oulputs a 38 KHz Siqlal (26 Ea 9erioal) .ignal for 16 CalcIeE uEing the ECCP Ptt!{ a!41 Monitora a IR fV Remole Codtrol Recel,v€r for refleclions. Ealalwale !{otes3 PIC16E584 rurr.oing al 4 llHz Using the Internal Clock RC{ - IR Receiver Input RCo - htlicator LED

S e c t i o nT e n S e n s o r s

o

H

w

I'aEnIR tille Detectorn

C!{CONo STATUS, RPO INSEI. ^ 0x80 TRrAC ^ 0x80,

clrf

ICD Debug

PORIA PORTC 7 i

novtrf

For

3

rF

Although asmlR.asmworks perfectly,Iwantedto come up with a way of performing the sameoperation using the CCP's PWM c cuitry. Instead of having to come up with the 38 kIIz signal for the IR LED in software,the PWM can do it and tell me when it is complete by using the TMMIF flag and the 16-times postscaler.This has some advantagesthat will become apparent presently.The changedapplication is called asmlR 2.asm.

uainlirre

l-r.

anfl

€nd

vari€lc1€s CBLOCK 0x020 i, j DIay PORTShadlolt ENDC

Ff

X

& _BOD_OFF & _colltr'lo _ECME![_oFF & _IESO_OrF _CPD_OAF & _CP_OFF & _!'ICLRE_O!F & _plfR!!E_ON & _}IDT,OFF & _INTOSCIO t

(D

A/2

w

t LooD

rrl X ,rd

245

RC5 -

15

Rua 1'MR2 for cycLes

b,01111100'

IR LED Outpu!

!!2CON $yk€ Prealko 05 . 01. 03 LIST B=DEC rNcrJr[rE rp16f 684. incn -CONFIG _FCIIEN OFF & _IESO_OFF & _BOD_OEF & _CPD_OFF & _CP OEF & -!,!CLRE_OF!' & _PVIRTE_ON & _WDT_OFF & _INTOSCIO

*"4

t

Variabl€s CBI,oCK 0x020

DLay PORTShadlow ENDC

ni

v*

t

STATUS, RPO TRISC ^ 0x80, STATUS, RPO

cl!f

i

IRIJOOP

b!fsB

PORTC,4

incf btf,Ba

PIR1,

bBf bsf

0 nrovwf r For

:--

,'.-Jl

rlovlrtr

rci,tt !

PORTC 7 cltcoN0

b'00001100'

mowf movl$r

ccPlcoll 13

Enable ECCP

P!0tiI Modle of

CCPR].L

b..:i

RPo sTAllrgs, ANSEL ^ 0x80

mov\tf bcf

PR2 ^ 0x80 TRISC ^ 0x80,

bcf

STATUS, RPO PORTShaalow

0

i visible r Output

r,ight

r,ED

clea! lhe PoRTc OulDuts Value

Repeat tbe

i T€EE

i; i:.j

s

STATUS, D1ay, f

cLrf bcf

TMR2 PIRI,

t:1

Z 5 Cyc].e DeLay for 20 ns

TIIR2IF

fo! out

IRlooD STAITUS, RPO TRISC ^ 0x80. S|!ATUS, RPo

5

i

IR tED Output

r Tllrn

b,01111000' T2CON

off

TMR2 Off

30

movf anatlw btfac iorLw

PORTShatlow, o:tFF ^ 1

goto

IJooD

ahilty Carry

PolLs if

Low? Four

Sel

rs TUIN

ON LED?

sraTus, c 1 PORTShaalow POBTC

Carry

Set,

j >= {

CI€ar EMR2 Reaet Inte:arup! Requeat Flagl

Loop

By usingthe PIC MCU's built-in PWM, I have come up with a method of performing this task that doesnot needcountedassemblylanguagestatements to createthe 26ps-periodwavesentto the IR LED. Becausetheseassemblylanguagestatementsare not required,the applicationcould be written in C (as dernonstrated in cIR.c). In cIR.c,you may havenoticedthat I checkthe poll count for only a valueof 15 insteadof 30,asin the asmlR 2.asmroutine. The reason for this wasmy useof the 16-bitvariablei asthe counterinsteadof an eightbit variable.I assumedthat the codewould take approximately twice as long to executewith a 16-bit counter as it would with an eight-bit counter.The asthe codeworks assumptionmustbe reasonable, without anv issues.

.ft ** *1

X i *--1i

246

TUR2 to

end

Hrcn ( (50000 / 5) + 2 5 6 ) Dlay I , o v r ( ( 5 0 0 0 0 / 5 ) + 256, -t r Waits to

btf,ac flecfEz goco

Wai! Time

, get I'uR2 Perioal

IrooD:

adatlw

ON

"j" eount8 the Active IR 8 cycle6 antl Output Count IJow Rx Don,t. If RC4 Eigh, Irlc!€dr€nt coudt

TIIR2IE

lrovlw aub$f

get th€ Pvt!! output Reael Conlrol

baf clrf

I,ED OulpuI

ICD Detrg

Turn off Cof,E)arators

movlrd

IR

!

go!o

PAGE Mairline org

bsf bcf bcf

l , e 3 P I C @l l C U E x p e r i m e n t s f o r

the EviI

6enius

t{ tt

ExFeriment 93-lH Obiect-Flanging Sensor

tn

ils

tv

t1 Fr.

P r c 1 6 F 5 84

H {D x

38 KHz IR TV remote!eceive! control 1 lR LED 4 LEDS I0k

resi sto!

1k res istor 4? of,) resistors

(A)

100O !es isto! 0. 01 pF capacitor

DMM Needle-oose

CapaCl't,Ol

Breadboa!d Breadboard

wiring

!,

4? /rF electrolytic

pliers

H

Smn bLack heat-shrink tubing I to 1.25 inches (2.5 to 3 cm) in length

kit

w o tf

1 Breadboatd-mountable SPST snitch I

Thlee-cell c1ip

AA battely

LJ,

3 AA batteries

In the previousexperiment,I useda 1k potentiometer to limit the amount of curent that passedthe IR LED. By limiting the current,I dimmedthe LED's output and shortenedthe detectiondistance. The problem with this methodis that it is not very reliableand would be difficult to reproduce in a manufacturing setting.If you look at aTV remote-confol receiver's datasheet, you would discoverthat asthe IR LED's modulatingfrequencychangeqso doesthe sensitivity of the TV remote-controlreceiver.If you assumethat a brighter signal is required for the TV remote-control receiver to recognizeit (when the signal was different than 38 kHz), then you would alsoassumethat a closer objectwould producea brighterreflectedsignaland would only be detectedat a closer distance.The purposeof this experiment is to test this hypothesis. To indicatethe basicdistanceto an object,I modified the circuitry from the previous experiment (see Figure10-23).Theactualdifferencesare minor;the 1k potentiometerhasbeenremovedand three additional visible light LEDs and three 470O currenflimiting resistorshavebeenadded.TheseadditionalLEDs are usedto indicatewhetheran objectis detectedat different modulatinsfrequencies.

o

t! The basefor this experiment's code (asmlRDist.asm)wastakenfrom asmlR 2.asm.One of the reasonsfor using the PWM to generatethe modulating IR signalis that it allowschangesto the values passedto it conditionally.By taking the delayand IR objectdetectcodeof the previousexperimentand placingit in a macro,I wasableto comeup with a code

ff

F

11! !"t (A'{

dJ,

r{

'R LEO Sending38 Kh2 -

\\\

tlt

l|l

,/,/l

///

q

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D

4

Lighl

m

l/R 38 Khz

t{ Figure l0-?3

5 e c t i o nT e n S e n s o n s

IR rangingcircuit

247

novhr novlrf bcf

pelioal Plt2 ^ 0x80 gTATuS, RPo

t

S€l

clrf bcf

1'![R2 PIR1,

nrovlw

b,01111100,

I'MR2 Clear Reget Int€lru9t Requeal FIag Run 1l{R2 f,or 15 cycl€a

fhiE Program outputE a drltl-perLotl (atarling at 38 kxz sigmal, 26 lra Perlotl antl golng to a 31 llEz signal, 32 Ea P6!Lot[) aLgaal fo! 16 cyclea uging tsh€ EccP Ptgll aad l{onitsors a IR w R€trole Control R€ce:iver for reflecliong. D€penallng on whLch gig|ral Proaluced a reflectioa, e gpecific LED !ri1L be lit.

t i i r r

novwf

T2CoN

bsf bcf bcf

STAIIUS, RPo TRISC ^ 0x80, SIIATUS, R"0

t

IR

cIrf,

i

btfsE

PORTC, {

![he aclual frequeacy, Pelc€nt off Pelc€Dtag€ andl Rec€Dliv€ ia lidted in the ltaclo invocalionB

ndBinal

blfaa

PIRI,

lilacroa ar€ Nola! this apDlicabion

ir1

basethat could test different modulating frequencies easily aswell as ouFut object detectionsat thesefrequencieson different LEDs.

${

o

"aBnIRDist tille IR Objecl Detectori

n c o

a

Ut g .F{

ttt

c

-

lteasure

ua€tl

Distance

ext€nsively

with

bhe

goto

Eeralware Not€s: PIC15F58{ ruDniDg at { MHz Uaing the Int€rnal Clock - IR R€ceiver RC{ Input RC3:RCo - Inilicato! LEDa - rR r.ED Output RCs

d

€,

I

fl{R2IF

{J

5

uyk€ Preatko 05.01.07

.a

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VariableB CBIOCK 0x020

,

Dlay PORTShatio!. E}IDC

11{R2IF

t Wail t fime

STATUS, RPo TRISC ^ 0x80, gTATug, RPo

movLv nrovwf

b'01111000' T2CON

r Turtt

nov].w auM

30 i, !t

r Thirty t carry

mov! a'1tllrr btf,sc iorlw

PORTShatlorr, w oxFF ^ (1 << ledl) STATUS, C (1 << l€d)

i

5

r IR

IRT€st Macro Deriot!, novlrp b'00001100'

the

IJooD

lrovwf, movhr movlrf

CCP1CON / Doriodl CCPRI!

X

baf,

SIATI,S,

l€d , EDabIe r ECCP 2

t

Square

LED Out9uts Off

I'llR2

Po11s S€l if

cleer

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IrED Bit

t Carrtz Set, j >- 30 i so Turn on I,ED

PAGE Maialine 0 t

clrf novl\r

PORTC 7

movrdf

C!'CONo

bsf clrf movllr

STAIUS, RFo ANSEL ^ 0x80 0x30

novwf,

ERISC

bcf

SfATUg,

PWM !{oil€

clrf

PORTSbatlow

^ 0x80

Eor

ICD Det{rg

Wave Oulput

i Botston { PORTC i Bitss are rJight TJED r visible t OutDuls

RPo

of IJooD 3 Dley5 ons rRT€ats 25,

0

RPo

r Clear the PORTC t outpu! value r 38.{6 kHz ,1-.2%/LoO% r P€rioal = 25 ua, r LEDo

kl

248

Off

t CdE aralors

eudrtr

c,

9{

Delay r 5 Cycl€ 20 n6 i fo!

!t'MR2 lo

PORTShadort PORTC

nop

btfac STATttg, z alecfsz Dlay, f qoto $-3

f,or Out

bsf bsf bcf

org

Macloa i DLay50na !{acro t 50 ns D€Iay novLw HrGH ((50000 / 5, + 256\ novwf DIay novlw LOIq ((50000 / 5l + 255. -1 aatdLw r Wait to R€Dea! t Teat

ON

$-3

movwf tnovwf endm

-CO}IFIG _ECMEN_OFF & _IESO_OFF & _BOD_OFF & _CPD_OFF & _CP_OFF & _MCIJRE_OFF & _PV{RTE_ON & _!{DT_OFF & _r!|TOSCTO

IJED OutDut

countE th€ i "i" IR i Active Don,l i If Rc4 High, Coun! t fncrernent

t l

c,

tt'MR2 Peliod

l , e 3 P I C @l l C U E x o e r i m e n t s f o n t h e E v i l

6enius

DlaysomE 6.O%/9O"/" = 28 r Periotl IJED].

rBTes! 28, D1ay5o:lE rBTest

30,

L2.2%/ 60e" = 30 r Periotl T,ED2

2

t 3L.25 k'lz 20.o%/35e" = 32 i P€rioil LED3

DLay5oms IREest

32,

After building the circuit, I tried it with both Sharp and Liteon IR receivers.I wassurprisedat the nonlinear distancesthe differentfrequenciesproducedfor both manufacturers'products.With a fasterPWM base frequency(i.e.,the PIC MCU's clockfrequency),modelingof the applicationcould take place,and a better understandingof the distancedetectionversusPWM frequencycouldbe developed.

3

i..-j ' q-i

l. .j :-,:, :*

;r:t fti

goro

fi-

€nil r.l.,1

:'!1

Experiment 9t-l- UltrasonitrDistance-Flange 5ensor

i"t 1PlCt6F584

1..:,,

1 Polaroid 6500 ultfasonic ranger

i,t

r

10-LED balgraph

dispLaY

.{;i

1 10k resistor 1 0.01 /rF capacito! 1 1, 000 pF electrolytic (see text ) capacitor 1 6-voJ.t lantern (see text )

DMM

battely

Needle-nose pliers Breadboard Breadboald

wiriog

kit

Although the IR Light provideda basiclevel of object rangingto a sensor,the bestnoncontactmethodfor measudngthe distanceto an objectis to measurethe flight timeof an ultrasonicsignal.A numberof demonstrationcircuitsare availablethat you could look at, but the Polaroid6500is very commonlyused,asit is fairly availableandvery easyto interfaceto. In this experiment,I will showyou how to add a Polaroid6500 ultrasonicrangerto a PIC MCU and useit to measure distances. The Polaroid6500is a high-energydevice.When it is active,it requires1 ampereof current.This is why I specifieda 6-volt lantem batteryfor this experiment insteadof the traditionalAA batteries.This batterywill provideseveralampsof currentfor a surprisinglylong

period of time.I chosethis batterybecauseit could alsobe usedto power the controllingPIC MCU without a voltageregulator.When the Polaroid6500is active,it createson-boardvoltagesin the neighborhood of 400volts (DC). whichwill giveyou a surprising shock(and I am speakingfrom experience)if you are not careful.Whenyou are workingwith the Polaroid6500,make sureyou nevertouch a metal objectthat couldprovide a currentpath throughyour body,and definitelydo not touch the metal transducer (the circularperforatedmetalpieceseenin Figure1024) when it is in operation. The circuit usedfor this experiment(seeFigure1025) is quite simple,althougha coupleof thingsshould be noted whenyou are layingout your own circuit. First,you'll notice thereis no on/off switchin this application.When I usedthe traditionalEG1903 breadboard-mountable switch(ratedfor 200mA, not the 1 amp of this application),Ifound therewasa

S e c t i o nT e n S e n s o r s

249

:f; i a i1,:1 :l-i ! f'\

fri

nr,! ,f.i; ,.1i t a

it i'''l ,|?.

tt

r,nnu, "*f ",nn" f:

i;

i

jr :

"rrn"otitisnr' BetweenInit and.--.--1 . Echo(5.4ms)

r,f:

r!1 Ut

b

3 t

Figure f0-e5

Uhra circuit

I I

LJI

:*-i

significant voltage drop through it and the breadboard tracesthat the power passedthrough.I put the Vdd wire directlyinto the Vcc rail and kept the powerpin of the Polaroid6500very closeto it. In additionto the lack of a switchand the needto keeppowerresistancesto a minimum,thereis a 1,000pF capacitor acrossthe application's Vdd and Vss.The purpose of this largecapacitoris to preventany largedrawsfrom

i

"Echo" Response

lr: +

ait

Figure fO-eq Polnroid 6500ultrasonicranging module with circular transducerdisk (from which rlistancesare measured)along with the breadboard experimentcircuirand 6-volt lanternbattery

I

Figure lO-aE

Uhra waveform

the Polaroid 6500from affecting any of the other circuitry (i.e.,the PIC MCU) in the application. Although wiring the Polaroid 6500into a circuit presentssomeunique challenges,interfacing it to a PIC MCU is very easy.As shown in Figure 10-26,the Init pin (pin 4) is driven high, and then the time required for the ultrasonic signal to be sent from and return to the transduceris the time it takesfor the Echo pin (pin 7) to becomeactive. Assuming that sound travels at 1,127feet per second,it takes73.94/rs to travel 1 inch.When deterrniningtbe time of flighl, you have to assumethat the signal actually takes 147.88pcsfor eachinch, to account for the time out and the time back. In the application code (asmUltra.asm),I rounded up the tirne of flight to 148ps per inch to measurethe time it takes from when the Init pin becomesactive to when the Echo pin acknowledgesthe signal. In asmUltra.asm, whenyou look at the LED bargraph, remember that the fust LED indicates the distance from the transduceris between 0 and 1 foot. The secondLED indicates1 foot and 2 feet,and so on. If the distanceis greater than 10 feet (or an echo is not returned),the first and last LEDs are turned on to indicate the error condition.

: .

250

l , P 3 P I C @l l C U E x p e r i m e n t s f o r

the EviI

Genius

Experiment95-Hobot lFlTag

1Prc16F684 2 38 KHz lR TV lemotecontrol receivers ]. ]R LED High-intensitY LEDs 1 Yellow/Red I

4.7k resistor

4? OF electlolytic capaeitors

DUM wiring

LED

2 100O lesistors

BS2-based robot

Breadboald

white

kit

I don't go out of my way to watchthem,but anytime "Robot Wars,""Battle Bots."or other robot combat showsare on, I love to tape them.It's a lot of fun watchingtwo robotsduke it out with partsflying everywhere,althoughI shudderat the amountof work that is beingdestroyedin just a few minutes.I would love to take part in the competitions,but I would like somebodyelseto rebuild (and pay for) the robots.In this experiment,you can havemany of the thrills of robot fighting,without the mesEcost,and effort of rebuilding.Thisexperimentwill let two, or more, robotsshootat eachother with beamsof lisht and recordthe numberof "hits." The circuit and softwarepresentedherewere originally designedfor the "Thb ElectronicsSumo-Bot Kit," which I codeveloped, but they could be transferred directlyto any other microcontroller-based robot fairly easily.In the photographof the circuit mountedon a Surno-Bot(seeFigure10-27),you can seethe IR LED cannon,enclosedin a pieceof 5mm heafshrink tubing,alongwith the IR receiversand four indicatorLEDs.The operationof the circuit is quite simple,by pressingthe one-barbutton on the robot'sremotecontrol,a speciallycodedsignalis sent from the IR LED cannonto anythingin lront of the robot (e.g.,anotherrobot). If the robot receivesa hit from anotherrobot (the operationof the application preventsa robot from hitting itself),it registersthe hit

Length of 5rnm black 1 heat-shrink tubing, to 1.25 inches (2.5 to 3 cm) Iong

and incrementsa counter.This countercan be set for one,five,or an unlimited numberhits until the indicator LEDs flash,letting the world know that the robot hasbeen"killed." Normally,threehigh-intensitywhite LEDs flashin sequence to allowlight-seeking. autonomousrobotsto find and shootat a human-controlled robot.When a robot hasbeenhit five times.the countercan be resetfrom the BS2,

Figure l0-a7 Fronl view ofTAB ElectronicsSumoBot showingoff itsIR LED "cannon,"receivers, LEDs, and controllingPICl6F684

5 e c t i o nT e n S e n s o r s

25L

With the robot controllingthe motorsand providing basicguidance,the circuit in Figure10-28takes careof the businessof shootingandregisteringhits. If you havea Sumo-Botor a ParallaxBoe-Bot,you might think the circuit will be difficult to wire on the smallbreadboardsthat comewith the robots,but this is really not the case(seeFigure10-29). Thereare a few thingsyou shouldbe awareof when you are assemblingthe circuit: .

The bright white LEDs shouldbe arranged120 degreesapart.This is important to allow autonomousrobots a chanceto "see" their competition and know when to fire on them. The IR LED must havea pieceof 5mm heatshrink tubing placedover it. If the heat-shrink tubing is not in place,the robot'scannonwill havea much wider than 5{o-10-degreefield of fire and be ableto hit its competitorsvery easily.

.

i

,

.

.

The IR receivers'leadsshouldnot be trimmed so they stick up high abovethe robot. As I have outlined the circuit layout,they shouldbe placedroughly back to back to ensurethey receivesignalsfrom all around them. Before startinga tournament,I highly recommend that the two robots are placedfacing eachother,and that one shootsat the other until the other startsflashing.Thenreversethe process. This is lessto ensurethat the receivers are in placethan to make sure the cannonsare properlyaimed.Becausethe cannonsare going into breadboards,they can be easilydislodged and put back into the breadboardsincorrectly. Before the competitionstarts,everybody shouldbe confidentthat his or her robots can fire.This processwill alsoensurethat a competitor hasnot commandedthe PIC16F684to turn off receivinghits from the two IR recervers.

'

Ptc16F684

LEO

I

( . , Labels Indicate Robot Power/8s2 Conneclions

Figure l0-28

IR tag circuit

Figure 10-29 IR tag layout on aTab Electronics Sumo-BotBreadboard

252

The PIC MCU softwarehasresidedon a PIC16C505, PIC16F630, and PIC16F684.It is quite versatileand easilyported to different devices.I have taken out the conditionalassemblycodefor the lowend (PIC16C505)executionto try and make it asreadableaspossible.(You may think this wasa losing battle.)However,I want to point out that the condi tional assemblycodewasusedonly for disablingthe comparatorsandADC (whichthe PIC16C505does not have),changingPORTA in the PIC16F630and PIC16F684to PORTB in the PIC16C505,and taking advantageof the TRIS instructionof the PIC16C505. This lastchangewasthe most significantand potentially the most confusingwhenyou read the code;to provide a one-instructionaccessto the TRISA register, I placedits addressin the FSR registerrather than setting and resetting the RPObit of the STATUS register. Table10-2liststhe differentBS2 commandsthat are built into the PIC16F684for controllingthe IR tag circuit.Thesecommandswere chosento give the user asmuch flexibility aspossible.Note that the only BS2 commandthat returnsvaluesis 16,not 0x81that I use in the BS2interfaceapplicationspresentedin this book. I createdthis application(asmlRTag.asm) beforestartingthis book, and I followedthe BS2interfacebuilt into the Sumo-Botrather than thinking of a more genericstandard.Second,noticethat the robot will fire only oncea second,and if the hit-counter valuehasbeenreached,it can no longerfire until it is reset.

l , a 3 P I C @l ' l C l JE x o e ni me n t s f o r

the EviI

Genius

I alsohavelisteda sampleSumo-Botapplication (calledMax 5 Tournament.bs2) for a five-hit toumament competition.Thiscodeis loadedinto the robot's BS2and allowsthe robot to be controlledby the robot'sremotecontrolaswell asfire at its opponent. This circuit (and software)hasbeentestedon a vari ety of differentSumo-Botsand hasbeenbuilt by a fair numberof people.Throughquite a bit of testing,we havefound that the five-hit tournamentseemsto be optimal,givinga minuteand a half of combatand an opportunityfor somebodyto comefrom behindand win.The toumamentsare very excitingand asfun as watchingother people'srobotsdestroyeachother on TV.

Table 10-2 lF B5e Eommandssupported bs the PlEl6F6Br-{ Tag MiErocontroller Eommand

Value Comments

TagFire

1

Fire onceper second.No firing when robot "killed"

TaglROff

2

Turn off the IR sensors

TagIROn

3

Tum on the IR sensors(defaultcondition)

Tagwhiteoff

4

All three white LEDS are turned off

TagwhiteAll

5

All three white LEDS are turned on

Tagleftwhite

6

Togglethe stateof the left white LED

TagRightwhite 7

Togglethe stateof the right white LED

TagRearwhite

Togglethe stateof the rear white LED

8

Tagwhitecycle 9

f€t t

t't yv4

,4 1tJ Fq

L.'l

white LEDS cycle(defaultcondition)

I

Taglndon

10

lndicator LED on

Taglndoff

11

Indicator LED off (defaultcondition)

TagHitclear

12

High counterclear

p

TagMaxHitl

13

Maximum t hit beforeLEDS flash/firing stops

0 FT.

TagMaxHits

14

Maximum 5 hits before LEDS flash/firingstops

TagNoMaxHit

15

No maximumhits (defaultcondition)

TagcetHitNum

16

RETURN the number ofhits in the counler

i

.!. t

$rt

ry rx*

S e c t i o nT e n S e n s o r s

253

Section

Eleven

Motorfontrol PIC12F575 or PICl6F58 4based BS2 cotnnand si-mulator intelface DMM c^1

rarr

n^

t r^n

Solde! Needle-nose pliers Wire clippers Breadboard k j.t

Wiring

S ci s s o r s Krazy Glue I

1 B!eadboard-mountable

P r c 1 5 F 6 84

1 L293D motor

driver

DC motols

chip

2N3904 NPN bipolar

transistors

1 Bipolar

2N3905 PNP bipoLa!

transistors

t

1N914 (1N4148) silicon disp lay

1 Fou!-celI

I

Servo connecto!

(see text )

I

SIP I

Thlee-cell

poten-

Six-pin text)

(see text)

selvos clip

AA battery

clip

batteries

0.100-inch

Four-pin text)

0.01 pF capacitor

motor

A,A battely

AA alkaline

4 10of,) resistors 10k breadboald-mountable t iomet e !

steppe!

Radio control

diodes

10-LED barglaph

resistor

stepper moto!

Unipolar

I

1 470f, 1o-pin

SPST s!ritch

0.10o-inch

header heade!

(see (see

Ca!dboard

I expectthat you feel you understandsmallDC motors very well;you'vebeenexposedto them sinceyou were a smallchild,in toys and differentdevices.You've probablyseenhow you canreversethe directionof motor rotation by switchingthe polarity of the battery that drives.And, you surelyknow that you canchange the speedof the motor by addingmore batteries.It doesn'tseemlike thereis muchmore to understand. As it tums out, there'squite a bit more,especially whenyou considerthat the basisof all typesof motors ts the inductor(or coil).To devisedifferentmethodsof controllingcurrentandpower to the inductor,you needto be awareof the moderateto high currentthat passesthroughit and of the "kickback" produced when the amount of current passingthrough the

inductoris changed.An inductorstoresenergyasa magneticfield.When the currentpassingthroughthe coil is changed,the coil resiststhis change,asit will causea changein the amountof energystoredin the magneticfield. This resistanceto changetakes the form of largevoltagespikesand currenttransients. Figure11-1showsa simpleNPN transistorcontrol of an inductor.The diodebesidethe inductoris a kickback diode,designedto absorbthe voltageand current transientsproducedwhenthe transistorturns on and off.When usinga bipolar transistorfor motor control, this diode must alwaysbe present.This circuit can be usedasthe basisof a DC motor control by changing the inductorwith a relay and then wiring the application. asshownin Fisure 11-2.

255

' "Kickback" supressing diode Figure l'f-l

Coil control

Fiqure fl-?

Relaycontrol

r{

G f''l "tJ

o

U

t4

u

L.i

X , ,

$ P

CI !*{

l![

ti ! t

"rg , t

Eu

The relaymotor-controlctcuit of Figure11-2is the first approachmanypeopleuseto controllinga motor. This is disappointingbecauseit is redundant,especially comparedwith the single-transistormotor control of Figure11-3.Thereare reasonsfor usinga relayin some applications;for example,the available driver transistors cannot switch enough current to effectively power the motor or the voltagedrop throughthe transistoris too high for the motor selectedfor the applicationto work at full power.But for the mostpart,you should be usingthe simplesingle-transistor motor control. Not only doesthe circuit control the basic operation of tuming on and off the motor, it also allows very fast switching of the motor, which in turn allows you to use high-speedpulse wi.dthmodulation (PWM) for motorspeedcontrol, rather than attempting to vary the voltagelevel, which can be very problematic. There is a basicproblem with the motor control shownin Figure11-3:Thedirectionof the motor cannot be reversed.Figure11-4showsapll H-bridgecirczjl in which the direction of current passingthrough the motors can be changedby selectingdifferent

256

Figure lf-3

Motor control

transistors. In this sectionyou will be building a full Hbridgecircuit usingdiscretebipolar transistors,and you will seea common full H-bridge chip that can be usedfor controllingtwo DC motorssimultaneously. A modification to the full bridge is the ftaf Hbridgecircuit(seeFigure11-5).Althoughrequiringliterallytwicethe powersupplyof the full H-bridge,the half H-bridgerequiresonly half the numberof driver transistors.This circuit has advantagesover the full Hbridge,asit doesnot requirecomplementaryPNP or P-ChannelMOSFETSto the NPN or N-Channel MOSFET drivers. In this section,I will experimentwith a numberof different DC motors.their drivers. and PIC$ MCU softwarecontrolmethodologies. I am goingto assume that you understandbasictransistortheory and the operation of PWMs. By doing so we can focus on how the PIC MCU canbe usedto control DC motorsand what kind of built-in featuresare availableto take advantaseol

Flgure lf -f.l Full H-bridse circuit

l , e 3 P f C @H C U E x p e n i m e n t s f o r

the Evil

6enius

I specifiedthe particularpartsfor motor driversin the followingexperimentsbecausethesepartsshould (a) be easyto find, and (b) work with virtually all motors.The parts are not optimizedfor specific motors,and you will find caseswherethe motorswill not developfull torque,will drain your batteries quickly,and/orwill get warm.Thedrivers,motors,and PIC MCUs usedin the experimentsshouldn'tbecome uncomfortablyhot to the touch.The purposeof this sectionis to demonstratehow the PIC MCU is usedto controlmotors.not how to desisnmoior drivers.

rrl &!f

t?*! 1V fj

*-"' i*e :i?

5 ,€,

Figure lf-5

Half H-bridgecircuit :

a

ExFeriment 9E-DE MotorDrivenUsingthe CfP PIIJM and U5inga Potentiometer Control I

Prc16F584 2N3904 NPN bipola! transisto!s

{ 't'

2N3906 PNP bipolar transi sto!s

;}|;

4 1 N 9 1 4 ( 1 N 4 1 4 8) s i l i c o n diodes 4 100f) !es istors

DMM Soldeling

ilon

So Ide! Need1e-nose $fi!e

pliers

kit

Programming a transistor to turn a motor on and off is a very simple application for the PIC MCU I would expectthat at this point,you would be ableto createan applicationthat senta high output to an VO pin that wasconnectedto a current-limitingresistorand a PNP transistor.In this application,I want to jump dght to creatinga fairly complexcontrol applicationthat allowsforwardsand reverses, aswell asspeedcontrol of a DC motor usingthe full H-bridgecircuit (seeFigure 11-6).Thedirectionand speedof the motor is specified by the potentiometer.When the potentiometeris

,:,

1 B!eadboa!d-mountable SPSf switch

4.";

i.'

:a;

(see text)

1 fhlee-cell clip

Breadboa!d Wiling

9,,

1 0.01 FF capacitor

1 DC motor

clippers

!*

1 10k breadboa!d-mountable potentiometer

AA alkaline

AA battely batteries

centered,the motor is stopped.Whenthe potentiometer is turnedtoward one extreme,the motor will start turning and speedup asthe potentiometerreachesthe end of its travel.If the potentiometeris tumed in the oppositedirectionfrom center,the motor will turn in the oppositedfuection,startingoff slowlyand moving much fasterasthe wiper approachesthe other stop. This is a fairly intuitive interface and one that will allow you to seethe operationof the H-bridge aswell asthe PWM signalthat controlsthe motor'sspeed.

Section Eleven l ' l o t o r C o n t r o l

257

R{t i) Itc l

!

RC4

I

l\ l9c

RC2

.'l-

5.0

I _]_ -:_ Figurel1-5 DC motor circuit Thc cilcuit (seeFigurc 11-6)wasdesignedfor using the PWM capabilities oI the PIC16F684's ECCP,which requiresRC-5:RC2to interfaceto lour motor drivers andrun tr singlemotor in both directions with PWM speedcontrol.My prototypecircuitwasbuilt on a snall breaclboardasshownin Figure11-7,and I useda smallhobbymotor ratedat 4 volts,which I boughtat an electronicsstorc.The strandedwire usedto connect powerto thc motorwassolderedto clippedleadsso that they couldbe pluggedin directlyto a breadboard. As I indicatedpreviously, oneof the purposes of thisexperiment is to controlthe motorsusingthe builfin ECCPPWM anda potentiometer, whichis polled oncccvery 100n]s for controllingthe speedand dircctionof the motor.A PWM frequencyof 15 kHz waschosen,asit allowsa 6,t,stepPWM control output andstillrunsabovethe rangeof mostpeople'shearing.Generally,a PWM control output of 20 kHz is desired, asit is abovethe rangcof hearingarrdwill not affcctother devices. To producea PWM of 20 kHz, a TMR2 resetvaluc of 48 would haveto be procluced, whichrequircspassingone third ol the valueof thc ADC, ratherthanone-halfasI havedonein thisappli catron. Thc ECCPPWM is quitceasyto setup but does not alwayswork properlywhenPNP bipolartransistors are used.asin this expcriment.The high outpul of the Plcl6F6ll4is lcssrhanthevdd appliedto rhePNP transistor, andwhenthe PIC MCU outputwashigh (whichturnedoiTthe PNP transistor), somccurrent flow remained.To climinatethis cun'cntflow,aswell as any potentialcurrentflow to the NPN transistorswhen

258

Fiqure1l-7 SingleDC ntotorcontrolcircuitusing discretetrqnsistors they are supposedto be off,I madethe pin connectcd to thebaseof the unusedtransistor an input.l'he application codeis calledasmMotor.asm: trasnMotor title a Prc16F68{n

Ehis

Program

-

Controlling

Monitors

a Pot

a

at

DC Uotor Accoralingly. Values 0x80 rnove the motor in reverse while Values than 0r<80 move the motor forwaltls. I4hen the at an extren€. the ECCP PwM lnoves at f,ul1 speed. Hardvrare Notes: PIC15F584 running at the Inter$al CLock

l , a l P I C r ' l' l C U E x p e r i m e n t s f o n t h e E v i l

DC Mo!o!

tA3 less

(RA3) Ehan

qreater Pot

4 MHz Using

Genius

is

f,lom

t r t r t

IIAA - Pot RCs/PAA RC{/PIB RC3/P1C RC2./PlD -

i r r

l&lk€ Prettko 05.01.09

grolo

Cotlmanal Motor Forwalals High (on Lo$) ltoto! Revelae Pt, uoto! Revelse Hish llotor Forwarala Pwlt (on Low)

$ -

1

f4

movf, movwf, lnovlw

ADRESE, ADcvalue 0x80

w

; Readl the

subwf btf,ss

ADCValu€, w SllATus, c

r IreEE than 0x80 t ia ReverEe

CONFIG FCllElN OEF & IESO OFF & aOD OFF & _CPD_OFF & _CP_OFF & _MCLRE_OFF & .PIIRTE ON & _!|D4!_OFF & _TNEOSCTO

movhr

b'01001110'

novlrf

ccPlcoN

Vari..bl€E CBLOCK 0x020 D].ay ADCVaIU€ EIIDC

bBf bEf

STATUS, RPo TRISC ^ 0x80,

3

b8f

TRrsc

^ 0x90,

{

bcf

TRISC

^ OxgO,

5

bcf

TRISC ^ 0x80,

bcf bcf rif monnf

RPo SllAmS. STATUS, C ADCValue, w ccPRlL

goEo

IJooD

t

,

PAGE Iilainlin€ org

0 t ror

nop clrf llovlw

ICD

D6bug

PORTC 7

2

t colqltalaEorB trovrdf rnovlw novwf clrf

c!{coNo b,00001101' ADCONo T!lR2

novhr

b'00000100'

novwf clrf

T2CON CCPR1L

r Enable

T'![R2 as r u8ing t Gen€ralor

r Nothing r (YeC)

STATug, RPo 1 << 3 INSEL ^ 0x80

r RA{

novlw

b,00010000,

, gelect

lrovlrf novlw

ADCON1 a 0r.80 6l

novwf lrovlw novwf bcf

PR2 ^ 0x80 b'000011' TRISC ^ 0x80 SEATUS, RPo

movlrr

b'01001110'

rrovwf

ccPlco!{

movlw aaLlrw btfsc alecfaz goto bsE blfsc

IIIGH DLay

((100000

llotorR€velae! novllr ox?F

t

r EnabLe r wilh

movhr

b,11001110,

nov\rf

ccPlcoN

f,

baf

STAIUS, RPo

baf

TRISC

baf

TRrsc ^ 0x90, 2

bcf

TRISC

^ 0x90,

3

bcf

TRISC

^ 0x80,

4

bcf bcf rlf novwf

sTATuS, RPo sTATuS, C ADCVaLue, w CCPR1L

goto

IJooP

^ 0r.80,

5

for

P$u Folwalals

5, + 256) r DeLay 100 ng

ADc t start i Wail for it r finish

Divial€ ADvaIue / 2 for PliU Value Eaable Pwu Forwarala with P1.A/ PLC lPAB I PLD Activ€ High

r t r t r t r t

Turn PtrIP Tur[ NPN firr! PNP Purn NPN

r r t t

Have the llew ADC Linit wail 100 ms to ResamDle

off Low Sial€ Driv€r off High siale Driver od lligh Siale Drive! oN Low sitle Dliver

i"*

& ;J f&

l a.\ \l/ r\i. b' I

I

U ?

Off Low sitl€ r rurn t PNP Driver

t rurn

of,f High siile

'

NPN

r t t t

rurn On Eigh sial€ PNP Dliver Turn ON Low SidI€ NPN Driver

D!iVET

i , r t

llave tshe Nelr AlC rJlmit Wait 100 mE to Reaarmple

a Dc Motor

usiag

a

to

S e c t i o nE l e v e n J ' l o t o r C o n t n o l


{e

B.,e

Along with writing the application in assembler,I translated it into C as cMotor.c as follows: *inclual€ - control slroto! /* Potenliodreter

t-{ lJ.

€nal

Dlav, f S - 3 co GO

aDcvalue,

Foac/8

, S€tsW) th€ IJlmlt , the Ptglr r 15 kHz Fraquelcy t RC5:RC2 Outputs

I

aa

t Betn€en ADc Pol!'a low ((100000 I sl + 2s6l _t STATUS,z

aDcoNo, AIrONo,

xorwf

uovj.ng

A.Dc clock

r ; t t ' t

!-t

l..

a PWtl

(A!{3 ) A.DC hput

go

, Che€sy 7 Bit of the i Negation ccPRlIr t R€v€lse , Value i Enab].e Pt{!l Revelae wfth i PIAIPAC/PLB/PTD Hish r Active

r Eaabl€ 5uR2

bsf novLw noverf

IJooD 3 nrovlw lna,vwf

A.DC on RA{

X

b

t Eorwarala or t Revelae?

goto llolorRevera€ lilotolForrrarfls : mov f ADcvatue

LIST R=DEC INCLITDE'rp16f 68{. incrl

ADC Valu€

259

lltia Proglam ltonitorE a pot at lta3 (RA3) and moveE a DC uotor Accotdingly. values less than 0x80 nove the molor in leverse whil€ ValueE gr€ater tlran 0x80 nov6 tb€ motor forrraral6. when th€ Pots is a! ar extreme, the ECCP pwlt novea al full Epeeal.

Hartbrare Notes: PIC16F584 ruaniDg at 4 MEz Using the rntertral Clock RA{ - Pot Cormartl RCs/P1I' - liotor FonralalE High RC4/P1B - lilotor R€v€rae PWM (on IJolr) RC3/!1C - lloto! R€verse Eigh RC2/P1D - liloto! Forrdalals PWU (on Low)

NOpO, (D1aY - 0i DlaY < 5655, for // 100 lls betveen NOP O T // sarE)l€s

Dlay++) t

GODOT{E = 1t // R€adI Pob Valu€ (GODONE)t tdhil€ - ADRESE, // Reaft in ADC Valu€ (A.Dsvalue > 0x80) // go Forwarala

ADCValue if

{ CCPRUJ = (e.DCVaIue - 80) >> 1, C C P 1 C O N= 0 b 0 1 0 0 1 1 1 0 t TRISC = 0b011011, // eC5/*C2 OulDuc, RC3/RC4 Input

n[ake gretlho 05, 01.10

]

g

(u .Fl

i.l

rl

t{

o lJ o

x

U CI I I

€1ae & WD1IDIS & PIIRTEN & IICIJRDIS & -CONI'IG(INEIO I'I{PROIECT \ & IINPROITECT A BORDIS & IESODIS & FCMDIS) t

int

Dlayt

char

// ADCValu€i

nain(

)

I.ED T:ime on D€Lay va?iable

t PORTC = 0t CUCONo - 7, ConDaralors // Turn off ANSEIJ-1<<3t // R}'4 (AN3) is the ADC rryrur A.DCONo = 0b00001101t on th€ aDC // Tuln garll,l€ // BLE 7 - IJefl iruEtl.fi€dl // BLt 5 - Use VDD // aLE 4r2 - R?.4 / I Bi,E L - Do not SEar! / / BIE O - !!urn on A.DC A.DCONI = 0b00010000t // select the clock a3 Fosc/8 TuR2 = 0,

\o o\ lJ l"a

I!'tR2

//

Provlales

pwlt p€rioat

PR2 = 6{, / / L5 Wz pvtlt F!€qu€ncy r2CON = 0b00000100t // Enable TMR2 CCPR1IJ = 0t // O DtiEY C-!'c1€ to start whil€(1

== 1)

Off

(

//

Glo in

Rev€rae

^ 0x7F) CCPR1IJ = (ADcfalue CCPlcoN = 0b11001110, TRISC - 0b100111t RC3/RC4 Input // RC5/RC2 output, | // fi ) // eLihw l // Enal cMotor

>> l.t

You should be aware of a few things before beginning this experiment.First, the circuit is meant to work with a wide variety of different small hobby motors. You may find that the circuit doesnot havea very long battery life, the transistorsget warm due to excessive current passingthrough them, or the motors do not produce a lot of torque.As indicated previously,the motor drivers are general-purposecircuits.Therefore by understandingyour motor's parametersand specified power supply,and by using driver transistors with appropriate current, voltage,and resistanceparameters,your circuits will be more likely to perform at rnaxirnum efficiency.The four kickback suppression diodes are not optional, even if you have a very small motor. And, if your circuit acts strangely,you may wish to add a 10 to 47 pF electrolyic capacitor to the PIC MCU's power pins and a 0.L pF capacitor acrossthe motor to help reduce the electrical noise produced by the motor. Do not disassemblethis circuit when you are finished;it will be requiredfor the next experiment.

o H

.Fl

l{ (,

9{

x

til

260

l , P 3 P I C o I I C U E x p e ri m e n t s f o r

the Evil

Genius

ExFeriment 97-DE MotorControlurith

rr:

S im pleT MH OPI-U M

H tl,

i.+ I

P rcr.6F 58 4

t-n

2N3904 NPN bipolar trans istors 2N3905 PNP bipola! trans istors 1N914 (1N4148) si Iicon diodes DMM

100O resistols

Needle-nose I[ire

q

pLiels

clippels

Breadboard

I

0.01 FF capaci.tor

Wiri,ng

1

B!eadboard-mountable SPSr switch

kit

AA alkaline

The applicationcodefor this experimentis called asmMotor2.asm.Along with the reducedPWM interval,I alsoaddeda very simplestatemachinethat alternativelysetsthe GO/DONE bit of ADCONO and r e a d st h ev a l u ei n A D R E S H .I n t h ep r e v i o uesx p e r i ment,I couldpoll the stateof GO/DONE continuously,asthe PWM operatesin the background without any softwareintervention(other than to disableor

. ! t

AA battery

Thlee-cell clip

The applicationcircuit for this experimentis the sameasin the preyiousexperiment(seethe schematic in Figure11-6and prototypewiring in Figure11-7).

,

(see text )

DC moto!

This experimentis a repeatof the previousone,except insteadof usingthe builfin ECCP PWM circuitry I usedTMR0 to overflowevery1,024cycles,providinga timebasefor the PWM. By delayingfor 32 cycles,a 30 Hz PWM is produced.Although in the previousexperiment,I usedthe built-in PWM hardwareto producea signalabovethe rangeof humanhearing,by using TMR0 I have created a PWM signal below human hearing.Severalreasonsexistfor doing this.First,small hobbyand toy motorsoften work more efficientlyat very low PWM frequencies. Another reasonis to allow a basictimebasein the softwareso other eventsor elements(includingmultiple motors)canbe synchronized.This is a very important considerationwhenyou are designinga robot.Finally,TMR0-based timebase allowsthe useof low-costPIC MCUs that don't have built-in PWM generators.

I

10k breadboald-mountable potentiomete!

batteries

-.ft

changethe PWM duty cycle).Another differenceis that the pin valuesof RC5:RC2do not change,but to changehow the H-bridgeoperates,Ichangedthe pin bit input/outputmodevaluesin theTRISC register. "asntMotor 2 - Dc uolor tsitle TllRo TLrrebaaetr

conlrol

uaing

a

Thia Plogram !4onitor8 a Pot aE &43 (RA3) valueB anal rroves a DC llotor Accoralingly. leaE lhan 0x80 nrove the rnoto! in !€velEe greater whiLe values tha! 0x80 lrove the rrotor foiwarals. whed the Po! is at an extreme, Pl'iU nove€ at fulL the Sof,tware ape€dl. Halabrale Notea: PrC16F5g{ ruflring al 4 MHz UBing tshe Intelna1 Clock RA{ - Pot Comtrand RC5/P1A - Motor EornaltlE Hish - Molor Reverse PWU (on lrow) RC{/PIB RC3/PLc - uotor Revelse ltigb RC2IP1D - Uolor Forwardls P$U (on low)

Myhe Preflko 0s.01.10 LIST R=DEC rNcrrtDE np15f 584. incn

_coltI'rc -FcttEN-oFF & _rEso_oFr' & _BoD_oFF & CPD OFE & CP OTF & I'ICLRE OFF & .PI{RTE-ON & WDf OTE & INTOSCIO

setrtionEleven l l o t o n C o n t r o l

26L

a"r

( J

e 'J

,*t"

' , J

Variables CBLOCK 0x020 Dilection iDcstate, ADcvalue PV {Duty, Ptfl{Cycle ENDC t

clrf goto

PAGE Uainline olg

bcf 0

r!f

nop

s"*s €

6

r 1

&.; t !

n t

:1 I

d.r

t

For

ICD

Set

PORTC Accoraling

Debug

rrf

novlw

b,010111,

t

trrovwf movLw movwf novLw novwf, clrf

PoRTC 7 cucoNo b'00001101, ADCONo TllRo

Palameter6 t OperaEing ; lPurn off Corq)aratora

bsf novlw no.trwf novlw monwf movlw

t Enable r uging t Base

bcf

IN'IICON, ToIE

clrf clrf clrf

A.DCSlale PwllDuty P$UCycle

clrf

Dileclion

, Wail fo! i Ov€rflov

TURO to

Not Uoving ats First Start at the B€gi ring lloving Eorwalals

INTCON, TOIF

t waits for t Ov€rf1ow

IN:ICON,

t Reset, andl Wait t Next

I ,

F"*

flt

btsfEc goto baf baf golo ADCR€aal: lrovf fiovrof clrf A,DCDone: movlw Eubwf btfas goto

"F{

l'L,

g{

IIOIF

tDcstat€, 0 LDcR€ad ADCONo, cO ADCStat€, 0 aDcDone

0x80 ADgvalue, w STATUS, C

gtalt

or

fo!

i Move

novf

PliEtDuty,

aulnrf movlw blfsc novlw btfEc novlw bsf movwf bcf

P$UCycL€, b,011011, Dilection. b,100111, STATUS, b,111111, STATUS, TRISC ^ STATUS,

incf

PWUCycle,

f

bcf

PWMCycle,

5

goto

Loop

Backwalals

t Check Eo upalatse tbe t Motor t If Duty > CycLe, th€n

w

Reaal the

t OriginaL i Proceaa i

Fofirarala

i

teaa

vt 0

r TRISC Foll'arats t Fot-walals or Revefse? r TRISC Reverse

C r Turn

off

lilotorB?

R.Po 0xg0 RPo tshe Plgtt t Increnent i CycLe Count , M6ximrll of 32 Stat.eg i i

Finiahetl, Again

IJoop Alountl

<9ic.h> *iaclual€ cuot-ot 2 - Control /* Pot€ntsidretet

Statse A.DC Value

than

Reverse?

0x80

go in

Eh€ VaLue r Conv€r! r from 7 BitsE

using

a

Thi6 Proglam llonitols a Pot at RA3 (!rA3) aad moves a DC Motor Accordingly. Values leEs than 0x80 nove the motor in leverse gl6at,e! whil€ valu€6 than 0x80 nov€ the rnotol fonsarals. A 1 ma looD (proaluceit by I'MR0 ) is u8eal to Droviale a 30 Uz PWU for toy nrotors

A.DC Value

ol

a DC Uotor

Harahrate t{otes 3 PIC16F6g{ running at { MBz Ugilrg the Int€rDal clock nA4 - Pot Cdmand RC5/P1A - Motsor Forwatalg Elgh RC{/P1B - MoCor Revera€ P}ru (on Low) RC3/P1C - lilotor Reverae Eigb RC2IP1D - lloto! Forwartls PWI,I (on lJolr)

rryke Drealko 05.01.10

fi

t*i 262

Value

I createda C versionof this applicationcalledcMotor Z.c.

Reaal ADC?

llotorRev€rse

PwltDuly, f, STATUS, C PtCDlDuly, f

!h€ t Convelt ; f rdr 7 Bita ; to5

enal

ADC Readl , Stalt t Ne:{ts State i

A.DRESE, w Alcvalue A.DCState

lfotorForwarale: novwf PWuDuty bcf STATUS, C rrf bcf, rrf

,

, Cheesy 7 Bi! Negatio! , of the CCPR1IJ Value i Revers€

Timer

gfoEo bcf

Plirllurtsy, f STATUS, C PIgUDuty, f 1 Directiou

Uotorlrpdale:

TMRo aa a Plitlt

monwf bcf

r r r i

ADCValue, w PI{!4Duty SltATItS, C

Fonraitlg

AIrc on AA{

STATUS, RPo b,11010001, , 1:{ prescaler to TMITO OPTION_REG ^ 0x80t 1 << 3 r A,A{ (AN3) ADC fnput ANSEL ^ 0x80 b,00010000, i geLect ADC Clock as i Eosc/8 ADCON1 ^ 0x80 STAT['S, RPo

IrooD: btfss

; llov€

!4otolReverae : novlw 0x7F xoriwf

,

Direction Motolupala!€

l , a 3 P I C @l " l C UE x o e n i n e n t s

fon the EviI 6enius

n

) ( INTIO & WIIIIDIS & PWRIIEN & UCI,RDIS & -CONFIG I'NPROTEC! \ & I'IIPROTECI! & BORDIS & IESODIS & FC!,IDIS) '

elae

{ = ADRESET ADCvalu€ = 0t irDcstate // ReBet stale , // fi

A.DCStale = 0t ADcvaluei = 0t Directiott PWuDuty = 0t = 0t Pllllcycl€

char cha! char cbar cba!

n h.t

Read AlC

//

s

uachine

r,"d

(aDcvalue >= 0x80) Coftlanal? // Eorwaral

tf

t PWUDuty = (ADCValu€ - 0t Direction

-

0x80)

s"*

>> 2t

fn

)

nain ( )

t

F.{ // PORTC = 0b010u1t valueg // PORTC to Conlrol CI{CONo = 7, otf ConDalatsors // \Jt]r ANSEIT=1<<3t // RA4 (AlI3 ) is lhe A.Dc Input

Revelse

t P$UDuty = (llDcvalu€ - 1t Dileclion

^ 0x7E)

>> 2t

, // fr

".fl

if, (0 == Dilection) TRISC = 0b011011; // Enable Forwaral €1Be rRISC = 0b100111; // Enable R€vers€

A.DcoNo = 0b00001101t on lhe nDC // firln .tuslifieit // Bi-E 7 - teft Sanpl€ 5 - use vDD // Bit ll BLE 4r2 - rrA4 / / BLE ! - Do not Slarl oa ADc // BiE O - Tuln aDCONI = 0b000X0000t aa Foac/g // selecE the clock

if

t Bits

F

Bite

H

( Pll!,lcyc1e >= Ir9{!'Duty} TRISC = 0b111111t // StsoP !4oto!s PflUcycle

= (Pwt'tcycle

+ al

! { } % 32,

1.uR0 = 0 i // use T!{Ro for oPTIoN = 0b11010001, // 1:4 Proacal€r

a 1 ma D€lay ) to

uae

rnt€rrupts

EIag

for

1 ms

whl.1€ (1 == 1)

t whiLe ( !TOI!) t r!|Ro to overflow // Wait fo! ToIF = 0t // Reaet f,or Nex! 1 lla D€Iay (0 == .aDcstate) or / / sEart

if

R€adI aDc?

t

GODONE= 1t // gtart ADcgtate = 1,

ADc

// elihw Enal cMotor

5,,i;tr 2

T!!Ro

ToIF = 0t //

) //

This code is much easierto follow than the assembly codeversion.But if you look closely,you will discover that the C code specifyingthe on/off of the motor works differently, and even if the PWM has a duty cycle of 0 percent (fully off), the motor driver will be on for a very short time (just a few g,s)before the softwaredeterminesit shouldbe turned off cornpletely.The reasonfor the difference is primarily an oversighton my part. I discoveredit only whenI comparedthe operationof the two programsline by line after seeingthe very shortpulseson my oscilloscope whenI looked at the operationof the two applications.

S e c t i o nE l e v e n l l o t o r C o n t n o l

263

L; ...-: r."1.

:t

n

Experiment 98-ControllingMultipleMotors urith PIIJMand 852 lnterface

[.1

o

i=r

A

I fil

1 L293D moto!

.-f

&

DC motols 1 Fou!-celI clip

F{

DMM

tn

Needle-nose pliers Wire clippers B!eadboard Wiring

F{

kit

,-|

o

U I

@

AA battely

One of the pointsI madein the previousexperiment wasthat multiple motors and complexcontrol softwarecouldbe addedto the 30 Hz motor controlPWM software.This is due to the relatively large number of rycles the code spendswaiting for TMRO to overflow beforeupdatingthe motor PWM code.In this experiment,a secondmotor is addedto the control codethat executeswhile waiting for TMR0 to overflow and that polls for the BS2instrumentinterfacethat wascreated in the previoussection. Insteadof repeatingthe build of the four-transistor H-bridgeusedin the previoustwo experiments,I

decidedto usethe L293D chip,which consistsof four two-outputlevelmotor driversasshownin Figure 11-8.Thechip includeskickbackdiodeson the outputq so you do not haveto add them to your circuit,and is designedfor driving two motors with an extra PWM output control (pins1 and 9).But for most applications,I simplytie theseinputshigh and control the operationof the motor by changingthe level of the control outputs.The chip runs on a 4.5-to 6.0-volt powerinput (Vcc on pin 16) and canswitcha higheror lower voltage i4put on Mot Powr pin (pin 8) .This makesthe L293D usefulin a lot of applications. There are three things you should be aware of with the chip (1) The 0.7-voltdifferencebetweenVcc and Gnd and the selectedoutput level is due to the bipolar componentsusedin the manufactureof the chip;(2) The chip will dissipatea fair amount of heat when a

ot

nl 'Fl H

P.{ f\

t*i

batteries

P I C 1 2 F 6 ? 5 o r P I C 1 5 F 5 84 - b a s e d BS2 cotunand simulato! inte!face

s

c

chip

(see text )

AA alkaline

p

i{

dliver

1 B!eadboa!d-mountable SPST svritch

"-l {J

o

P 1 C 1 6 F 6 84

Figure l'f-9

Figure ll-8

Dual BS2 motor

264

l , e 3 P I C o l ' l C l JE x p e r i m e n t s f o n t h e E v i l

Dual DC motor H-bridse

Genius

motor is running(causedby the 1.4-voltdrop through the high and low pinsmultiplied by the currentpassing throughthe motors).Thetotal amountof power the chip can dissipatesafelyis 3 watts.It is a good idea to provide copperPCB heatsinkingto the chip via large fill or f'lood areason your PCB connectedto the groundpins to wick awayasmuch heat aspossible.(3) The L293D hashad spottyavailabilityover the past five years,with somemanufacturersdropping shipmentsof the chip while othershavebeenrampingup. The internal kickback diodes make the chip a lot more (alsoknown asthe L293), usefulthan doesthe 75,1410 which is pinout cornpatiblebut doesnot havethe diodeson the outputs. Onceyou havewired the circuit shownin Figure1108 on a breadboard(seeFigure11-9)and connectedit to a BS2 or simulatorapplication,you canbum asmBszMotor.asm into a PIC16F684and test out the oDerationof the two motors.

The BS2 comrnandand responseoperation is quite simple with values0x00to 0x3F being usedfor Motor 1 and values0x40to 0x7Fusedfor Motor 2. Like the previous applications,the middle values (0x20 and 0x60for Motor 1 andMotor 2, respectively)stop the motors,valuesgreaterthan the middle will causethem to turn forward,and valueslessthan the middle will causethe motorsto turn in the reversedirection.Like the previousexperiment'scode,the PWMs built into this application will have higher duty cycleswhen the motor valuesare further awayfrom the middle point. The motor software shown here could be usedasis for a BS2-controlled differentially driven (two motor, one on eachside)robot or be the basisof a differentially driven robot that is controlled using the single PIC16F684.The motor control code and PWM cyclecount incrementtake only Z cycles,leaving a thousandcyclesfor sensorand controloperationsof the robot.

14

X

U

o

,>

H.

:t

tU H l E

\s

taa ! I

w f-, "

ry (J

Experiment 99-Bipolar 5tepperMotorEontrol

H

frr

t$

m

,*&

P I C 1 5 F 6 84 1 L293D moto!

dlive.

chip

1 10k breadboard-mountable potentiometer I

}15 m

0.01 F!. eapacitor

1 B!eadboa!d-mountable Bipola! steppe! (see text)

DMM Solderiog

j.!oo

Four-cell crip

solder

AA alkaline

Needle-oose pliers

Klazy

,3

moto!

K

AA battely

LJ

battelies

1 Four-pj,n 0.1oo-inch header (see text )

Sci sso!s Glue

Ft

Ca!dboa!d

Wire clippers

( ,

o r"t

B!eadboard Wi,ring

kit

Steppermotorsare very populardevicesfor a variety of applicationsbecausethey canbe turned a specified amount,do not requireextemalgearing,and are generally very simple for which to designdriver circuitry.

lu

In this experimentand the next,I will introduceyou to the two mostcorrmon typesof steppermotors,unipolar and bipolar, and then to the driver circuitry and PIC MCU software that will first simply turn them and then

SectionEleven I ' l o t o n C o n t n o l

265

$

tst

l'! t r i !

{:

!J

s3,i rl t!

fft

tr-{ j-: &*i

.r,i

a I

control them usinga potentiometer,asI did with the DC motorsat the start of the section.To help you understandhow the softwareworks,I will first present you with C codefor driving the steppermotorsfollowed by assemblercode.

one or two coils be energizedat any time. Full stepping movesthe shaftby 90 degreesat a time,and only one setof coilsis energizedat any time.

Steppermotorshavea few notablecharacteristics: They consistof four (or more) coilsarrangedperpendicularlyto eachother (seeFigure11-10).Thesefour coilssurrounda magnetizedshaft,whichwill be either attractedor repelledwhen the coilsare energized. To turn the steppermotor, lhe coilsare energizedin a pattern that will causeit to turn in one directionor another.Becauseof the time requiredto energizethe coilsand becauseof the inertia (aswell asany load resistance)of the shaftand reductiongearingplaced on the shaftoutput,the speedof the steppermotor is much more limited than that of the DC motor.The reduction gearing reducesthe movement of the motor output ftom 45 or 90 degreesfor eachchangein position of the shaftto just a coupleof degreesor so to maximizethe torque output of the motor.Along with the slowerspeedof the steppermotor,the needto keepat leastone coil energizedat any one time will draw more currentthan doesthe DC motor. On the plus side,steppermotorscanbe moveda precise amount,and they producemuch more torque than doesa DC motor. There are two types of stepper motors commonly in use.The bipolar steppermotor will be presentedhere and consistsof four coils around the magnetizedshaft (seeFigure11-10).Thebipolar steppermotor canmost easilybe identifiedby four wirescomingout of the body of the notor with pairsof wiresconnected togetherthrougha smallresistance(whichis causedby the coils).The high-currentpush-pulldriversof the Hbridgeare usedto alternativelyturn the two setsof coilson and off aswell asturn them to differentpolarities.In Table11-1,I havelistedthe poladtiesfor the different coils to move the shaft by 45 degreesat a time.This is known ashalf stepping andrequires that

Table 11-1 Half-stepEoil EnBrsizationPatternfor a Bipolar 5tepFer Motor Step

Up-DouJnEoll

East-Wesl Eails

South

otr

South

South

otr

South

North

South

North

off

North

North

otr

North

South

North

InTable 11-1,the North and Southspecifications are arbitrary and are usedto indicatethat the polarity of the coils'magneticfieldschangesover the courseof the sequence. Also note that in Table11-1,I have emphasizedthe text of changingcoil (one coil changes in eachstep). To test out the informationin Table11-1,I createda circuit (seeFigure11-11)to drive a bipolar stepper motor andwired it on a breadboard(seeFigure11-12). With the steppermotor that I used,the connector attachedit to a doubleinline connectorthat could be pluggedinto the breadboard(similarto the onesused in the servoexperirnentselsewherein the book). Chancesare you will not be so lucky and you will have to solderthe individualpins to a singlepin inJine headerthat canbe pluggedinto the breadboard. Before burningthe PIC16F684with the following software,I suggestyou cut a sliverof cardboardasa pointer and Krazy Glue it to the end of the stepper

i.,r i

StepperMotor

:.-r **

ivj

-.:

{ii

j l

il . -oxi i1i

Figure ll-10

Bipolqr steppermotor control

266

l , A l P I C @l l C U E x p e r i m e n t s f o n t h e E v i I

Figure ll-'fl

Bipolar steppercircuit

6enius

PORTC = 0t CMCONo = ?t of,.E codrparalora / / $ri'r ANSEI = 0t // Turn off ADC TRIsc = 0b000011, // RCs,RC2 OutDulB

14 t

t NOP()t for (j = 0, NOP()t

j

< 21000r j++)i

PORTC = StepperTalrle i

Figure lf-le

Bipolar steppermotor testcircuit |

motor'soutput shaft(seeFigure11-12)so that you can clearly observethe movement of the stepper motor. When the circuitis built, you canburn a PIC16F684 with cstepper.c,which takesthe informationfrom Thble11-1and usesit to createa simpletablefor halfstepdriving the bipolar steppermotor. In between steps,thereis a quarterseconddelay,and if your applicationis wired correctly,you will seethe pointer you gluedto the steppermotor shafttuning through360 degrees(a degreeor so at a time).If you do not see this pattern,you will haveto rearrangethe wireson the breadboarduntil the motor startsworking correctly.(Do not desolderand resolderthe leadson the 0.100-inchheader.) *incluale - Tula cstepper.c /* ilhiE

Plogj.aln

is

a slel)pe!

Earakcar€ l{otea 3 PIC15E58{ Rurrdinq at { ltHz wilh oEclllator RC5:RC2 - St.eDDer Uotor Outl,uls

t

+ 1) % It

\o

// efrnw End. cstepper

\CI

The assemblylanguageversion of cStepper.cis asrnStepper.asmasfollows, Knowing that the code would neverbe longerthan 255instructions,I decidedto use a basic,not the general-case,table for the stepperpositions to simplify the coding. tiEle llotor

"aarsteDDe!

-

Prc15F684

Bipolar

steDlrer

Program OuEDutsa a a€w Bigolar g€qu€nc€ once every 250 ns.

b

t{

m (}

asmn. IJIST R=DEC rNcritDE .p15f 584. Lacn

s

Irternal

_coNFrc _EqlEN_oEF & _rEso_oFF & _BoD_og! & _CPD_OTE & _CP_OFF & _!{CI;RE_OFF & _PWRTE_ON& variabl€s CBLOCK 0x20 DIay, i E![DC t

-CONFIG ( INTIO & IIIDTDIS & PVIRIIEN & !{CI,R.DIS & I'WPROTECT \ & InIPROTECT & BORDIS & IESODIS & FCMDIS) t

= {0b011100, 0b010100. 0b000100,0b100100, 0b100000,0b101000, 0b111000,0b011000)t

r

PAGE uainLia€

uop

For

movlw

|

movwf

PORTC

<< 2

start Active Turrr

monwf, bsf, clrf movlw

lt

h{

K o

main( )

t

Ud

p,

Ealahdale t[otseE: PIC16F6g4 running at 4 lGIz usiDg tsbe raternal clock ratelnal Rea€t ia us€al RCs:RC2 - 1,293D gtepDer llolor Control

_IIIDT_OFF & _INIIOSCIO

[]

I

st€Dlrer

uyke Pr€alko 05.01.14

rllzke pleflko 05.01.15

uasigE€tl inl i = 0, jt consl chE! Stepger[able

I

Fr.

controlu

ThLs llotor

lfotot

baseal on "asmstepper.

, //

= (i

lil

o v' H o

,-r

== 1)

while(1

X

CUCONo STATUS, RPo ANSEL ^ 0x080 b'000011'

sectionEleven l l o t o n C o n t n o l

t

,

t

!

ICD D€bug with

Bit

2 : t

off

Collparalors

d E ecute out of, Bank 1 A11 BitE are Digrital RC5:RC2 are Outputa

267

b,t \J

F{

o

$.1 1J

c

o

U

t{

o {J o E ${

0, 0{ g{ 0,

novwf bcf

TRISC i 0x080 gEAltrUS,RPo

clrf

t

i ReturE rt €cution t Bank 0

i Retun i Value

IJooD:

H6r€

novlir

srcH ((25o0oo I 5l + 2561

novcrf movlw aaLlLw btfsc decfsz goto

DIay rJow ( (250000 -1 STATOS, Z Dla!., f $-3

movf call lrovwf

t, w StwitchReaal PORTC

goto

to

for

Next

nain ( )

{

5) + 2s6) t 250 mE Delay

/

= (t

PORTC = 0, CMCONo = 7t otf Compalatora / / \rrD, ANSEIJ=1<<3, // RA{ (A!13 ) ia tshe ADC IDDlrt

+ 1) % 8t

t

i

t i

Stayirg L! InalrucElonE

LooD

gwltchR€ed: aaLkdf

PcL,

atr

f

char StepperTable I I = {0b0U100, 0b010100, 0b000100,0b100100, 0b100000,0b101000, 0b111000,0b01r000)t corlst int On€ng = 83t codsl

riral

255

A.DCONo = 0b00001101t // Eur,r on the ,|IrC iluEtifieil // Bi-t. 7 - Left 5 - Us6 VDD // Bit // Bit 4.2 - nA4 / / BLt- f - Do not Stalt // SiE O - Turn on ADC ADCON1 = 0b0O010000, aa roac/8 // se].ect th€ clock TRISC = 0b000011, // RC5:RC2 Oulputg

b,011100,,b,010100,,b'000100,, b,100100, b,100000,,b,101000"b'111000,, b,011000,

alr

t{ d F{

o 91

..1

!q

I

Once I got the steppermoving consistentlyin one direction, I then expandedthe application so that a potentiometer would control the operation of the bipolarsteppermotor in the sameway asit would control the DC motors.cStepper2.cwascreatedto read the potentiometer wired to RA4 and then to change the dftection and the delay between stepsin the range of257 to 2ms.

Ehis

Prog:.a!

ia

Ol

Halalwsr€ NoreB:

o\

3::lii:::.-"""*s

lJ

c

c, g .Fl

t{

o

9{

X

-

Conlrol

ba6€i[

a gtepD6!

oa nasirst€DD€l

ltotor

Using

2.asm't.

Uotor OuEDuta Coatrol

unsiglneil unaigmetl

& IID4IDIS

& PIIRTEN & IICI,RDIS

& BORDIS & IESODIS

tnt t = 0, J, cha! Perlod,

& FCI.IDIS) t

olly

Move if

gofiFthllg

Ther€

{ (0x80

Lf

< Pefioal)

t P€riod i = (i

c (Periodl + 1) % 8t

-

0x80)

^ 0x7Pt

) //

61se R6verae i e (i

rPeriod' OK - 1) % It

//

POREC = SlepDerlable Uov€ Slepper

//

while DeLay at

,

(J = 0t J < Onelost j++); for P€rioal=gelLoal-1i // elthrd ) /l fL | // elihrt ) 2 / / EEd, cgleppar

I il ,

(0 l= Perl.oal) t{e!r PoaLlioD

{

ryk€ D!€alko 05.01.15

-CONFIG(IIITIO I'NPROTECT \ & I'NPRoIECT

//

ar { MHzwitsh rnt€rnar

RCs:RC2 - Slepl)€r RA{ - Pot€ntidlet€r

loop Foreve!

NOP0, f o r ( j = 0 t J < O n e m s , J + + )t NOPo, GODONE= 1' // starts A.Dc f o r ( J = 0 t j < O n e r n a t j++ ) t P€rLod = ADRESHT // R€adl Velu€ If (0!ra0 != P€riod)

€nat

#lnclutle cgt€9D€r 2.c /* a Pot

//

{

*J

a

( 1 == 1)

lrhile

Saq)I€

&

asmstepper2.asmis the assemblylanguageversion of cStepper2.c and performs exacdy the samefunction. Due to the nature of stepper motors (i.e.,having to delay a set amount between eachstep), I have not included a BS2 interface example.It is quite simple, due to the ability of the code to poll the BS2 clock line while it is delaying between steps.

frl

268

l , e 3 P I C o M C UE x p e r i m e n t s f o r

the EviI

6enius

tcl X l'zt

Experiment 100-UnipolarStepperMotorControl

{9 l-,1

tr.

Prc16F584 2N3904 NPN bipolar t!ansisto!s 1N914 (1N4148) siLicon diodes 100O res istors

fl\ ,-*

r-S

1 10k breadboard-mountable potentiomete! I DMM Soldelinq

Breadboa!d-mountable SPST switch

iron

Uoipolar stepper (see text )

solder Needle-nose $i!e

pI iels

Four-cel1 clip

clippers

Scissors Klazy

0.01 pF capacitor

AA alkaline

GLue

LJ moto!

AA battery batteties

Breadboard

Six-pin 0.10o-i.nch heade! (see text )

Wiring

Ca!dboa!d

kit

The unipolarsteppermotor is subtlydifferentfrom the bipolarmotor in how its four coilsare wired.Insteadof currentpassingthroughtwo coilsat a time,the unipolar steppermotor is designedwith a commonconnection betweeneachset of parallelcoilsthat allowseach coil to be turned on or off individually.The normal wiring configurationof the unipolarsteppermotor is s h o w ni n F i g u r el l - l 3 , w i l h t h ec o m m o nw i r e sc o n nectedto positivepower and the individualcoil wires beingpassedto opencollectordrivers,tuming the coils on in sequenceand drawingthe shafttoward one coil at a ttme. The unipolarsteppermotor is usuallydifferentiated by the nurnberof wirescomingfrom it. Although in Figure11-13I imply that five wirescomeftom the unipolarsteppermotor,thereare usuallysix.Eachpair of coilshasits own commonwire.Somesteppermotors havefive wirescomingout of them;theseseemto be hybrid unipolar/bipolarsteppermotors,whereeach pair of coilsis wired differently.In thesecases, you shouldtreat the steppermotorssimplyasbipolar.If you compareFigures11-13and 11-10,you shouldrealize that the unipolarsteppermotor canbe usedin exactlythe sameapplicationsasthe bipolar motor whenthe commonwiresare disconnectedand the four wiresleadingto an individualcoil are used.

I,

re

The differencesyou shouldbe awareof betweenthe two typesof steppermotorsare few.Becausethe unipolarmotor hasonly one coil activeinsteadof two, asin the bipolar rnotor,it doesn'thavethe sametorque asthe bipolar motor.On the plus side,the bipolar motor control circuitryis a lot simplerto program,simply pulsingeachcoil in sequence. Figure11-14showsthe circuit I cameup with for testingthe unipolarservomotor,and Figure11-15 showsit wired to a breadboard.In Fizure 11-14.vou

$, $*

{n

r+ {u

{s

PositivePower

ht ry !>

CoilContfols

r*

e.j

Figure 1'f-13 Unipolar steppermotor control

Section Eleven l ' l o t o r C o n t r o l

269

can seethe six-pin header to which the six unipolar stepper motol wires are soldered, with the common wires (found with a DMM resistancecheck)being placedin the middle of the connector.Along with soldeling the steppermotor wires to a headcr,you should also Krazy Glue ir cardboard pointer to the shaft of the steppermotol to observeits motion when you tcst it. Testirg the unipolar stepper motor is accomplished in exactlvthe same way as testingthe bipolar stepper motor: cStepper3.c will sequencethrough the coils, hopefully moving the caldboard pointer continuously. Again, if it doesn'1,n]ove the wircs to tltc control transistorsuntil it cloes.A simpler way of testingand decodingthe wiring is to touch the baseconnection (through thc l00O rcsistor)of cach transistor1()the Vcld rail of the breadboard.This will tell you which cir'cuit is wir.edto which pin. And thcn you can begin attachingthen in sequence,startingat:

lnain

*include cslepper 3.c /* This

Progra$

is

Figure lli5 Unipolor stepper motor circltit using NI'N tt ttnsistors as motot' contrel drivers

- turn based

Earalware Noles: PIC15F584 Running Oscillator RC5:RC2 - StePPer

at

a unipolar

Stepper

on " asmsteppe!

4 MIIZ with

Moto!

Mo€or

()

t POR4C = 0; CMCON0 = 7, ANSEIJ - 0, TRISC = 0b000011t

. asm" .

lrrternal

while(l Outputs

== 1)

// // //

r\rrn off conparators ?urfl off ADC RC5:RC2 Outputs

//

Irootrt Folever

{ NOP()i NOP()i

CONFIG(INTIO & WDTDIS & PMTEN UNPROTECT \ & UNPROTECT & AORDIS & IESODIS

= (Outputval Outputval" & 0x3C) ((1 << 5) == qrsnoao'.t, if = 1, << 2i outputval PORTC = Outputval;

& MCLRDIS &

char

outpueval

<< 1t

& FCMDIS)t I

unsigned

< 2 1 0 0 0r j + + ) ,

f o r ( i = 0 r i

05.01.15

= 1 << 2,

) //

// eliht^' E^d cslepper

"asmstepper

3.asm"

3 is

the

of

translaEion

As with the previousexperiment,I wrote codeto control the movementol the unipolarstcppcrmotor usinga potentiometer.The control soltwareis almost idcnticalto thatusedin the previousexperiment with a 2 to 257ms delayin the steppermotor movements. The C languageversionis calledcStepper4.c: #include 4.c - Control cstepper /* Motor using a Po! This

Progran

is

ttardvrare Nohes: PIC16F684 Runnins oscil.l-ator RCs:RC2 - Stepper RA{ - Potentioneter

Figufell-lq

Uttipolorteppercircuit

270

l , a 3 P I C @f l C U E x o e r i m e n t s f o r

baseal oll

at

a unipolar

"asrnstepper

4 MHz with

2.asm".

lnternal

Moto! Outputs Control

the Evil

Steppe!

6enius

if nyke pledko 05.01.15

'

((1 << 1) Outputval // fi

== Oulputval) = 1 << 5t

PORTC = Outpulvalr & WDTDIS & PWRTEN & MCI,RDIS & _CONFIG(IN:IIO ITNPROTECT \ a ITNPROTECT & BORDIS & IESODIS & FCMDIS) r

)

\)tn off conparators / / ""n to"il-rJii"-"o" rnput

ADcoNo = 0b00001101; // t,utn on the iqDC

// Rcs:Rc2 ourputs //

r

< onensr

i

i++)r

1r AtC // Start 0r i < onetnsr i++)r ADRESE' // Reaal value t= Peliod) rhere // Only Move if SonelhinE

(0x80

< Period)

//

Fondards

period = (period - oxso) ^ 0x7Fr outpulval = (outputval & 0x3c) a!

({r

<< o,

== uuEputvar,

ourDulval = t .. zt ) tt"t

>> 1'

,, *..r.rr.

4

asmstepper4.asmis the assemblylanguageversion of asmstepper4.asm. You might be wonderingwhy an intermediatevalue is usedfor storingand shiftingthe PORTC unipolar steppermotor positionvalue.Insteadof: Outputval,

anallw

b'111100'

btfsc iollw movwf

PORTC, 5 1 << 2 PORTC

novwf

OutputvaL

w

r Shift

the Saweal value

r Clear Out Shifteal t Bits r Ro11 Over? r Store Nevr activ€ t Bi! r Save New Set Bi!

uE)

Coil

I.oop Forever

<< 7.i

(

//

rlf 0r

j++)t

you might think that:

{ if

) // ti // elihw E!)d cstepper

rlf

tt P-il- 1 - r,afll .rlr
== while(1 { NoP( ) i (i = for NoP()i GODONE = for (i = Perioal = (0rr80 if

t

,

//

= r << 3i ANsETJ

!= Period) Delay at Ne$r PoBition

)

nain( ) t PoRrc= 0t

//

r4ove Steppe!

f o r ( j = 0 , j < O n e m st Peliotl=P€riotl-1; // elihw

= | << 2i char outputval unaisneal int jr unsiEneal char Perioalr consE int Onems = 83r

CIqCONo = 7r

(0

nrhile

//

- rperiodr oK

outputval = (clutputval & 0x3c)

PORTC, $

analrw btf5c

b'111100' PORTC, 5

iorlw rnovwf

1<< 2 PORTC

Up the Bil

Active

, ,

Shift Coil

i r t t i

rf Bit 5 was Set, Rolling over to Bit 2 Save New gteDper value

is more efficient. as it savesan instruction and a varia b l e .l h e p r o b l e mw i t h l h e s e c o n dm e l h o d r sl h a l l h e voltage acrossthe pin is at the one-halfvdd threshold (i.e.,the thresholdthat determinesif thepin ishighor lor.rand r.rhen it is read).and therefore the value is indeterminate. By putting a larger resistor on the base 6f the driver transistor, there should be a noticeably high voltage at the output pin. But I wanted to keep the circuit as general as possible and provide the maximum current switching possible so I left the 1000 resstor and added the variable.

S e c t i o nE l e v e n l ' l o t o n C o n t n o l

z, lL

Experiment l0l-Fladio-Control Model5ervo Control

1 Prc15F584 (any

1 0.01 ,uE capacitor tYpe) f

10k breadboa!d-mountable potentiometer

''-:

470C) 1o-pin

resi stor

1 10-LED balgraph

di splay

1 Servo connector text )

( see

i::.:j:l

DMM Oscilloscope Needle-nose !:

:,

Wiring

1 Radi.o control p 1ie!s

selvo

1 B!eadboard-mountable

kit

Three-cell clip

When you are fint gettingstadedwith robots,I highly recommendusingradio control servosfor drive motors.Servosare quite inexpensive($10or less,and cheaperthan many DC motor driver kits or gearhead motors),surprisinglypowerful,and very easyto wire into an applicationasyou canseefrom the schematic circuit for this experiment(seeFigure11-16),which I built on a breadboard(Figure11-17).Electrically,all you needis a 4.5-to 6-volt power supply,a line from a PIC MCU to drive it, alongwith a servoconnector built out of a coupleof three-position,0.1OO-inch, inline connectors(seeFigure1l-18). If you are looking to useservosfor driving a mobile robot,they will probablyhaveto be modifiedfor continuousrotation.In 123RoboticsExperiments for the Evil Geniw,I go throughthe basicstepsrequiredto

AA battely

modify a servofor continuousrotation.A quick Googlesearchshouldfind the informationfor your servosvery quickly.Eachmake and model of servo requiresslightlydifferentmodificationqand with several hundreddifferentservosavailable,it would be impossibleto try and list the modificationsfor each one here. The controlsignalpassedto the R/C servois known asa digitallyproportionaLsignal,whtchis quite a mouthful for somethingthat is really a modifiedPWM signal.Theperiod of the signalis 20 ms with a pulse and a duty cyclethat rangesfrom 1 ms to 2 ms,with the time betweenbeinsthe set positionof the servo.

:..

-:

I

-r,

i' :..:

I

i^. I

Figure1116 Servocircuit

272

Figure lllT Servocontrol circuit built on a breadboard

l , e 3 P I C @l ' l C l JE x p e r i m e n t s f o r

the EviI

6enius

.

PAGE Mainline

nop

i

For

:

ICD Debug .

cl.rf clrf

PORTA POR!rC

movlrf movlw

c!,IcoNo b,00001101, A.DCONO

bsf nrovfnr

SEATUS, RPo 0xD1

movwf mov1ff

OPTION REG ^ 0x80 1 << 3

morrwf movllr

ANSEL ^ 0x80 b,00010000,

morr'wf rnovlw monwf clrf bcf

ADCON1 ^ 0x80 b'011000' TRISA ^ 0r.80 TRISC ^ 0x80 STATUS, RPo

clrf

gervostate

i U€e Simple M/C , Stat€

Servo

movLw

0x80t

Start with in Middl"e

Servo

novwf

gervocount

t ,

rnovLw nov{rf movlw aatallw

IIIGE ((20000 / 5) DLay IJOW((20000 / 5) -1

btfsc alecfsz goto

sTATus, Dlay, f S-3

l

t conlDaratols

FiSUtel'f-18 Servo-to-breadboardconnectormade Irom two three-pinin-line connectorssoldered together

Someservosrequirea 1 to 1.5ms pulse,but you should be able to identify thesequite easilyusingthis circuit. And, if you havesucha servo,modifyingthe signal generatedby this experimentis quite easy. In this experiment,I usea potentiometerand the PIC16F684's ADC to specifythe positionof the servo. The valuereturnedfrom the potentiometeris displayedon eightof the 10LEDS built into an LED display bargraph.Thisfunctionwasodginallyput in to debugthe ADC operation,but I left it in becauseI liked seeingthe LEDs move with the servo.Thecode for this applicationis asmServo.asm. naamservo titl€ Prc15F584n ; . i t

-

Cotttlol1ing

lfhia Progiam uonitors a Pot (RA3) and movea a Servo at RiA5 Accolaling!.y. lhe Poaltlon of the Pot.

a Servo

a!

LEDg Inflicate

the

utrk€ Pledlko 04.L2.26 I,IST R=DEC rNcr.uDE "pl6f

58{. inc'

CONEIG _FC![EN_OFE & _IESO_OFF & _BOD OFF & CPD OEF & _CP_OEF & _MCI.RE_OFF E P!'IRFE ON & wrt! oEF & _rMtoscro VariabL€s CBLOCK 0x020 TerE), DLay Servocounl Servos!at'e ENDC

a

A.DC on RlA4

, Enable t IiIRo with i {x PleEcale! , RA4 (}N3 ) ADC , InDuts , i

Select ADC CLock as Eosc/8

i

BA4 /aA3

i AII

As Inputs

PORTC Outputs

.t"

RtA3

Eartl are Not€a: i PIC16F58{ runaing 6ts 4 MHz Using t Interaal Clock t ItA4 - Pot CdEnanal t RA5 - gervo Connection t servoPin PoRTA, 5 #alefine RC43RC0 - Bils 7:3 of LED Oulput r RA2 3RA0 - Bils 2:0 of, IED Output ,

r i

from

r EnabLe

LOOD: bsf cLrf, bcf, bsf btfsc gotso StaltADC: bsf bsf goto R€A'IADC: novf movwf andlw

i Wait for ADC Input , lo be valid

z t i

servoPin

5 Cycle Delay f,or 20 ma

t Output r Sisnal

!!MRo INIICON, ToIF INTCON, TOIE Servoslate, 0

, VJail

Loop

a Servo

for

Ov6!f1o{t

value i calculate r 1 ms PulBe

in

,

Start

t Reatl

iorfto

1 << 5

novwf rlf, novwf €rsapf andLw

PORTA Servocount, Tamp Temp, w 0x0F

r t t r

t

Section Eleven l l o t o r C o n t r o l

ADC

0

ADRESB, vt S€rvocount b'00000111'

w

-' .,...

Reaala.Dc ADCONo, GO S€rvoslate, ADCDone

'

ADC Value

Display lhe a.DC Value Make Sure gervoPifl Stays Bigh

r Neeal Top 5 BitE

273

btfsc iorlw bcf A.DCDone 3 nrovf btfsc aublct

r"€

btfaE gto!o movwf movf

f . :

.i

.|

.:-

b!f,aa golo

STA!!US, C 0x10 PORTC Servoslate,

0

t R€Peat

Se!-vocounl,

w

t Gel Reaal rdth i Servo Value

r Atld

{ .

ai i t

novLw etldl!.w btfsc decfsz goto

]Jow ((18000 -r STAIUS, Z Dlay. f $-3

goto

]JooD

/

+ 255) t vlanh

5)

20 ms LooD

Delay r 5 cycl€ 20 ms t for t ReDeats

],ooD

t{ake 1 t rf zero, t Tahe i! away fron

INTCON, TOIE TMRO INTCON, TOIF !t Servocounl,

lgait for overflow Bepeat tso g€ts 2 m6 Delay

INTCON, TOIF

TMRO INTCON, TOIE INTCON, TOIF

IIIGE Dlay

{s

Bits

Z

sTATgS, 1 0

ServoPin

bcf btfaB gloEo

Top

Finish€al gervo

wiuh

Wait

ovelfIow

for

the

((18000/s)+255)

Thereisn't a lot to this applicationthat shouldsurpriseyou.I useTMR0 to createthe delaysor 1,024 cyclesfor the 1 ms delay,and then I use it twice to create the servopositiondelay.Readingthe ADC takes placein the first 1 ms delay,asthe operationtakes about 15 /r.s.So there is no chanceof it taking longer than the delay,andthis makesthe servocontrol operation completelys€f-contoined.(Self-containedoperations will be discussed in the next experiment.)The threeTMR0 delaysend up lastinga total of 2 ms, which meansI simplyhaveto delayfor an additional 18ms to get a total PWM period of 20 ms.

Experiment 102-Multiple5ervoControl Softr-uare5tructure

=J 1 Prc15F684

:*' *-*

1

;

(any

0.01 pF capacito! tYpe)

10k breadboald-mountable potentj.ometer 470() 10-pin

resistor

srP I

1.0-LED bargraph

dispLay

Servo connecto!s Radio DMM

1

Osci lloscope

.=: l;i

Needle-nose pliers Wiring

control

Bteadboard-mouotable SPST switch three-cell clip

kit

servos

AA battery

3 AA batteries

: '

# 4

As I saidin the previousexperiment,servosare very easyto wire into a circuit.To add a secondservoto the previousexperirnent'scircuit,all you haveto do is add . an additionalservoconnectorasshownin Fisure 11.18.

274

In addition,the additionalcodeis surprisinglysimple, especiallyconsideringthat the secondservooperates completelyindependentlyof the first.

l , P 3 P I C @l l C U E x p e r i m e n t s f o n t h e E v i l

Genius

Servo2counl, ENDC

Servo2slat€,

Servo2Dlay tl

PAGE UainLine r

*?4

nop

Figure ll-19

Two-servocircuit

The codefor this experiment(asmservo2.asm)is a modification of the single-servoapplication, with code addedto hold the servoat one extremefor 600ms, move it to the other extreme,hold it therefor 600mq and then move it back to the original extreme.This operationis carriedout usinga softwarestatemachine that is built into the 1 ms initial pulsedelayof the servopulsgjust like the potentiometerreadingfor the first servo.Asboth servooperationstake 2 ms each, the final delayis reducedto 16 ms,so the loop (and eachservo'sPWM) periodremainsat 20 ms. rraamservo 2 titLe f ldr a PIC16F684rr i t r i r i

Controlling

two

a Servos

![hia Program ltorrLtors a Pot at RA3 (RA3) anfl nov€a a gervo at BA5 Accortlingly. LEDa Intlicate the PoEition of the Pot. A aecond aerro, coanected lo RCs will nove back p!€-Drogranrleal anil folth undl€r a ginp1e routine.

Hartbrar€ l{otea: t PIC16F68{ ruuing at { UEz Using the t r I|tternaL cLock RA4 - Po! CotElanal r RAs - S€rvo 1 Corrnection r servol.Pin PORra, 5 #alefine Rc5 - Servo 2 CoEnection r PORIE, 5 #define Servo2PiD RC4;RCo - Bila 7:3 of LED OutsDuts r BA2:RAo - Bits 2r0 of, LED OuEpul r

t ,

Myke Pletlko 04.L2.26 I.IST R=DEC IIi|CLUDErt916f694.inctr

_coNFIG _CPD-OFF _wD4!_OFr

& &

EC!|E!{_OEF & _IESO_OFF & _BOD-OFI' & CP OTF & _MCIJRE_OFF & _PWRTE_ON & INIOSCIO

Variablea t CBIOCK 0x020 Te![I), Dlay ServolCoun!,

clrf clrf movlw monwf novlw novwf

PORTA PORTC 7 otcoNo b'00001101, alcoNo

bsf movlw

STATUS, RPo 0xD1

t For

ICD

,

llrra

off

,

Elable

D6bug

t*, CodE)alators llDc

on Riall

1 :

mor of movlw movtdf, clrf bcf

I'MRo !d.th 4x , Enabl€ i Preacale! OPTION_REG ^ 0x80 1 << 3 r RArt (.BN3 ) A.DC hput AliIgEL ^ 0x80 b.00010000, r se1€ct A.Dc clock as t Foac/8 ADCON1 ^ 0x80 b,011000, r RA4/AA3 Aa Inputs TRISA ^ 0x80 TRISC ^ 0x80 PORTC Outputs r All STATSS, RPo

clrf

S€rvolgtate

lrovlv

0x80r

rrovwf

gervolcouat

cllf novl$

gervo2stsate

movlrf

gervo2Dlay

movlw movwf movLw adltlLw

EreB ((2oooo / 5> + 256> Dlay Low ((20000 / 5l + 2561 -1f,or ADC Input t wait t to be Va]-ial STATUS, Z Dlel', f DeIaY Lo<'E) S-3 ; 5 C!'cle t f,or 20 lla

monwf movlw mor cf movlw

btsfac atecfsz goto

LooP: bEf

t , i r

0x20

r stsay in ; DUU InS

gervolPin

TllRo clrf bcf INTCON, ToIa bgl INTCON, ToIE btf8c S€reo1statse, golo ReatlADc SlaltADC I A.DCONo, GO baf gereolstale, bEf goto ADCDone R€adADC r movf ADRESH, $ gervolcount nov\sf aaallw b,00000111, LorLw

1 << 5

mo"lrf rlf movwf swaDf

PORTA gervo].counts, Tenp TetDp,

use SimpL€ state M/c gtart wilh Miildl€

t Oulput , sigmal

*

servo

in

fo!

c-,,, ir"

{U

cn /n 11

a Servo

Overflow

\-, q

0

t

sEarE

.-fr F3

Arrc

0 r Reaal LDC Value

r DisDlay

the

t KeeD Servo

r Neeal Top

ADc ConlroL

5 Bits

w

Section Eleven [ ' l ot o r C o n t r o I

!I

g€rvo

Po6ilion

, vfaits for

w

F-r

275

aaal].$ btf,ac iorlw movwf bcf ADCDone: rnovf

0x0F STAIIUS, C 0x10 PORTC S€reolgtate,

0

t Repeal

Servolcount,

w

i

goto servo2Done gervo2stale, lncf novl$ ot<020 genrozDlay novcrf g€rvozDone goto Servo2gEate 0:

r Aald Top Bil

Reatl

Get

g€rvo

with

i Value

FI

o

f{ JJ

g

o

U

o ${

0)

(n o F-f

P{

.Fl

{J F{

btf,Bc movhr aubllr

STATUS, 1 0

Z

btfaa goto novwf bcf movf,

INTCON, TOIF $-1 T!m.o INTCON, I0IF gorvolcount,

btfsa golo bcf

INACON, ToIF $-1 g€rvo1Pl.n

novlrf bcf btfaa goto

lltRo IN:!CON, T0I! rNTcoN, T0r! $-1

bBf

g6rvo2Pin

r If zero, Make 1 , Iake lt away frofir

w

, ,

t t

clrf TllRo bcf INTCON, TOIT bsf INICOII, ToIE g€rvo2gtat€, eovf xorhr 0 gTATttg, z btfac g€rvo2state_o goto laorlvr 1 ^ 0 btfsc STATUS, Z gervo2gtat€_l goto xollhr 2 ^ tblfac STATUS, Z g€rvo2gtat€_2 goto s€rvo2gEat€_3:

I

I

f\

o Fl

{J

g 0,

E

'rl

tt 0) 9r

X

bcf STATgg, C gervo2Dlay, rlf noverf Tetqp rlf rerE, f rlf TetE, f rlf TetE, f lrovf t6tqr, rtr gTArVS, C blfsc novhr or.FF novwf Servo2counl alecfsz Servo2Dlay, goto Servo2Doa€ cllf Selvo2slate novlw 0x2O gefiro2Dlay lrovlrf gervo2Done goto servo2gtate_1: bcf rlf r[ovwf rlf rlf llf novf btsfac novlrr aulchr novwf alecfsz

gTATug, C gervo2Dlay,

0

w

i

gervo2 g€rvo

!ou!

lgith

for

t WaLt

Overflow

coale

s€rvo2count s6rvo2Dlay, gervo2Done

novlrf incf gtoto

s6lvo2D].ay S€rvo2gtate, Servo2Done

Baaea[ on

fo!

2 slat€s

r llulliDly

blz 15

f i

At

Extrem€

f

0x10

gervo2Dlay nrovwf g€fvo2gtete, incf Servo2Doner nrovf s€rvo2counts,

i llove to ,. Extreme

Oth€r

f w

i i

Get R€aal vith VaLue

btfsc novLw

sTATug, z 1

sublw

0

btf6s goto novwf bcf llovf,

r!q!co!{, TorF S-1 TllRo IN!!CO!{, !!oIF Servo2count,

btfas goto bcf

rN:!coN, TorF S-1 servo2Pin

novwf bcf blf,aa goto

T!{Ro INIICON, !!oIF INIICON, ToIF 9-1

movlw novwf novlw

HIGH ((16000 | 5l + 2s5l Dlay l.oll ((15000 I 5) + 255, -1 t want 20 na

adtUw blfBc STA!!US, Z alecfEz D1ay, f g o t s oS - 3

Exlleme Store

f

goto

At

Other

!{ake 1 lo i Lf. z.ro, Negatioa Elror t Avolil array frorn t Take it

IJooP

w

for Ctv€rflow t weil i R€trreat to g€t 2 ns i DEIEY

t ;

Finished gervo

r I4Iai!

for

witsb

tshe

overflow

LooD

r 5 C!t'c1€ Delay 20 mE ; fo! i Repeat

l.oop

Extrdte enA

w

t cioLng to t Extrdn€

oth€r

r lrultiDly

b!'

t Al

16

Exlrqle

r Negate il t Olh€rwige

This application demonstratesthat you can create surprisingly sophisticatedoperations in the PIC MCU even when you have a limited amount of time to create them.The secondservostatemachinerequires around 33 instruction cyclesto control the servo;about 30 times fewer cyclesthan are available.With many robot applications,it isn't unusual to seea variety of different functions "tucked inside" the servo delay loops and using the PIC MCU's built-in timers.

Stor€

f

{rl 276

S€firo

Otr€rflolt

ger,uo

t Oth€FdiE€

Poinl

Orisinal

t !4ove !o t ExEl.dr€

1

oligirel

t Wait

0x10

gervo2cou,lt gervo2Dlay, gervo2Doae

at Extrqle

f

s€rvo2s!ate_2: lrovhr OxFr novwf dlecfsz goto novlrd

t wait

, Al

th€

, eoing to i E rlr€ne

t At

TenD T6nD, f Tern9, f T€tqr, f T6q), rt S!!Al[oa, c oxEF 0 g€rvo2count S€rvo2Dlay,

qlnLsh€al gervo

t Wail

Fl

x

r WaLt for Overflow t ReD€al to g€t 2 na t DeLay

clrf alocfaz goto lrovlv

f

1 , , e 3P I C @I ' l C UE x p e r i m e n t s f o n t h e E v i l

Genius

ffi

Experiment103-Tr-uo-seruo FlobctBase uJithBsa lnterface

!,,

ar

iv &!!

s-? P r c 1 5 F 5 84 0. 01 /rF capacito! type)

(anY

\ I,J !*{

Servo connecto!s

2 Radio control

selvos

1 Breadboa!d-mountable SPST switch AA battely

Three-cell clip

P I C 1 2 F 6 ? 5 o ! P t C 1 6 F 6 84 based BS2 coftnaod simulator interface

AA battelies

:I

1 Breadboa!d

DMM Osci Iloscope Needle-nose pliels Wiridg

w

kit

In the previoustwo experiments, the full eighfbit valueof the ADC wasusedto specifl the positionof a servo,and this workedquite well.As will be shownin this experiment,the BS2interface,asdesigned,cannot sendan eight-bitpositionvaluealongwith a command value,which limits how the controllingse os can move.Along with the restrictionon absolutenumber of bits that canbe sent,thereis alsoa restrictionon whendatacanbe sentto the receiver.Thisfurther reduceshow datacanbe sentto the servos.In this experiment, I will demonstrateone way of solving theseissuesand discusshow to decideon the best methodoI implementing this[unctjon in your own applications. Using the programbaseof the previousexperiment, I changedthe applicationso that if a BS2command camein whenthe servoswerebeingwritten to, the commandwould be ignored.If the servocommandwas processed while the servoswereactive,the pulsewould be extended,which would resultin an unexpected movecommand.In Figure11-20,this is indicatedby the shadedWindowsin which receivedcommandsare accepted. The problemwith this methodoccurswhen the BS2commandis active,the PIC MCU softwarehas finishedsendingthe controlpulsesto the servoqand a low BS2clockis encountered. The protocolusedto sendthe datato the servo-controllinsPIC devicemust

be ableto sensethat the commandis not comDleteand shouldbe ignored. The basicBS2command-interface softwaredoes handlea goodportion of this functionby terminating receptionif a timeout happenswhile waitingfor additional clockpulses.In additionto this basiccapabllity,a methodis requiredto determinewhetheror not the datais valid and to feed backto the BS2an indicator of whetheror not the commandhasbeenaccepted. The way I solvedtheseissueswasto sendonly a responsecommandto the PIC16F684, with certain restrictions. The first restrictionis that asa response command,bit 7 of the eightbits sent,is alwaysset.If it is low,the commandwill haveto be ignored.Because thereare two servos,a bit mustbe allocatedto specily which servothe commandis beingsentto (I usedbit 8 of the incomingdatapacket).Finally,to ensurethe datais valid,the lastbit mustbe zero (the reasonswhy will be explainedin a moment).Thisreducesthe number of positionbits to five and providesthe servoswith onlv 32 differentoositionstates.

ra f 5 I

;

r-qJ !

:

*"q'*

! i

*E

&: servotL Servoz

Figure l1-?0

i;,

fl

fl

Servoavailable

SectionEleven I ' l o to r ( o n t r o I

271

nl

d

na +J ta

o

e6

o ${

The reasonfor making the least significant bit zero is to handlethe casewheredata is partiallysentwhen the data-readwindow becomesactive and someof the bits are read.After sendingeight bits, the BS2 will put its data pin into input mode,but the PIC MCU will still be reading the primary command data, and its data pin will be in input modealso.Becausethe PIC MCU data pin is pulled up,a 1 would be receivedasthe leastsignificant bit, which is invalid. Therefore the PIC16F684 controlling the application would reject the command. I decidedto usethe responsecommandinsteadof the straight eight-bit command becauseif the received commandwasinvalid,the PIC16F684would not respond(becausethe commandhad bit 7 reset)or becausebit 0 wasset. In the casewhere eight valid bits werereceived,the PIC16F684would attemptto respondwith the eight times the servo-positionvalue sent or with 0xA5 to indicate that the commandwas (i.e.,anythingother than not received.These responses eight times the servo position) indicate to the sending BS2or BS2 simulatorthat that the commandwasnot receivedand the servopositioninformationhasnot changed. This method, while seeminglycomplex,worked very well on the prototypecircuit (seeFigue 11-21)used with the asmBS2Servo.asm softwareand connectedto

]To Servo 1

Figure ll-al

BS2 two-servocircuit

a BS2 simulator. If the position information was invalidly received,the LCD display on the BS2 simulator would either have an invalid value or a value of 0xA5. When deciding how to implement a communications protocol like this one, a number of issuesshould be considered, and,asI will discussin the next section, a number of different options should be reviewed.In Table 11-2,I have listed four options for implementing a BS2 command and their comments.While the methodpresentedhereisn't what I would considerthe best,it was the easiestto implement with an unmodified BS2 simulator on a workbench.

(,

aI o

F F{ II

fn 16

Table 11-2 EomparlngDlfferentMethodEof sending servo PositionBaia from a BSa or simulalor ODerationSeauence

Eommentg

Expandthe data packet

16-bitdata word from BS2

Add a "handshaking"line from the servocontrollerto the BS2

After se o commandscomplete,enable "Bs2Receive"pin until5 ms beforenext set of servopulses

will requirecustomsoftwareinsteadof shiftin and shiftoutcommandsThe resultingwaveformwill not be compatiblewith existingsoftwa.e. Disable"Bs2Receive"5 ms beforenext servopulsesto

Sendfive-bit servopositionalong with servoand resetbit 0

Sendservoposition,expect position* 8 returned

avoid changing software timing. Eliminates reset bit 0 and gives a maximum of seven servo position bits. Adds requirementsfor an additionalpin to be used. Method usedhere:OnIy frve positionbits but couldbe usedfor mobile robot d vingse os.

Sendtwo packetswith eight bits 1.Sendhigh four bits of servoposition Longestpacketlengthbut properly receivedfour bit of positiondata for specifiedservo 2. Sendlow four bits of servoposition valuescould be savedto avoid resendingdata.Thisis 3, Sendrcsponsecommandto verify servo the most difficult method to test on the workbenchwith positioninformationreceived the BS2simulators

{.}

H

.r{

t{ P-,

X

278

l , e 3 P I C @I ' l C UE x p e r i m e n t s f o r

the Evil

6enius

Section

Twelve

SolvingProgramming ProblemE in PIE@ Microcontroller FssemblgLanguage Thereis a certainirony with the first pointithe point of the exercisewasto help the studentbetter understandhow to programthe PIC MCU in assembly language. In the previoussectiongthe PIC MCU instructionsand basicprogrammingbuildingblocks werepresentedand shouldhavebeenfairly easyto work throughsuccessfu lly.The programming assignmentslistedhere,althoughusingthe skillsdeveloped in the previoussections, force the developerto choose the bestinstructionsand codesnippetsto implement A good test of your ability to developassemblyJanthe applications. This uncertaintycan be daunting. guageapplicationsis to attemptto developprograms The bestway to becomemore familiar with PIC in assemblythat performfunctionsthat are normally MCU assembly-language programmingis to actually programmedin highJevellanguages. The classof prodo it.This meansyou shouldsimplystartwriting code. gramsthat might be most effectivefor this experiment It may not work properly,but asyou think throughthe includestraditionalmathematicalprogrammingprobprocessof putting down instructionsthat carry out spelemsand conversions that don't requirea lot of learncific tasksand seethem execute,you'll learn from your ing to understandhow they work, but may requirea mistakes. You'll learn how to recognizethat it isn't bit of thinking to solvethem effectively. working,be ableto identify the instructionsthat are The problemsandsolutionslistedin this section producingthe wrong result,and then changethem so wereoriginallydevelopedfor grade12 (senioryear) the applicationcodeperformsthe task that you high schoolstudentsto leam about assemblyJanguage wanted.Theseskillsdo not comefrom readinga book programming.The assignments themselvesare quite and following an exampleiyouhaveto force yourself simple.None requiremore than 50 assemblysource to comeup with somecodeon your own and get it codelines.Eachstudentwasgivenone of the assignto work. mentslistedbelow and the taskof researchingthe The MPLAB IDE combinesthe editor,compiler/ requirementand then comingup with the "best" soluassembler, and simulatorin one packageand is a very tion for it. Despitethe advancedlevel of the students powerfuldevelopmenttool that you will haveto and the simplicityof the final applicationEthe students becomefamiliar with. So far in this book,I haveintrohad a surprisingamountof difficulty comingup with ducedyou to its basiccapabilitiesand givenyou a few the solutionsto the assignments. hints on how to useit for applicationdevelopment,but I believethe reasonsfor the difficultiesare asfolyou'll haveto learn how to useand customizeit so it lows: works mostefficientlyfor you.None of the applicationspresentedin this section(and,asI haveargued, . Uncertaintywith PIC MCU assemblylanguage none of the applicationsin the book canbe accomANdthE MPLAB@IDE plishedwithout taking advantageof the MPLAB IDE . Difficultytranslatingmathematicalconcepts simulator). into programmingalgorithms Tianslatingmathematicalconceptsinto program. Inexperiencein evaluatingprogrammingalgoming algorithmsrequiresan explicitunderstandingof dthms both the requirementsand the potentialsolution.For you will haveto do someresearch theseapplications,

279

L.

. r-l {J

d U

.Fl ,-|

9{ .l.1

dJ r-{

5

E ..1

m I

{J

bt

. r.l

kl

and be ableto understandwhat is beingpresented.I recommend keeping the mathematicsand programming textbookshandyand usinga searchenginelike Google to researchdifferent explanationsof the mathematical concepts Do not fall into the trap of using only one sourceof information. Although one source may be good for someinformation, there will definitely be better sourcesfor other information. And as with any research,don't treat everythingyou find (whetherit's from booksor the Internet) asbeing100 percent correct, Check your sourcesand get more than one sourceif possible. When you understandboth the application's requirementsandthe theorybehindthe solution,look for multiple waysof implementing the solution. Use this asyour basisfor determining what is best.When I am given a task, I try to come up with three different waysof accomplishingit. Chancesare one solution will becomeimmediately obvious,but if I pushmyself to look for multiple solutions,I'll either come up with a better solution,or an improvementto your original solution. Before going on to the assignmentsand their solutions,I wanted to saya few words about what makesa solutionthe "best" solution.Tryto avoidsimplistic like "the shortestprogram"or "the measurements fastestprogram,"becausethey don't reflectthe dynamic nature of real-world application programming. Instead,try to articulate your requirements as clearly aspossiblein a defined area as a requirement continuum,likethe one shownin Figure12-1.By definingthis area,you'll be ableto more clearlyand easilydefineexecutionspeed,amountof program memory,and variablesthat are availableto the prob-

Code Size Smallest Progaam

'Best"Solution SolutionArea Meeling Requirements

Speed 'f Figure ?-'f Besttriangle

lem.The solutionsthat lie outsidethis areacanbe immediatelyrejected,and the bestsolutioncanbe more easilyidentified. Before working through each experiment of this section,I suggestyou try to come up with your own solution to the problem (even going asfar aswriting your own solutionandcomparingit to mine).In most of the experiment write-ups,I have presentedmultiple waysthe problemcanbe solvedaswell assuggested someadditional experimentsyou can write. By doing this,you will get a better understandingof how the solution works and you'll becomemore familiar with programmingand the PIC MCU assembly-language MPLAB IDE. Chancesare you'll alsocomeup with better solutionsthan the onesthat I cameuo with.

! a

Experiment 10U-Eieht-Bit Multiplication r-uitha l6-8it Product

{tr O FI {J

multiplication asrepeatedaddition and add the multiplicandmultiplier numberof timesasI showin the examplebelow:

0,

trasnMultlDly tsitle aalttition.

c

g

t Thia l)logram uses leDeateal litultiplication. r impledleat

"l.1

t-l

rrcl Equival€nt

(,

9.{

x

1 - uulEiply

The fist assignment,multiplying two eight-bit numbers togetherto form a 16-bitproduct,canbe accomplished a number of different ways.The most obvious way of doingthis is to go back to the definition of

280

(!ftrltip1ier

aaLlition

to

Codle;

Proaluct = 0t = valuelt uultiplie! = valu€2t llultiplicantl $hj.le

Repeat€al

UEing

!= 0l

l , P 3 P I C @l ' l C l JE x o e r i m e n t s f o n t h e E v i l

ll

15-Bit

//

Proaluct value

aalal Each velue

Genius

t

Proalucl = Ploaluct + ltultiplicanal, // Jrtltl DlulEtpltcandl to Proilucts = !4u1tiD1ie! - 1t Multil)].i€i // Decrement MuLliplie! Couat //

|

lrhtle

iof (1 -=

!1,

ll

Halfl$are No!€a: PIC16F68{ runalig

FiniEh€d,

at

Loop

{ MEz in

Eor€ve!

Sinulator

lryk€ Plealko 04.08.18

8'1100' ldu1tip1i€r 8'11000' ltultiplier 8'110000' tluLtiDLier + 8'1100000' !,tultiplier

LIST R=DEC INCIJTDE I'p16f 58{. incn r variaSlea cBr,ocK 0x20 Ploaluct:2 UultLDlicanal,

, !'inlEheal Resul! i valuea for t Pfocessingr

Multil)lier

org

of

Multiply

1

0 r hitiaLize t valiebL€s

clrf I[ov1tr novwf, Inov1lr rnovwf llovf, btfEc goto LooP: atlikdf btfac incf tl€cfBz golo EnfllJoop: goto

Proaluct + 1 47 I'lultiplIe! 35 Multiplicanal l.tulti91i6r, f STATUS, Z Enflloop Proalucl,

f

STATUS, C Proaluct + 1, f uultiDli€r, f

, Valuel

<-

47

, Value2

<-

35 == 0?

, MultiDli€r i

Yes,

Protluct

= 0

t Aildl Multiplicanal Protluct i 15-Bit

I,ooD

UultiDLier t Decrenent i andl RepeaE !=0 , while

s

i

= 8'1100'

<- Bit

0 of

= 8'00000'

<- Bit

1 of

= 8'110000'

<- Bit

2 of

<- Bit

3 of

= 8'0000000'

to

r,ooD

5ection Tulelve

X

'6

o

y,! f-.,

r* ry

<- Plduct

, F

50)

= tlultipLie! x !tultip1icanal - ( (MultiDlier & 0x00F) + (Uultiplier 0x0F0)) x ( (Multiplicand & 0x00F) (l{trllip].icand & 0x080) )

& +

and then multiplying them together usingrtrst, outside, inside,last (FOIL). The program that I cameup with is "asmMultiply2.asm." This lastprogramrequiresabout 12timesthe number of instructionsasthe previousexamplesand one more file register byte for the Temp variable.What it hasin its favor is that it always execltes in 104instruction cycles. The conditionalassemblystatements(i.e., the if, else,and endif directives)selectbetweensetting the PCLATH register for the table jump or delaying a cycle so no difference existsin how the code executes basedon whereit is located. Despiterequiringmanytirnesmore instructionsand not being substantially faster than the shifting

S o l v i n g P r o g n a m inn g P r o b l e m s

rc Ffi }J'

{q l r

I

s

r.. ,7,

A

F l r

end

This solutioncouldbe consideredbestby some measurements becauseit requiresonly 15 instructions. But a fundamental problem existswith this method: The number of cyclesneededto multiply two values togetherrangesfrom 10 to 1,539dependingon the value of multiplier. For some applications,this is not a problem.But for many applicationEespeciallythose involvedwith real-timeoperations(suchasrobots), this variability and potentially long execution time couldbe a significantproblem. When you first learnedto multiply,you may have doneit like the exampleapplicationhasdone it, but after a while,you useda more sophisticated methodin which the multiplicand was shifted to the left accord-

ftl

$

"asmMultiply3.asm"showshow this is implemented. If you were to test the secondapplication with different multipliers, you would discoverthat it generally executesin 90 to 110 instruction rycles.This is a huge improvementin speedand predictability,with only six instructions(andno file registervariables)addedto the first example. I wantedto seeif I couldimproveupon the execution speedof the secondmultiplication example by multiplying larger digits.Four bits, or hexadecimaldigits,seemedlike a naturalprogression, and a table was built with the products for all the possiblefour-bit multipliers and multiplicands.With this table in place,I then multipliedthe two eight-bitnumbersby breaking up the multiplier and multiplicandso that they look like the binomialexpansion: Proaluct

finisheal,

<dot> 1 (ser) 0 (R€set) 1 (Set) 0 (Reael)

B'0111100, (Deciral

ENDC PAGE , Maialiae

ing to the multiplier digit by which it is being multiplied.Thismethodis actuallyvery easyto implement in PIC MCU assemblyif you assumethat eachdigit is a bit. The productof a multiplier digit (or bit) and the multiplicand can be either the multiplicand or zero, and shifting the multiplicand by the multiplier digit is accomplishedby simply shifting the multiplicand. For example,to mulriply 12 (8'1100') by 5 (8'0101') in binary,it would look like:

28L

,-, "

t?3 F

,-, "

ta

,-,.

tJ

ltr

:, "-4

ru

multiplicationalgorithm,you shouldrememberthis methodbecausethe theorybehindit canbe usedfor processorsthat have a built-in eight-bit multiplication instruction(suchasthe Microchip PIC18seriesof microcontrollers). By usingthe methodologyshownin this example,you can create a 16-bit multiplication routinethat executesin just a few instructions. After creatingthesethreeapplications, we cannow askthe question:which one is "best"? For virtually all

applications, the secondexample(asmMultiply2) would be consideredbestin termsof executionspeed and instruction optimization. The last example would be consideredbestonly for applicationswherethe constantspeedis requiredor whereit wasknown beforehand that sizeof the multiplier and multiplicand neverexceeds15 (requiringno more than four bits).In the latter case,the eight-bitproduct would be found in a constant 13 cycles.

$*{

a

ExFeriment 105-Bivisionof a 1E-Bit Valuebg

a

\&;

an E i g h t-B iVa t lue "aamDivide litle arl g Bit Valuerl

'"H

!i

. *., a : 1

i

{JJ

rJ

Programmingfor divisionroutineshasmanyof the samecharacteristicsasprogramming for multiplication. There are severalwaysof doing it, and each methodhasdifferentcharacteristics that make them bestfor certainapplications. In this experiment,Iwill look at a numberof differentwaysof implementing division operations and comment on their effectiveness.The routinesthat are presentedhere are for positive,nonzero integers.I will discussmaking these routineswork in the generalcaseat the end of the experiment. If multiplicationcanbe describedasrepeatedaddition, then,asits inverseoperation,dlvisioncanbe describedasrepeatedsubtraction,subtractionbeing the inverseof addition.A simpledivisionroutine can be built from a subtractionroutine that repeatedlysubtractsthe divisorinto the dividenduntil the dividendis lessthan the divisor.T\e quofunt is inuementedduring eachloop,and at the end of the routine is equalto the numberof timesthe divisorcanbe taken away from the dividend. When the dividend is lessthan the divisor, it is passedback to the calling routine asthe remainder.A sampleprogramthat implementsdivision in thiswav follows:

1 -

Dividle

a 15 Bil

r r t t

ThiB program finalE tshe quotienl redlainaler for iliviatins a 16-bil value value frodr a! 8-bit by repeateil subtraclion.

r

'C"

Equlvalent

anal

Cot[€:

= Divialend = 123{5t Rdrainale! = 0; la 15 Bita // Ouotleat Ouotient = 47, DlvLso! is 16 BitE // Dllflaot while

( Remalntl€r

>= Diviaor)

{

- DivLEolt = Reneinaler value // Take avay Divlsor Quotient=Quotient+1, // Incr€neat ouotients j // et L}rw Remaintl€r

//

Quotienl

while

and Diviit€ntl

a!€

correct

(1 == 1), //

Ealthrare Note6: PIC15F58{ runaing

Finished,

at

Loop

Foreve!

4 v,J, z Ln Simulator

!&.ke Predlko 0{.04.13 IJIST R=DEC rNcrJIrDE np15f 5811.lnc" t valiable6 CBIJOCK 0x20 R€[lainaler:2, Divialenat : 2 DiviEo! Temp ENf,IC

Quotient:

2

:,4

282

valu€

l , e l P I C @H C U E x o e r i m e n t s f o n t h e E v i l

Genius

bl'

PAGE r !!al|rll.ae org

of

Diviale

0

novllr

high

123{5

t Inilialize veriables

novwf trovwf rdovhr novnf nrovwf, movhr mov f

+ 1 Divialead R€maiudle! + 1 low 12345 Diviatenit R€[rainal€r {7 Diviaor

clrf clrf

Quoli€nt Quolient

+ 1

Diviileloop! movf R€lEj.ntl€r

+ 1,

novlrf rnovf aublrf bEfa5

TedE) DlvLaor, w Re$ainater, w STATug, C

alecf btfac

TdE), TdE),

r If USB of (Redlaintte! l= 1 ; - Divisor) r then Subtract if set tshen t EIse, t Finiah€dl

DivialeEnd

tnovwf

R€eaiuale!

movf movwf

T€rlp, w Reneinaler

+ 1

incf

Quotient,

f

btfsc incf

STAIIUS, Z + 1, ouotient

goto

Divitleloop : $

Diviso! r gubtract anal r from Rdlainil€r t E e e i f > = 0

; If Carr!. Set, Lolt r Bt t€ of R€rEintter

f 7

goto

DivialeEnil goto

rtr

t t

Save ResulEE sulctracEion

i Increm€nl t Quotienl

of

Eh€

f

r FLalEheal,

]JooD

€nil

When you look throughthe diyisionby a repeated subtraction subroutine,you'll seethat I subtract the divisorfrom the dividendto seeif the resultis negative (andthe dividendcanthen be referredto asthe remainder).Ifthe resultis positive,this resultis saved asthe new dividendinsteadof calculatinsa new dividend. Repeatedly subtracting the diyisor from a number is potentially the slowestmethod of implementing division,justasrepeatedadditionis a fairly poor way of implementingmultiplication.Division canbe implemented in a similar manner to multiplication by fhst shifting the diyisor up so it is greater than the dividend and then shifting down and testing to seeif the shifted divisoris lessthan the dividend.If the shifteddivisoris

lessthan or equal to the dividend, then the divisor is taken away from the dividend, and the shifted amount is addedto the quotient.I find it is easierto understand how the algorithm works by coding it out as I havein "asmDivide2.asm." This rnethod and code for diyision is probably the most efficient and suitable for virtually all applications. Even though it requires twice the number of instructions asthe repeatedsubtractionmethodrequires,it executesreasonablyquickly and accurately. Going back to your grade schoolmathematics,you probably remember there is another way of dividing onenumberinto another:Thatis,write the numberas a fraction and multiply the inverse of the denominator with the numerator: A dividedby

B = A / B = A x

ll

/ B)

And althoughyou may rememberit, you may not seeits applicabilityimmediately.ThePIC MCU's processordoesnot havethe floating-pointnumber capability required to calculatethe reciprocal of B (or 1/B).Thisis true,but a positivenumbercanbe producedif, insteadof dividingthe divisorinto 1,it is dividedinto a much largernumber-such as256.This would turn the previousequationinto:

['J

X

u

s

rl

F. '.a tv 11

# O

tn t?

**r"

v.

A divided by B = A / B= tA X {1 / B)l x 1 2 5 6 / 2 5 6) = l A x ( 1 0 0 / B ) l x 2 5 6

Although this is an improvement,you may also be wondering why I would go through the extra work of dividing the divisor into somenumber and then multiplying the reciprocal of the divisor by the dividend.The answer:This method makesthe most sensewhen you are working with a constantdivisor. Calculating the reciprocal of B can be implemented by the assembler's built-in constantcalculator,and once the reciprocal has been calculatedasa constant,it can then be multiplied with the dividend,asI showin "asmDivide3.asm." This methodusesabout60 percentof the instructions of the full division routine and executesin less than a quarter of the number of cycles.Note that divisionby 256is accomplished by simplytaking the upper byte of a two-byte number.This routine is simply not asaccurateasthe other methods;no remainderis produced and the quotient is typically off by 5 percent. This method is suited for applicationswhere the divisoris a constantand known,and the dividendgoes through only the division processingstep.Situations where this division routine is best suited include convertinguserand sensorinput datafor storage/ processing.

Ht

pl lJ

{p\ I

,

w }J.

*

pr H IR

5ection Luelve

Solving Programm i ng Pnoblems

283

Remember,the casewherethe divisoris zero is generallyconsideredinvalid.In many processors with built-in division circuitry if a divisor equal to zero is encountered, an error is flagged.Asnoted at the start of this experiment,none of the threemethodsof division shownhere will work for this case(and will either neverend or causea build-timeerror). To check a single-bytedivisor, you can sirnply run the value through the PIC MCU's Algorithm,flogic Unit (ALU) statuscheckand go to a flaggingroutine if it is zero: Dlvlgor,

f

Ru! DiviBor through slatus check withoul chaaging conlentsE of IIREG If Zero flag a€!, jump to z€ro Diviao! hanaller

.flt btfsc

fi :-!

iu L-' I r'l

goto

sTArus,

z

DivisiorByz€ro

To check a 16-bit value, you can OR the two bytes tosetherandseeif the resultis zero: novf ionrf btfsc golo

Diviso!,

w

DiviBor + 1. STATUS, Z DiviaionByzero

r T'wo Byteg , = = 0 2

of

Divisor

w i If Z€ro fLag a€!, t Jull9 to Zero Divisor handler r

=+ Quotient =Remainder

Figure la-a

Division signs

Finally, you may have an application that hasto handlepositiveand negativedividendsand divisors. For thesecases,Iusethe Division SignChart shownin Figre 12-2.Before executingyour division routine, mark flagsindicatingif the dividendand divisorare positive or negative,convert the negativesto positive values,executethe divisionroutine,and,upon exit, changethe quotient and remainder to negativesif appropnate.

r-f Iu

4

Experiment 106-5quaringa NumberUsing FiniteBifferenceTheorg

i

{'*{ "6-r fil

"r".; ,-! d1 !*{

Whenyou are dataprocessing, you will discovercases whereyou needmathematicaloperationsother than multiplication and division. You might be thinking of sine functions and logaritbmic operations and shuddering at the thoughtof trying to calculatevaluesfor them in the simplePIC MCU's processor. But remember,

thesecalculationswere performed literally for centuriesbeforethe inventionof the disital "comDuter"or handheldcalculator. I have put the word computer in qtotations in the previous paragraphbecauseit was the name given to individualsthat wereresponsiblefor calculatingvalues computers.Tltese people spent literally months working througha sedesof calculationsto comeup with the answerto a problem.As you would imagine,the major problemsencounteredby doing complexmathematical operationsusinghumansincludedthe time requiredas well asthe accuracyof the final result.The seemingly simpleoperationof producingsineandcosinevalues for a book of tables for navigation wasfraught with many problems,due simply to human error, that often resulted in the lossof ships and lives.

g&l

284

l,e3 PICo llCUExoeriments fon the EviI

6enius

In order to minimize the amount of time reouired to perform calculations(and the opportunitiesfor errors), a number of different mathematical tools were developedover the years.One of the most powerful tools wasgiven the namefinite differentinl theory,it which simple operationswere analyzedto find easily recognizabledifferencesbetween calculation values. The most-often-usedexample of how finite differential theory works is the calculation of squares.Looking at squaresmay seemlike a strangeplace to start, but it will make more senseat the end of this experiment. To show how finite differential theory works,considerTable 12-1,in which I have listed different integers,their squares,and the differencesof the squaresto the valuesof the adjacentsquaresYou can seethat when I have calculatedthe differencesin the values between squares,they can be expressedsimply by adding two to the previous difference. It should be obvious that by simply knowing that the squareof zero is zero and the squareof one is one, that you can calculatethe squareof any integer quite quickly.The code that I cameup for calculating the squareof47 is namedasmDifferenceand is listedhere: "asnDiff€!€nce tl.t1€ DLfference Theory,'

-

squa!€s

u6ing

Firile

Table 12-1 Intege|5, Their Squares, and the Differenceg BetLUeen Them lnteger

Square

0lfference to Previous

Dlfference ta DlfferEnEe

0

0

N/A

N/A

1

1

1

N/A

2

4

3

2

3

9

5

2

4

16

7

2

5

25

9

2

1l

2

6 7

49

13

2

8

64

15

2

9

81

17

2

10

100

19

2

PAGE , uahlin€

rcrr EquivaL€n!

a

Cofle:

(Va1u€

// Nuriber to Starts WIth // Currents Square value rdlth 1 anal Add / / fjt att // Diff€rence l= 0) gquale for nveLuen // calculate

{ = Square

Sgua!€

Diffelence Value-

-i

//

€Iihw

+ DLff€reac€i ugflat€tl squale // calculale * 2t = Diff€lence ll Add to !h€ Diffor€Dce //

)

, rshile

(1 -=

Decr€deDt

lh€

Value

Hardhf,ale ltotes: PrC15F627l ruD.ling

Finishedf,

Loop

Forever

{ li'tHz in

LISr R=DSC rNcr,ltDE "plSf Regiat€rB

, varlables CBLOCK 0:120

o\

ra t

0 47 r hitialize value Squale + 1 Squale + 1 Diffelence 1 Diff,e!€nce

ailthrf lrovf btfsc incf atl&d trrovlw

squa!6, f + 1, Dlfferenc€ STATUS, C + 1. Differeae€ + 1, f Squar€ 2 i t Diff€r€Dce, f STATIIS, C * 1, Difference value, t t t IJooD

w

varielclea

Inc:aeage W 2

5

q

p, to

z

g

3 c o

Diff€r6nc6

Ft

f Decrdr€nt qounter

th€

value

Finisheal,

IJoot)

Siaulator

eDtl

627a. inctr

!, h

F'

i RaturD Her€ until == 0 , lvalue! i Atldl "Dif,feronce" i 'rgquar6'r to get i ita nelr valu€

t uyk€ Prealko 04.04.14

O

Difference

Diff,er€nce,

gtoto at

n F. 3 o p

CN

movf,

aiLlwf btfsc incf decfaz

o

I

LooD !

Counter

1)t //

lrovlw rrovwf clrf clrf clrf niovlw novwf

x

ts

thia

Valu€ = {? Square = 0t = !, Differeace while

of

t

-

VaIu6, Square:2 Dif,f,er€ac€r2 ENDC

olg usiag Eitrit€ Diffeleace Theory, Plogram findls the gque!€ for (ririth lhe given 8 Bit hteger 16 Bit Result).

FI

In addition to squaringnumbers (finding the value of a number to the power two), finite difference theory can be usedto calculateother powe$. You may want to spenda bit of time reading about Babbage'sDffirenceEngine to tnderstand how other powers are cal-

5ectionTurelve S o l v i n g P r o g r a m m i n gP r o b l e m s

285

cos (x) = 1 x 6/6! + ...

culatedand maybeto try to comeup with an application to do it on your own.Hint:As you go to larger powers,you will discoverthat more than one differencevaluechangesfor eachnew integer. Onceyou are comfortablewith usingfinite differencetheoryfor calculatingpowersof numbe$,you can usethis knowledgeto calculatedifferentvalues.The seriesformulaslistedherewill helo: sintx/ x 7/'l|

-

x

-

y'/Jt.

-

+ x )/ 2 1 + x j / 3 ! + i

x

+ ...

/3!

r / l -

- I )

(x x

+ x a/4! -

x'/21

l x - 1 )

2 / 2 +

1J'/3

/5'-

+ ...

Experiment 107- F ind t h e Sq u a reF l o o to f a 1 6 -Bi tN u m ber are the nunber of oaldl nuibera, sum is less t'han or equal to the nulllber the square rooE is calculauea for. This is the Difference r.n

F6!

value

I canhonestlysaythat the only thing I did not understandin high schoolmathematicswashow to manually calculatesquareroots.Looking back,I suspectthat it wasdueprimarily to my poor understandingof how repeatingalgorithmsworked (I had not yet learned any programming)and secondarilytomy reluctanceto learn the materialbecauseof the V on my calculator. Unfortunatelyin mostsimplemicroprocessors and microcontrollers, no built-in squareroot instruction exists-which meansthat when I haveto implement thesefunctions,I wish I had paid more attentionin high schoolmath. When facedwith the challengeof calculatingthe squareroot of a value,I usuallyfall on what I know finite differencetheory.It canbe usedto find the squareof a value,so by reversingthe process(subtracting the differencefrom the value)and recordingthe numberof iterations,the squareroot of a numbercan be found. title lhe

"asmsqRoot 16 Bit

Eintl

th€

square

takes aalvantag€ of sguare roots that

Root

i !r-1an+

^^.1a.

= 12345r = 1t

Digitcount odd = 1,

being

of lhe Finite Program.

//

val|ue

// //

squafe Root value Difference value

Eo Square

Root

q'hi1e {

t

)

(Oald <= value) // Take Away Difference >Renainder // until valu€=value-odalt Odd=odal+2t the Diffelence // Increase - Digitcount Digitcount + 1t Square Root Val.ue // Incren€nt // elihlt

i while

(1 == 1)t

//

r Earflware Noles: PIC16F684 nrnning i

al

Finisheat,

4 vr.lz in

Loop

Forever

Sinulator

, Myke Prealko , 0{. 04,13 IJIST R=DEC I N C I J ID E " p l 6 f 5 8 4 .

inc"

r valiabLes CBLOCK 0x20 value:2

of odit:2

value"

r ThiB proglam property of t

286

2 -

reverse Squariflg

vrho,a

the

i , i i r

value the Square Root is to be founal ProceBsing variables Sguare Root of the value

ENDC

l , a 3 P I C @l l C l J E x p e r i m e n t s f o r

the Evil

Genius

PAGE r llainline

of

olg

tion operationis eliminated,makingthe application both smallerand faster. The methodshownhereworksreasonablywell,but an arguablybetter methodwould be usingNewton's methodof zerofinding.This methodis basedon the function:

sqRooE

0

lrovlw

high

novwf rlovlw movwf

+ 1 value Lorn 123{5 value

ctrf

oald + 1

novlw novwf clrf

1 oild Digitcount

Loolt: novf subwf

variable i Initialize t to have lhe Square r Root Fountl f,or it

123{5

i R€Peat Uer€ until - oaLl value , calculate i !ilot6, R€auLt Storeal i Back in nvaLuen

@at + 1, w + 1, f valu€

novf subwf, btfEa ilecf

Odat, ra' value, f, STATUS, C + 1, value

blfac golo

+ 1, value SqRootDone

movhr

2

adtlrf bEfac Lacf

dd, f gTATuS, C odd + 1, f

incf

Digitcount,

goto

Loop

sqRootDon€

f, t If MsB of nvalu€n i Value iE Negative

?

i

3

the valuea

f

t

Cio to Nunber

the

Next

sets,

oaltl

value Incremenl of Ehe Square RooE

r comlrl€teal , Einish€al, IJoop

entl

If you comparethe equivalentC codeto this assembly code,you'll noticethat thereis quite a big difference;the assemblycodecalculatesthe valueminusthe difference(Odd) andstoresthe resultin "Value" beforecheckingto seeif "Value" is negative(the most significantbit is set).The correctC equivalentcodeis: ( (value

while

( odd

= oitd

DisitCount ]

//

- odd) > 0) = valu€ Itnlil // Take Away Dif,ference // Retlaindter is Lees than zero + 2t th€ Difference // Incr€a€€ = Disitcount +1, square Root vaLue // Incren€nl

elihw

I did not note this difference in the original code, because, asI havesaid,if you are new to C programming,the ability to embedassignment statementsin conditional statementsand check their valuesis not intuitively obvious By calculating the value for "Value" insteadof doingthe compare,a full subtrac-

Section Luelve

x

ru o !-t

r".

f(x) =G' -A t rnitialize t Differ€nt

H

WhereA is the originalvalueand G is its squareroot. Whenflx) is equalto zero,it shouldbe obviousthat G is equalto the squareroot of A.To calculateG, the approximationformula:

5 CI tst

c, = t(A/G)+ G1/ 2 is used.G' (G-prime)is the next valueof G and is calculated by dividing A by its squareroot and then averaging the difference with G The formula is executed repeatedlyuntil G and G' are essentiallythe same. Table12-2showshow this formula is usedto calculate the integersquareroot of 12,345(the samevalueas the examplecode).For the initial valueof G, I usually use1/: of the valueto find the squareroot ol The closer you make the initial value of G to the actual squareroot of the number, the fewer iterations are required to find the actual squareroot, but any value other than zero canbe used. In Table12-2,you canseethat eightiterationswere neededto calculatethe squareroot of 12,345,but two issuesshouldbe noted.Fhst,althoughthis methodis quite simple,it doesrequirea divisioncapabilityin the processor, which will add to the sizeof the squareroot routine. This is not a major problem, at least not comparedto the other issue.And second,when I calculated the valuesfor G' in Table12-2,I useda calculatorand roundedup fractionalvalues.If you wereto createthis Table 12-2 NEurtons Methodfor EalculatingIntegersquare Floots G':

1

4115

2

2059

2059 '1032

3

1032

522

4

522

n3

6

r59

118

7

118

111

111

111

S o l v i n g P r o g n a m imn 9 P r o b l e m s

I

r' P

;.)

n

U2 p H

T !

159

5

,a

ftF/6t + 6l/2

6

Iteration

\t

287

applicationin assemblylanguage(or evenin C), you would haveto somehowperform this rounding operatron. Unless,of course,you usedthe floating-pointcapabilitiesof the PICC LiterMcompiler,asI havedonein csqRoot.cand csqRootN.c,which I createdquickly to testthe PIC MCU's ability to perform a squareroot with a floating-pointresult.In csqRoot.c,I usedthe built-in C sqrt function: *includle <math.h> *incluale csqRool. c - Te6t /t zunctiOa

fi

PICC Irit€

square

llyk€ prealko 05.01.19

tlouble

l"{

s tr

SquareRoot,

NsqualeRooti

main ( )

{ Nruiber = L2345.0, // EstabLiah = Nunber / 3; Nsqua!€Root // cet seetl alo

tsh€ Nunber value

{

Root

= Nsquar€Root; = (SqualeRoot + (Nunber / Squa!€RooE ) ) (Squa!€Root != Nsquar€Root ) t

SquareRoot NsquareRoot

This Drogram wiLl sinply e:<€eut€ a single square root futlctlotr to s€e holr btg it is atral how long il takes to execute.

flt

Nu!ibe!,

) while

(1 == 1),

while tnyke Drealko 05.01.19

I

//

/2t

E'rd csqRoolN

f{

aloubLe !funber,

()

nain

(

q,

Squar6Rooti

Surber - 123{5.0, // Est.lrlish the Nunber SqualeRoot = Eqlt (Nunb€r) i / / GeE j.Ea gquar€ Root !'hile

(1 == 1),

,-rl )

-**

//

Enal csqRoot

andin cSqRootNc,I cameup with a simpleimplementation of Newton'smethod:

tEd #iacludle llincludle csqRootN. c - use /* gquale Root

! :

f*"

Nelrtson. s Metboat to

Thig Drogram wiLl sinply Rool Functi.on until the the olal.

Execu!€ N€!rton,6 new valu€ is tb€

Einat

Squate same as

cSqRoot.crequired585instructionsand 37 bytesof variablememory althoughcSqRootN.crequiredonly 292instructionsand21 bytesof variablememory.This is an improvementin sizeof abouthalt The question you shouldbe askingis why isn't Newton'smethod usedin the C sqrt function?The reasonseemsto be that Newton'smethodis quite a bit slower.When I pluggedin differentvaluesto find their squareroots,I discoveredthat Newton'smethodcould take asmuch as300percentof the time that the sqrt function took. This is anotherexampleof how different code,performing the samefunction will have different operating characteristics. The standardC sqrt function takes up considerablymore spacethan Newton'smethod, but is quite a bit faster.Although I shouldnote that eventhoughit's faster,the averagecalculationtime is on the order of 7 to 9 milliseconds. In either case, the squareroot functionwill take up a substantial amountof programmemory,so its usemust be chosen judiciously.

i:**

i

l

'r{ { r I i,l

'r,*,a

288

l , e 3 P I C o l l C l JE x p e n i m e n t s f o r

the Evil

Genius

Experiment lOB-fonvertinga Bgte into

4'

Three Decimal,Tr-uoHex, or Eight Binarg R5Cll Bgtes ( i = 0 r t < 8 r i + + ) //

for

(

all

I,ooD lhrough

,t\

( (Ted[) & 0x080) != 0) Digit Iil = r 1,, ll BiE seE eLEe Digit ttl = r 0 , t

,.,",

//

Blt

ReaeE

//

shifr

in

//

Done,

].ooD Folever

TeaII) = T€4P <<

When I first introduced you to programming the PIC MCU I usedthe high-levelcapabilitiesof the C programming languageto facilitate converting numedc data to ASCII.Theseoperationsare quite easyto do in a highJevel language,but you might find it daunting to write them in assemblylanguage.It may be surprising to you to discoverthat creating thesefunctions is assemblylanguageis not very difficult and is usually quite a bit more efficient than writing them in C. The trick is recognizingthat ASCII valuesare numbersand canbe manipulatedin just the sameway as regularvaluesare manipulatedin assemblylanguage. For example,if you had a numeric value of sevenand wantedto convertit into the ASCII charactercodefor 7,you couldadd sevento the ASCII charactercodefor 0. If you had the value of sevenin the WREG, you could convert it to the ASCII character code for 7 with the sinsleinstruction:

Like in C, a character'sASCII code is substituted whenthe character,enclosedin singlequotes,is encountered. The first program,asmByte2Bin,convertsa blte valueto eightASCII bit values(1 or 0) by looping througheachbit and testingthem to seewhetheror not they are set or reset.In this program(like in the others),I sta the conversionwith the high-orderbits so they can be seeneasily in the MPLAB IDE simulator's File Register display. tit'].e

"asnlBlt€2Bin

-

Nuliber

to

"C" EguivaleDt T€rE) = Ntrmbe!,

a Eingle €ight

Save

the

==

nhile(1

1)t

Harflware Not€6: PIC16F584 ruDnins

at

4 MHz in

n

gimulator

I

l$rke Preflko 0 { . 0g , 2 9 IJIST

R=DEC

rNcrrtDE np15f 584. lnc" i variabLea cBrJocK 0x20 Diqit: 8 TdE), i E![!rc org

*"*

0

movlw

123

monwf

Tedll)

movlw

Digit

novwf

FSR

novLw novwf IJoo9: llovlw

variablea

r Nl[iber

8 i '0'

btfsc TsE), aaldLw 1 novwf INDF llf Tern9, iacf FSR, f tlecfaz i, f goto Loop

t Use n123n to i Ploglrem

Test

t FSR to Poinl t variable

to

i lvants to

trlanl

to

tsbe

nDigitn

Do 8 Bi.ta

gav€

Either

IJIJ '0'

ra Bit 7 of "Tedl!)n sets? Yea, Conv€rt WREG lo '1' flodr'0' gave the AscII Digits ghift up teateil Tenp bit Point to the Next Digit R€peet 8x

Nurlber

r Finiaheal,

Loop

For€ver

enal

Convertinga byte'svalueto hexadecimalis also quite simple due to the swapf instruction built into the PIC MCU's processor. This instructionswapsthe two

5ectionTulelve S o l v i n g P r o g r a m m i n gP r o b l e m s

|*1l

ef-3

ASCIII

Codle: //

v-"

Nev Bits

iof

//

goto This agDlicatioD conv€rls (Byte) va1u6 into 8-Bit ASCII Binary characterE.

dfr

8 Bits

if

l

r?*

289

*'1\

nybbles (high four bits and low four bits) to facilitate converting thesefour bits to a hexadecimalvalue using a subroutine.The most obvious method to convert a byte to two hexadecimalASCII charactersis to use a tableasI do in "asmByte2Hex1:" tsill€

"aatnBtt€2Hex

1 -

Nurlbet

to

aex

ASCIII

fhia aDDlicalion converEE a Eingle g-BIt (Btrt€) Value ilrto Ttdo AgCIr Il6x cberactera uaing a table. trCtr Equival€nt

U bl

sl (g

tn

HexTable \4, ,

[]

E

== 1)r

Ilaralware Notea: PrC16F58{ running

//

at

Doae,

4 lOIz in

SimulaEor

uyke Prealko 04.08.29 LIST R=DEC INCLITDE np16f 584. inctr

{u P l-{ t

r Variablea CBI.oCK 0x20 Digil:2 Ternp E![tc ors

t Nu'trbe!

variabl€s

0

l

U t,

o0 1:}

t Uae "123" i Program

movlw

123

movlrf

Terq)

awa{rf call novDrf

Terq). w HexTabl€ + 0 Digil

t Get

lrovf call novwf

Tetq), w He:.Table Digit + 1

r Get

qoto

s

r Finiahedl,

lhe

lhe

!o

trigb

l,olr

Tesl

the

lRibble

lwbble

|{

P L.

CI H 'l-{

k (U

X

r-1

analllr atLllw btfac aatallw

:fil

Loop Forov€r

.l.{

t{

A potentially more efficient method of performing this convenion is to calculatethe ASCII hex character algorithmically,replacing HexTable in the progrlam above with the following subroutine:

t1,,

{r0,,

= E€xTabl€ [ (Nuriber >> 4) & o:
whif€(1

enfl

Getlle:.:

Codle:

\9"

Digitlol Digitlll

incf PCIATE, f novwf PCL _He:rTabl€: "0123{56789A!CDEF' dt

0x00E 5 STATUS, DC 7

''' -'

Btrte2E€x: nonwf alrapf anallw aa|-llw btfac aaLlLw

T€nE) Tedp, w 0x00F 6 STATUS, IrC 7

aaltlld

.0,

movDrf incf

INDr INDF,

novf atralLw aattllw btfsc

TerD, w 0x00F 5 STAmS, DC

H€xTable:

290

Return H6r. ASCII Char for I,srwbb1e in WREG ifuEt want lower { Bitss ia th€ Ee:< Dlgit > 9?

i Yea, Move value to chalE t DigiEa

frdl

This codeteststhe valuein WREG to seeif it is greater than or equal to 0x00A, and if it is, addsthe difference betweenthe ASCII character codesfor 9 and A. Oncethis is done,the ASCII charactercodefor 0 is added to convert the numeric value to an ASCII character.To test out the operation of this subroutine,create a new program called asmByte2Hex2 and replace HexTable with GetIIex, and then test it out. In terms of efficiency,I would generally use GetFIex over HexTable becauseit can be located anlrvhere in the PIC MCU's mernorywithout concernand is short enoughthat you couldconsiderplacingit in line rather than making it a subroutine.For examplg a generalcasebyte to hex conversioncould be written as and takes about the samenumber of instructions as calling the HexTable to convert a Nybble once.

LooD Eo!€ve!

H€x ASCII Char r Return I,slwbble r for clrf PCLATH r ltr WREG ( (_Ee:(!able if & 0x100) != 0) baf PCI.ATH, O enalif ( (_EexTable if & 0x200) l= 0) bsf, PcLArH. 1 entlif if, ( (_E€xTabIe & 0x{00) != 0) baf PCLATII, 2 eDalif, andftp 0x0F want 1ow€r { bits r ilust aaltlLw Iow _HexTebL€ i Calculate the cor!€c! r offa€t gTATgS, C blfac

i r t i i

novwf incf

1 , 2 3 P I C @l ' l C UE x p e r i m e n t s f o r

INDF INDI',

f

f

the Evil

i i i i t r

Convelt Value in WREG to lwo Hex clFlact€ra at location pointeil to bV ESR Do High Nybbl€ Eirats > 9? Nybble

i t i i ; t t i t r

Yea - r,uE ln trAn to range Convert Eo ASCII Characler Save ASCII Cha:.acter Point lo t'he N€xts DeBtinalion Byte Converts the lgNt'bbL€ Do High Nybble Firsl > 9? Nybbl€

nFr

r t r i , , , i

Yes - Put in nAn to ralge Convelt to ASCII chafacte! gave ASCII Character Poiat to lhe Next D€stination Byte Retun to Caller

nFn

Genius

The GetHex subroutineis a good exampleof working with a singlenybble(four bits) and usingthe digit carry (DC) flag insteadof the standardcarryflag. The lastprogramthat I am goingto presentfor this experimentis the conversionof a byte to a decimal value (asmBin2Decl.asm). To find the hundredsand tensdigits,I repeatedlytake awayvalues(divisionby repeatedsubtraction)and add the quotient to the ASCII charactercodefor 0 to producethe correct characten.After taking awayhundredsand tens,the remainderis the numberof decimalonesin the number,which is simplyaddedto the ASCII character codefor 0.

This isn't a terdble methodof convertinga byte to decimal,but it could be improvedby noting that the leastsignificantdigit is the sumof the leastsignificant nibble and 16 timesthe mostsignificantnibble.The asmBin2Dec3.asrnroutine takesadvantageof this property and goesone better:insteadof adding16 timesthe high nibble,it addssix timesthe high nibble to the low nibble,and it addsthe 10{imesvalueto the high nibble.The codeitself is almosttwice the length of asmBin2Dec1,but it executesin a constant38 instructions.

ExFeriment 109- Produce the Even ParitgValuesfor a Bgte

One of the dyingtechnologiesof computerintedacing is RS-232.This serialinterfacewasone of the first methodsof connectingcomputersand peripheralsand requireda numberof differentskillsto implementsuccessfully.In123Robotks Experiments for theEvil someof the issuesregardingcreatGenlas,I discussed ing the voltagesneededfor the data transferand how systemsare connectedtogether.In this experiment,I want to look at how the error correctioncodewascreated and seehow efficientlyit canbe done. The traditionalformat for an RS-232datapacketis shownin Figure12-3.It containstwo bits after the data:thestopbit is an indicatorthat the datapacket hasbeensent,and givesthe senderand receivertime

to processthe currentbyte and preparelbr the transmissionof the next one. The secondbit, the parity bit, is usedto detect whetherany one of the tlansmittedbits wasreceivedin error.This bit, whensummedwith the total of all the previousbits will resultin either an evenor odd value. Thereare five diflerent typesof parity:mark,space, even,odd,andzero,in which a 1, 0, evensum,odd sum, andno bits (respectively)are sent.In mostmodern communications, the no parity bit is mostoften used If a due to the reliability of moderncommunications. it is most parity bit is requiredfor error detection,then often evenbecauseit is calculatedasthe sumof all the bits that havebeenreceivedin a packetand shouldbe an evenvalue(i.e.,bit 0 of the sumshouldbe zero). the most obvious The followingprogramdemonstrates way of calculatingthe evenparity bit-the valueof eachbit of a byte is summedtogether. titLe vaLue

"asmParity fo!

This aDplication for even pariuy each bit. "c'

Equivalent

Tetnp = 123' Parity

1 -

Ev€n

Calculate

Pality

a Byte" calculat€s a bt'te by

the surmiflg

Coale: //

Set

lhe

Byle

= 0t < 8r i++) //

Reaal through

each

bir

t

Figure la-3

RS-232datapacket

5ection Tuelve

( (TetnP & 1) == 1) Parity=Parity+1, Temp = Temp >> r, | / sm}rift- 1 Bil // iof if

Data ,

S o l v i n g P r o g r a m m i n gP r o b l e m s

Down

291

Parity=Parity&1.

== 1)t

while(1

Ilarakf,a!€ NoteE: PIC16F584 rurlltrq

.[J

u q, r{

*a

.a )

ffi nl

b . r'€

{l}

at

a gingl€

//

ParlIy

ia

//

Done,

Loop

{ MHz in

Bit

A B

Eolever

glmulalor

Myke Plealho 0{.04.07 LIS! R=DEC INCLITDE "D15f 58{.inc"

Figure f a-q

i Variablea CBLOCK 0:.20 TemD, i ENDC PAGE olg novlw novwf movlw movwf clrw

IJooD: btfsc atlfll\o rrf fl€cf,az goto

a bit of experimentation comesin handy.Remember that a binary adderconsistsof an XOR gateand an AND gate(seeFigure12-4)in which the sum (S) bit is the XOR result of the inputs. So if we want to add two valuestogetherandget the single-bitsum,we simply requirean XOR gate.

0 123 T€[ut 8 i

TerE,, 1 T€sl!), i, f Loop

0

,

hilialize

i i

Use WREG a6 Palj.ty Coutrter

VallabL€s

i Lootr> Ilele for Each t LSB of, Value S€t?

Bit

f t R€p6aE for

andlw

1

r Only

goto

S

i

eacb

IJSB iE

Finigbeal,

bit

Parity

Haff adder

Bil

Iroop Forever

enfl

This methodworks acceptablywell,but is another casewherea bit of knowledgeor binary numbersand

In asmParity2.asm,this function of the half adderis exploited (along with shifting bits) to produce a parity bit in the samenumber of instructions,executingin one-sevenththe numberof instructionsand usingone lessfile register variable than the original. Despite improving how the parity calculation softwareworks,asa tool,it's pretty limited.Theparity bit will detectonly onebit in error in the packet.With two bits,the parity bit will indicatethe data is correct. Additionally,when an error is detected,the incorrect bit is not indicated,nor is there any correctioninformation included.Thesefunctions are critical features of modern error detection/coffectcodes(ECC) used in high-speedcommunicationsand peripheral interfacins.

?

,

Experiment ll0-5ort a List of l0 Eight-BitValues Usingthe Bubble-Sort Fllgorithm

# +-'

After the time and effort spent in Section4 describing different waysto implement a bubble sort in C, you may be hopingthat I won't havea lot to sayaboutcreatinga sort in assemblylanguage. You'll be happyto hear this is true:Theassembly-language bubblesort (shown as follows) is a quite simple and faithful translation of the C languagealgorithm

{,

tr H

!d!". a-6

laq

292

l , e 3 P I C @l l C U E x p e n i m e n t s f o r

the EviI

6enius

,'aanbsort

lit].e

t ThiB program Sort 10 values t

1 -

ua€s

"Cn Equivalent

r for r

(i = 0r SoltliBt

solt

!h€

10 8-Blt

Bubble

sort

gotso

valu€5" Algorlthm

INDF,

tlecf addwf

FSR. f INDF, f

FsR, incf outsaitlel,oop_skiD

i < 10r i++) = Reaflvaluei [i] // R€ad in lhe

Een Byte

, i t

f,

i ELrats = Eirat r - Filat)

Heldwa!€ Notea: PIC15F584 rururiag

t Finisheal,

I

t ats th€

4

uHz

ia

+ (Seconal tl,

Increlrents

i, rtr goltl,iat

Enal of

novf aaLllw aubwf btfss

ESR, rt STATUS, Z

golo tlecfEz goto

OutELtl€IJoop i, f InsialelJoop

t Don€ 9x?

goto

$

; fo!€ve!

r Return Gelvalue3 at

ffi ld

-

f,

i t

llfr

,

sortlJt8t [j + 1l Seco al = g€confl (secoaal - EiIEE)

H

'jn

VaLueg

, f o r ( l = 0 r i < 9 i i + + ) // Outaial€ Sort LooP , f or (j = 0, J < (9 - i ) t j++) i l/ IttBiale Sorl LooP t (SorEr,iBt [i] > SortLial if ti + 1l) t // l|ave to SrtraD valuea r { + 11, T€mD = Sorll,islli r gortli8t r [i + 1l = Sortl,ist [i] = l[edl!), SoltlJist t lil

; t

subwf

to

Coale 3

Outsial€loop_skip

the

VaLue

for

lDtlex Liat?

at

bh€ rJiats?

tbe

End of

LooD

- Done

the

"i"

€

( (_Gelvalue & 0x0100) != 0) baf PCIJAIIH, 0 edttif ( (_cetsvaIue & 0x0200) l= 0) if PCIATII, 1 baf, enflif ( (_cetvalue if & 0x0{00) != 0) PCIATII, 2 baf, entlif aalallw 10$ _GetvaLu€ r GeE Offsets in 255 i AaLlr€aa Block btfac STATUS, C Pcr,alrfl, 0 incf mon$f, PCI. the ilumD inlo r Pelform r the Ta51e Getvalue: 10, 100, {, 15, 75, 150, 47, 2, 25O, ilr 475

!8ike

Prealko

r 0{.0{.05 IIST R=DEC rNctnDE np15f 58rl.incn , valiabl€s CBLOCK 0x20 Sortl.iBt | 10

; IJist Sort€dI

of

valu€s

!o

be

ENDC PAGE , Mainline

orlt

of

Bubbl€

Sort

- I"bfk€

I t t

(*;

tf,

a \ r

s

0 enal

clrf novlw novwf loaalloop: novf ca].l movwf incf, incf movf sublw btfsa goto

i

by loaaling i Starl , SortsLial , Setup FSR f,or IDdir€ct t Aaltlreaaingl

gortT,ist

I'd like to note a couple of discussionpoints. If you code,you'llsee work throughthe assemblyJanguage that it is essentiallya straight translation from the C languageprototype with one difference.When I coded the application, I discoveredthat when subtracting the current array value from the next, I could use the value in the WREG (Sortlist[i + 1] - Sortlist[i]) to simplify swappingthe data between the two array elements.

ESR r Retsurn H€re UntiL Loaaledl r Valuea i, w qelvalu€ INDF FSR, f i, f i, rt 10 STATUS. Z Loaalloop

movlw 9 novwf i IDsiflel.ooD ! tlovlro Sortlisl

r t i i

"i' cets the valu€ for gave ia LLat Point to Nexts EIemenC rncrenent counte!

SorEr,iatli t !Io,

Do n€xE

t Wants to

aubwf

INDF,

blf,Bc

STATI'S,

looD

one Thlough

tso tsh€ start i Poiat t th€ Liat i Use FSR as Inal€x

FSR movwf out a ial€LooD : rNDF, w novf FSR, f incf w C

aLl

t i r r i r

Point to the Next El€[l€nt + 1l sortlJiststj sortlJists Ijl If cerry Re6€1, sortl.ist Ii I >

9x

of

lJiat

+ 1l'

= SoruJiststi + 11 = sortlJiat [i + 1l + 1l - Soltti8tlil - gortliaEli + 1l + 1l + SoltIJiEt = sorrlLBr Iil

- $REG - (Sorllist -

tv

w L'

F fn

ti

] Solll,iststi

\34

lil

H

Similarly,with Sortlist[i], the value in Sortlist[i + 1] couldbe substitutedinto it by simpleaddition: sorrl,tatsf1l,

t9 {

9-.r

ginulaEo!

if

i r

'-t

= SortliBt[il + WREC = sortlistlil + (sortr,Lstli Sort'I.isl tiI ) = Sortlistli + 1l

5ectionTuelve S o l v i n g P r o g n a m m i n gP r o b l e m s

+ 1l -

293

fr

s "*.4 1.4 rft

.3J

3.,; ai

Thisoptimizationallowsfor swappingthe contents of the two array elementsin four instructions.When I originallywrote the code,I used10instructionsto swapthe valuesin the elementsusingtranslatedC code. Yearsagoon the PICList,the questioncameup regardingthe bestway to sort a short array.My immediateresponsewasto comeup with a loopingbubblesort routine like the one above.Somebodvcameun with a simplemacrothatembodiedlh..orpu,. und swapcodetogetherand createda simplebubble-sort program,which ran througheverypossiblecompare and swap,asI havedone in "asmbSort2.asm,,, which usesthe "CompareAndSwitch"macro: conpare.Bnalswilch locat CASship novf, Firstvalue, sub\of btfsc

=f:

geconalvalu€, STATUS. C

rnaclo

Firstvalue,

Secondvalue

i Is g€condvalue Value?

w

> Eilst

w ; If Carry Secontl >=

Set. then Firsts

gotso CASSkip r WREG = Seconalvatue - Eitstvalu€ = ELrEtsva1ue aaldkrf Firstvalue, f t FirstvaLue + (WREC) = sulndf Secontlvalue, f i Seconalvalue - (WREG) Seconalvalue cASSkip: €ndm

The secondprogramruns somewhatfasterthan the originalandis goodasa demonstrationtool for the squaredorder of operationsof the algorithm.For an arrayof two elements,one compare/swap is required; for threeelementqthreecompares/swaps are required; for four elements,six compares/swaps are required; and for five elements,10compare/swaps are required. Unfortunately,the numberof instructionsrequiredby this methodsoonbecomesthe limiting factorin its adoptionin usingit. For sortinga maximumof threeor four elements,this couldbe a very efficientbubble-sort method,but its usefulness diminishesaslarAerarravs mustbe sorted.

,': {Ji

Experiment111-Encrgpt and Decrgptan FSCIIZString Using a Simple SubstitutionFlgorithm

.t; t*{ :"el

traamEdcrypt

titLe Decrtzpt

;-!

anal ASCII

i l

1 - Ulrke Stringn

-

Encr!'p!

alal

Thia aDDlicalion coaverta a String of Characters sloleal ia th€ Eile Reglsters anal then al€cr]Dtss lh€sr using a glannetrical (Ror13). convelEioa table

?,r!

rrcr' Equivalent

!

Codt€:

DataSt,ring

Data encryptionis a fascinatingtopic and a numberof programsare availablefor the PIC microcontroller that implement data encryption standard (DES) and other modernencryptionalgorithms.Simplesubstitution algorithmscanbe implementedsurprisinglyeasily in PIC MCU assemblylanguage,asI will showin this experiment. iii

.r*

& ,tt

The basicoperationof a substitutionencryption algodthmis that one characteris substitutedfor anotherfrom a tablein which the charactersubstitutrons are symmetricql When the substitutedcharacter is placedbackin the table,then the originalcharacter is returned.Thisoperationis demonstratedin the following application:

!34

for

(i

= 0,

i

< at!1ea(Datastllng) t i++) / I E^ctyT,E th€ String = Encrt pt (Darastring Datastring[i] til ),

for

(i

= 0r

i

(Datagrrins) r i++) // DecrlT,t th€ Slring = Eacrypt (Datastlins Ii1 ) t

< srrlen

Datastlinslil ( 1 == 1)t

!.hil€

//

Harahtra!€ Notes: PIC15E68{ ruDning

at

Done,

4 ltlz

in

IJoop Eoreve!

Simulatsor

r.lyk€ Pledko 04.0{.05 LIST

R=DEC

tui f!

r .'r 294

l , E 3 P I C @l l C l JE x p e r i m e n t s f o r

the Evil

6enius

INCUTDE "D15f68{.

enalif aaltllw btfBc incf monwf,

inc"

i Variables CBI,OCK 0x20 DataString:12 ENDC

TIITKEPREDKOtr,

.It

novhc movDrf Inj'tIJoo9: incf

of

EncryDtioa

0 -

Datastling

1

r getup FSR lo ; tlre Datastring

Poj.nt

tv

O

UPPERCASE ' EETIE}I charectser i ascrr PCLAIIH clrf , getsuP PCLIITE for r Ta51e R€aal ( (_Encrl,I)t' if & 0x0100) != 0) bsf PCLAAA, 0 eadif

f

PoLnt

,

lo

lh€

i

novl,w

Dat.agtring

t Now, EncttE i string

rnovwf FsR lldcfl.!)t Iroop : novf INDE,

w

the i sto!€ t At Enal of

i t t t t r t r r

call Or'Wf

Eucrtz9t INDF

incf

FSR,

movf

INDF,

btfBa goto

z STllrUs, Eacrtz9tlJooD

novllr

Dataslring

f w

novwf FsR Decrl.9tlJoop : movf MDF,

€€ts rnalex

Nenl

Inlo

charac!€r gEling?

l

i i t t t r r

w

r ReD€at , gtring?

novwf

IND!

incf,

FSR,

movf

INDS'

btfaa goto

SfaTUS, z D€crylrtlooD

goto

I

f

the

to Gel charact€! Encrypt llo the sylln€tlical Decrygt Put back lh€ EncrlTrtedl Character Poinl to the N€xt

\t

Encril'l

the

to Get chalacts€r Encryl)l llo th€ Encryptsi.otr Itt back lhe Encryplefl Charecter Point to th€ Nex! Charac!€r Regeal to End of Slring?

, Now, D6cri'pl , StrLlg

call

string

to

r Finiaheal,

Enal of

Loop

t Subroutides

bEf

( (_Ercr!,Dt & b6f PCIATH, eualif ( (_EacryDr if & bEf PCLATH, enall.f ( (_Encr!'Dl if & bgf PCIJATII,

0x0100) O

r setup i TabLe l= 0)

0x0200) 1

l= 0)

0x0{00) 2

I = 0)

PcIJAlrIl Reaal

for

qv

,-t

PCI,AIIH,

1

enalif if ( (_Encrl.pt & 0x0400) != 0) bsf PCIATH, 2 endlif adtllw adaLw btfsc incf movwf _thcfy9t: alt

(0 -

r 9--!

\A')

_Efct:zpt

i i

w

Zelo Baa€ the charactera

sTATuS. C PCITATE, f PC! trNoPQRsruwqxYzABcDEEGlrriIK!!,l"

g I tRct'!13

eaal

(character

Character else Character

rrl 5.{

This applicationfirst loadsan arraybuilt with 11 file registerswith the stringof uppercasecharactersto encryptanddecrypt.Thecode,which is representedas "C" Equivathe Datastringinitializationin the header lent Code,is the standardmethodfor initializingan ASCIIZ-stringvariablearray.Using the ASCIIZ format,the lengthof the stringcanbe ignored;it is simply readuntil a byte with the valuezero is encountered. This feature minimizes the number of file registers requiredto initialize,read,and write aray elements. Next,eachcharacteris passedto a subroutinethat finds the characteroffset to the characterrelative to A, and the character in the Encrypt table at this offset is returned. The characterretumed from the Encrypt table is in the ROT 13 format in which A is changedto \ B is changedto O, and so on.This is a very basicand popularsubstitutionalgorithmusedmostlyfor demonstrationpurposes. wasgivento a high schoolstudent This assignment who cameup with the following algorithmicversionof the Encryptsubroutine: if

PCLATH

f.r.

(( Encr,lT)ts& 0x0200) != 0)

if FSR,

Dalaslringl FSR, it hitstring INDF 0 STATug, Z IaitsIJoop

if

!o

FsR

novhr aubwf call NOVWf io!1w btfss goto

clrf

X

l'rt

Lt

PAGE r ltainline org

14

_Inilstring STAfrus. C PCLATB, f PCL

>= 'N') // cha:.ectser ld-Z, change to A-u = Charaqler A-U, Change to N-Z // Chalacler - rA')' = charact€r + (\!I'

This code either subtractsor addsthe difference betweenthe ASCII charactercodefor N and the ASCII charactercodefor A. You are probablyaware that the difference between the two is 13 (assuming

1 6

K Ld4

ffi

q

t&

{ d |d

a.4 e?'{ r.&

*3

&*

r-&' t-d

Fr. !n lr.{

SectionTurelve

S o l v i n g P n o g r a m imn g P r o b l e m s

295

that thereare 26lettersin the alphabetand the break is halfwaythroughthe alphabet).But by keyingin the differenceasan arithmeticstatementthat the compiler/assembler hasto processmakesit easierto see what'shappeningand minimizesthe chancefor keying the wrongvalueor changingit inadvertently. It isn't difficult to convertto PIC MCU assembler, but the codeis somewhatcumbersome. not to mention quite hard to follow.In the followingcode,I haveindicatedthe valuewithin WREG to make the oDeration of the functioneasierto follow: Erlcrypt: sublw btfsc goto

\ ltl' STATUS, C

, WREG = rM, - WREG r Skip if Carry Re6et , (WBEG> rM') r Carry Se!, WREG is

ROTl3TJess 'M'

subht

-

('N'

-

'a')

goto ROTl3Done ROTl3LeEa: 'M'

sublw

+ ('N'

r $ I R E G- \ M ' - ( ' N ' . rA,) _ (.r{, - I,IREG) r W R E G= W R E G - ( ' N , , -'A' ) t WREG <= \r!1',

-

\A')

ROT13Done:

t W R E G= . rA,) _ t W R E G= i -'A'' r WREG =

Aalal

'M' + ('N' (.M, - WREG) W R E G+ ( r N '

Nuniber

Bublw

Nuniber

r r t r t

WREG = Number WREG WREG = Iilunber - WREG) (I{Enb€r $IREG = WREG

So by usingthe sublwinstructiona secondtime,the valuefi'om which the WREG wasoriginallysubtracted canbe removed.and the valuein WREG canbe changedfrom a negaliveto a posilive. Insteadofjust leavingthe codeasis,I decidedto spenda few minutesand seeif I couldsimplifythe conversionprocessby eliminatingthe two pathsand looking for a valueto add to the subtractionresultin WREG The subroutineI cameup with follows: Encrlrpt:

the r Elrcrl.l't r UPPERCASE ASCII

sublw

'N'

btfac addlw

STATUS. C -2 * (.N, -

sublw

'a'

296

r Carry Reset t > \M' .a')

subfw addtw

'N, -2 *

sublw

'A,

(rN'

-

\A')

if

$IREG

, carry Se!, , Doi\'n rN' -

lrove ro .A' Values

r Retsurn

Eneoaledl

the

r r r t t t , ' , t t

WREG = r!I, - WREG W R E G= - 2 , N . + 2 , A , + ( . N , - W R E q ) W R E G= - ' N ' + 2 ' A ' $IREG $IREG = rA' - (-'N' + 2 'A' - WREG) WREG= \A' + lN' + WREG 2'A' !\IREG = WREG + ('N' - '4' )

For the casein whichWREG contains'N'to'2,' the codeis asfollows: sublw sublw

\N, \A'

ROT13 (VIREG)t

Interesting,if the sublwis executedtwice,you end up with the originalvalue: Bublw

I replacedthe originalEncrypt subroutinein the asmEncryptl.c routine,with the new versionabove and calledthe applicationasmEncrypt2.c.Thiscode, althoughobviouslyvery efficient,is hard to follow and understand.Thebestway to examinewhat is happening is to considereachcasein which WREG contains a valuefrom A to'M' or a valuefrom'N' to'2.' For a valuebetweenA and'M,' the codeexecutesas follows:

WREG = r!r' - WREG , t IIREG = \At - ( 'N' r ViIREG) i IIREG = WREG + 'A' t WREG = !"REG t 'A' )

{'N'

-

If you comparethe two methodsof computingthe ROT13value,you'll seethat the resultsare the same.I don't think I would get a lot of argumentthat the second versionis more efficientat computingthe ROT13 value,althoughit is not obvioushow I derivedit. I would like to saythat I havea simpleprocessfor coming up with this type of optimization,but I mustconfessthat eachcaseis different.To comeup with the optimizationfor the ROT13 Encrypt function,I stafiedwith the desiredend points (the final valueof WREG whenthe contentsof WREG are lessthan or equalto 'M' and whenthey are greaterthan 'M'). Next,I went to my teststate(the sublw'N' instruction) andworked at finding an addlwinstructionthat would negatethe'N' throughA operation. Pleasedo not assumethat optimizationsare beyond your graspor that they cometo me becauseI have more experienceprogrammingand working with the PIC MCU than you do.In explainingthe operationof the instructionsof optimizedcode,I havepedantically listedthe registercontents,listingtheir valueasI algebraicallysimplily them.If you follow this methodology, you will find that you too will comeup with very efficient codethat meetsvour requirements.

l , a 3 P I C o l l C U E x p e n i m e n t sf o r

the EviI

Genius

tql

112-Eeneratea FibonacciNumberSequence X Experiment rd

o

Eight hundredyearsago,the Italian konardo Pisano Fibonaccilooked at the problemof how rabbitsreproducedand how the growthof their populationcould be plotted.Postulatingthat rabbitscouldproducea litter oncea month,after they weretwo monthsold, Fibonacci cameup with a sequenceof numbers that is the baneof computersciencestudentsmore than three-quartersof a millenniumlater. Startingwith onepair of new born rabbits,the population of rabbitsin the first year canbe listedas: L,

This sequenceis normallydescribedasthe resultof a recursivefitnction As I mentioned previously,recursive functions perform part of a specified operation and then call themselves to completethe operation.I discouragethe useof recursivefunctions in PIC MCU programming(of all types,not just assemblyor C) becauseof the lack of an arbitrary-lengthprogram counterstack. Without the possibilityof recursion,the problem becomesquite simple,with eachvaluein the sequence beingdefinedby the statement: = Eibti

"asmribonacci titte 24 TermE" Sequence for

the

cleat€

15 bil wolhLng with i D€noastrate lhe Nunb€r Arraya to calculate i for 2{ E€rms. Fibonacci E€riea ; t

"C"

tinl , ,

EquivaLenl

Coale:

Fibt241;

Fiblol

= Fibtll

//

Sequenc€

49 Byle-Fibonacci

//

].t Eirat

Two Valuea

-

1l

+ Fibti

-

2I

that can be checkedby applyingit to the sequenceof the previousnumbers, The requirement for this application is to produce the Fibonacci rabbit population growth valuesfor two years.Looking at the examplesequenceabove,you canseethat the valueof the thirteenthmonth will be approaching255,which meansthat in order to store the populationvalues,you will haveto use16-bitvariables.The general form of the addition is: . .

Add high bytes Add low bytes

.

If low-byte sumis greaterthan 255 (carry bit set),incrementthe high-bytesum

(1 == alt

//

i llaralware Not€a: PIC15E584 rutraing ;

Finisbeal'

at

{ uEz

$

ts

I F

r

x 0,

IJoop For€ver

in

3 o

|-...

, for (L = 2i i < 24t i++) - 21t - 1l + Eistt = Fibli Fiblil r / / cet Each value , r whl.l€

f-r.

;fl

1

are

rt

H l\)

Elbanacci

1 3 , 2 1 - ,3 4 , 5 5 , 4 9 , L 4 4

t-,2,3,5,8,

Fibtil

In my solution,I havesetup a 24-element,16-bit array,in which eachmonth's element value is stored and usedto produce the value for later elements.The solution to the problem usesthe FSR index pointer register to keep track of which element (and which To byte of the element) is currently being accessed. changethe FSR,I useincf and decf (incrementand decrementinstructions,respectively),and I add explicit valuesto the FSR.

SimulaEor

o o

i , !,l].ke P!€ilko ,04.08.31

}l. LIST R=DEC INCL(rDE'915f

584. inc'

, variableE cBrJocK 0x20 Erbr2*24 i,

Sloring t Array values i Fibonacci

TerD:2 ENDC PAGE org

0

c l r f

E l b + ( 0 r 2 ) + 1

clrf mov].w movwf mo'\tttf,

Fib+ (1 *2)+1 1 Fib + (0 * 2) Fib + (1 * 2)

t Inltlalize t Two A.rray

5ectionTurelve S o l v i n g P r o g n a nmi n g P r o b l e m s

1El El€dlenta

z s 5

tt (D ry V2

o

to .a

o o o

297

ql f.t

(u

.a ts r..l

x F

f-1 r{-{

novlw

2A - 2

movlrf

i

novlw

Fib

novrdf IrooD ! alecf mov! movwf tl6cf movf movwf alecf movf

lilumber of Eldlents to

+ (2 * 2)

t Point t Start

r*{

"}J

ASR. MDE, T€a\D ESR, INDF, E€[rI, FSR, INDF,

- 1l , Point ro Fibti i anal Save in Tettp

f w + L f

I,J

.r{

fr"{ & I

aatalwf movf movwf Lncf &ovf novwf incf

FSR, Tetnp, MDF FSR, TqE IIIDF FSR,

alecf,sz goto

i, f lJoop I

= 0x03DB (ln ReverseByteOrder) Figure la-5

f w

r Aatdl Fibli t Telqt

-

2l

Fibonaccivalue

to

T€aI) + 1, f FsR, f INDF, rt Tetnp, f sTtTUs, c Tetry + 1, f

atldlrf tlecf novf aalabrf btsfEc incf

goto

6n

to the of tbe Arlay

FSR

In Figure 12-5,I havecircledthe sixteenthelement of the Fib array.The element'sfirst addressin the zerobasedFib arrayis found usingthe formula: i Store r Fibtil

!s{

AiLI

TerE) in

Address = Array (Elenent - 1)l

f

SEa-rL Address

r

12 x

w f + 1,

w

f ,

Repeat

i

Finiaheal,

(24 -

2)x

trooD

€ndl

When you run this application,one of the biggest problemsyou will encounteris trying to determine whetheror not the answersare correct.Lookins at the File Registerwindowin MPLAB-IDE (seeFigure l25), you may havea difficult time pickingout the highervaluesand translatingthem into their decimal eouivalent.

So,to find the first byte of the sixteenthelement,the first addressis 0x03E(assumingFib startsat file register address0x020).This value is savedin Little Endian format (low byte at low address,high byte at high address),and the valueis 0x03DB-even thoughit lookslike 0x0DB03.Convertingto decimal,this value is 987(whichwasfound by evaluatingthe expression[3 x 256] + [13x 16] + 11),exactlywhat is expected. I'm goingthroughthis calculationbecause, like C pointer values,MPLAB IDE doesnot showthe contentsof an array (especiallywith elernentsthat are 16 bits and greater),and to seewhat they are,you will haveto employa bit of ingenuity.For the mostpart,I recommendyou avoiddata structureswith operating valuesthat requirethis amountof work to understand, but in somecasescalculatingan addressand convertins the valuemanuallvcannotbe avoided.

rr] r"{

Experiment 113-Findthe LargestEommonFactor of Tr.uoEieht-BitNumbers

F-l

c) g

To round out the section,Iwant to leaveyou with an application that can be expressedreasonablycrisply in the C language.However, translating the function to assemblycanhavea numberof uniquechallengesthat will needto be addressed. Finding the largestcommon factor of two eight-bit numbers is very difficult when translatingbetweenthe two programminglanguages directly.Substitutingdirect translationsof the C assembly languagestatementswould havepotentiallymade

".1

t"{

q, g{

X td 298

l , e 3 P I C @f l C l JE x p e r i m e n t s f o n t h e E v i I

Genius

the application more difficult to write and executeefficiently. The task of finding the largest common factor of two numbersis not particularlydifficult,althoughit requires a number of steps.The ftst is to find all the factors of each of the numbers.This is done by repeatedly dividing eachvaluewith incrementingdivisors until a divisorthat producesa remainderof zero is found. When the remainder of zero is found, the quotient of the value and the divisor (which is a factor of the value)must be savedasthe new valueand the processrepeatedto find other factors.In highJevel languageprogramming,this is quite easyto do,but in programming,codingthe division assembly-language routine requiresextrawork. However,this extrawork canmake it is possibleto perform the routine only once,simplifythe program,make it shorter,and make it executefaster. Becauseof the needfor divisionroutinesand storageof the differentfactorsof eachvalue,I usedtwo uniquevariablearraysthat are indexedusingcounters. Using a high-levellanguage, this is easyto accomplish, but in the mid-rangePIC MCU, it is more difficult becauseonly one indexregisteris availableand becausethe addressfor eachvalueneedsto be recalculated.Tosimplilf workingwith the index registerwith multiple arrayqsomeplanningis required-planning to make surethat the index you are both readhg from andwriting to is the lastindex accessed so multiple recalculationsare not required.

t

i = 2 r i - L i ((1 != value) while && (valu€ // Final the Factors if

llaralware Noles: PIC15F58{ running et { MEz in Resel is tied tlirectly !o vcc PulLup/ Progra.lring Haralware

int int lnt int

//

,

5ectionTurelve

r+

== 0

}J

s tJ

Proce€s of

trin

I Save?

3::l F"r.

Faclor

enal GetFactota

nain( )

(

int

i,

Jt

rt

= 195t = 22{t

Nunber1 Nurbe!2

v

(llulrbell, FacEorlliat) // Get FactorB GetFactors(lilurber2, raclor2Lists) cetl'actols

t

ftl

i

r

= 1t IJargeslFactor lJargeEt Factor // CaLculat€ (i - 1, (i < 15) && (0 != Faclorll,ist for i++) for (j = 1r (j < 15) && (0 != Factsorllist tiI ); j ++) (Factsorll"ist til == Facto!2]Ji8ttjl if ) // Ha''e a colEron Factsor | * = LargestFactor LalgeatFactor Factorllist IiI t = Faclo!2l.isl racto!1liEt Ij I =0t [il // fi ,

lbe

simulatsor via

N\rnib6r1, lirufiber2 t Eactorlliat [15] t Eactor2r,l.at I16l t large6!!actort

o

H

lthile

Iil!'ke Pr€flko 0{.09.01

Faclo!

// fi' l i++, // !,ook at Nexl vaLue // elihw ] (1 l= value) if to // RemaiDing Prille = value; Factorr,ial [jl ia Final // Re$ainate!

cdnron

Filst for two 8-bil s€l the factors nuribers adtl uae th€[l to findl the lalge5t factor. Thia is a atirect usage of cdrron rncn Equivalent' Coale' of the aEs€[lbly lansnras€ v€rsioD

Restalt

o

Fr, 5

!= i))

(0 == (vaLue % i)) o! value/i // rf Renainate! tE is a Eactor | // value=va1u€/i; // Eake Awey Factor = it FactorlislIj++l to the IJists // Add Factor //

FI X r-t

t

in the assemblyJanguagecode that cannot be representedin the C languageversionof the application.

the largeat ![t,I!be!s',

) a lillrniber

aactorliat [0] = 1t for (i = 1r i < 16r i++) tshe Faclorl,iat I / I'litlalLze = 0t FactorlJiats lil

The assernblylanguageresult for this experiment is "asmlcFactor.asm"and its operationis bestillustrated using"clCFactor.c".Obviously,many subtletiesexist

#lncluale <9ic.h> - Get cr,cBactor /* Factor of 2 8 Bit

(irlt Faclor',ist[] va1ue, int of / I FLatl AlrJ lhe Factora

cetFactora |

,

//

E^d

(1 == 1), // Finished,

til

);

t'rJ

Hr

H {

c

IrooD Eorev€!

cr,cFactor

The efficienciesof the assembly-languageversion over the C versionbecamevery apparentwhen some measurementswere taken of the two applications.The versionexecutedin one quarterof assemblyJanguage the numberof cyclesof the C version(4,800to 1.5,275 accordingto the MPLAB IDE Stopwatch) and also took up one quarterof the amountof spacetaken by the C languageversion(92 instructionsto 367instructions).The improvementin the numberof file registers

S o l v i n g P r o g n a m m i n gP n o b l e m s

T J

299

x

s

3 ff o

Ft

(f)

usedwasnot asdramatic(the assemblyJanguage versionrequires72 file registersversusthe 88 requiredfor the C languageversion).From theseparameters, you might arguethat the assembly-language versionis four timesbetter than the C languageversionand is clearly the "best" of the two. The assembly-language versionwould be the bestif speedand sizewere the criticalrequirementsfor the application.If developmentcostwasan important requirement,the C languageversionwould win, hands down.Rememberthat the designof the algorithm, which I coded in the C languagebefore attempting to write it out in assembler, hasto be donein eithercase, and if a highJevellanguageis used,the codecansubstitutefor documentation. In this case,you are not developingcodethat implementsthe samefunction twice.And, in the caseof makingchangesto the code, if the sourcecodeitself is usedasdocumentation,the documentationfor the applicationis changedautomatically.Finally,the C languageversioncanbe transferred to otherprocessors with a minimum of conversioneffort.If the applicationwascodedin assemblylanguage, it would haveto be rewrittenin the appropriateassembler. This lastpoint is known asthe portabiw of the code.By definition assemblylanguagehasvery poor portability acrossdifferentplatforms.

.

Find the eight-bitmean and median of a list of 10 numbers.

.

Producean eight-bitrandom number usingan LFSR and an eight-bitseed.

.

Use structuresto add two real numbers together.

.

Sort a list of numbersusinga bit-map.

.

Reversethe charactersin a string. Find the Y:0 crossingpoint for an equationin the format Y = Mx3 + B. Find the day of the week for a given date.

. . . .

Compressan ASCII string (i.e.,replacerepeating valueswith a singlecharacter). Implement a simpletranspositioncipher.

Along with keepinga list of possiblequestions,a quick Googlesearchfor "ProgrammingProblems"is a usefulway to find additionalquestionsto work tbrough. In July of 2004,this searchyielded over six million hits.The following selection camefrom the top of the list and offers many useful and appropriate questlons: ACM InternationalCollegiateProgramming Contest/EuropeanDivision www.acm.inf.ethz.ch/ProblemSetArchive.html o

For Eonsideration tbt

iJ . t'i

*..i ,l:

li {.ii

':*

.r* lt-: ,f1

tt f)

Teacherqmore than anybodyelse,understandthe importanceof creatingdifferentassignmentand exam problems.If a setof problems(suchasthe 10in this section)wereusedfor morethanoneyearin programming course,chancesare goodthat solutionswould becomeavailableover the Internet in time for start of the next course.Thisis unfortunatebecausethe purposeof thesequestionsis to help the studentunderstandproblemrequirements,developan algorithmfor the solution,andfinally presentthe resultaspart of the project.Themarksare really secondary. The problem:It's difficult to comeup with new questions. I find it usefulto keep a runninglog of questionsthat I think of during the year.I write down all sortsof thingsthat I comeup in my day-to-daywork. Someof the problemsin my currentlist that could havebeenconsideredfor this sectionincludethe following: .

For a set of X,Y points,find the equationfor the trend line.

.

Multiply two numberstogetherusingBoothe's alsorithm.

:"r,,

300

Varioussampleproblems American ComputerScienceLeague www.acsl.org/samples.htm High schoollevel programmingproblems Department of Mathematicsand Computer Sciences, WesternCarolina University problems.pdf www.cs.wcu.edu/cscontest/2@/zou ProgrammingProblems,15th Annual Computer ScienceProgamming Contest Problem SetArchive http://acm.uva.es/problemset/ Severalhundredproblems,advertisedasbeing typical to exan/project problems Universily of California.1999Programming Contest www.cs.berkeley.edu/-'hi lfingr/programmi ngcontest/f99-contest.pdf Somebasicprogrammingproblems

l , e 3 P I C @l l C U E x p e r i m e n t s f o r

the EviI

6enius

Sect ion Thirteen

TipZaps@Flobot (rated tols Ieast 10V)

at

47 /.rF electrolytic caPacr.to!s 0.1 pF capacitor (aoy type) 0.01 pF capacitor Radio Shack Zipzaps remote control ca!

DUM

1 ZipZaps Pe!fo!mance Booster Uplrade Kit

Breadboa!d

1 Plcr6F68 4

Solde!ing

.I

ilon

solde r

38 KHz IR TV lenote control !ece j.ve!s

RoLarY hand. tool (Dremel tool) with carbide disk cutsl a^+,r

^

r,r

MAx?55

I

I I

Tvro-J.ine, 16column LCD

1 1N5817 Schottky diode

high-speed 9/64-inch bit dlill

2 LEDs

Needle-nose

5 IR LEDS

20- to Black

pliers

24-gauge

rrile

Light-dependent resi.stors

wire

10k resi,stors

Red wire Wile-wlap Permaneot Ili!e

rrile

1k j.esistols

malkel

4.7k lesistors 470f,) lesistols

clippels

Breadboard

100O lesistols

Wiling

10k breadboa!dmountable potent iometer

kit

Scisso!s Xrazy Glue Five-minute

100 pF electrolytic capaci-

epoxy

Over the yearg I have gotten at least two dozen emails from people who want to come up 'ri/iththeir own copiesof establishedproducts becausewhat's already out there is so expensiveand they feel they could produceproducts at a fraction of the establishedproduct's

14-pin, machined pin DtP socket Tvro-piD, tightangrle stlaightthlough connecto! rightFour-pin, angle straightth!ougtr coanecto! Tero-pin, straightsocket thlough Four-pj.n, straight-throu9h socket Prototyping

PCB

Breadboardmountable SPDT switch (E-Slritch EGl903 Recormeoded) Breadboardnountable mcrnentaly On push button sfin heat-sh!ink tubing Thlee-cell AA battety pack AA al,kaline batte!ies 6-32, nylon

2-inch bolts

5-32 oylon

long nuts

price. My only experienceswith retail products are with the Tab Electronics Build Your Own Robot Kit and the Tab Electronics Sumo-Bot Kit, and they have beeneye-openingexperiences. In comingup with theseproductqwe agonizedover featuresand partsto

301

try and meetthe requiled pricepoint. I very quickly learnedthat the productcostshouldideallybe onesixth,and no more than one-fifthof the retail price. The costdifferentialis due to shipping,warehousing, packaging,advertising, warranty,nonrecurring expenses costs,and profits for both the manulacturer and retailer.Using this rule of thumb,I am amazed that Radio Shackcan sellthe ZipZapsorremote-control carsfor $20.00. The ZipZapsremote-controlcarsare a lot of fun to play with. If you haven'thad the chanceto at leasttry one out in the store,you shoulddo so immediately.Figure 13-l showsthe completepackage,a car and remote-controlunit that doublesasa charger.The car hasa 1l.2V NiMH batterythat canbe chargedin about a minuteand allowsthe car to run for threeor four minutesat full speed.The car is capableof runningforward and backwardand canchangedirection;some earlierremote-controlcarscould only movelbrward and backwards, and turn in only one directionwhile in reverse.Radio Shackoffersa wide rangeof different bodiesfor the kits,alongwith variousaccessories, includingperformanceupgradesAs you play with the ZipZaps,you shouldbe impressedwith its robustness. It handlescrashinginto objectsvery well and evensurvivesthe mostextremeactivities(performingjumps, runningotTtables,and so on) without complaint.It's a pretty amazingpackagewhenyou considerthat they cost$3 to $4 to manufacture.

Fiqure l3-l The Radio ShackZipZaps@car with remotecontrol and charger

302

I am actuallysurprisedto discoverthat nobodyhas exploredthe idea of wing the ZipZaps asthe basisfor a mobilerobot chassis, whenusingother larger remote-controlcar chassisasthe basisfor robots, whichis very common.Looking at the ZipZaps,I can comeup with a few concems,namely: .

1.2-voltoperation

.

Limited operatingtime

. .

Smallsize Minimal payloadcapability

.

Surprisinglysophisticatedmotor and steering driver circuitry (and complexcircuitry overall) Ternarysteering(three states:left, right, or straight)

.

Takingolf the body,the Zipzaps is very compactly designed.Youcanpop off the circuit board'splastic coverand get a better idea of the electronicsthat act as the radio receiverandthe motor/steeringdrivers.You may haveneverseen,and haveprobablyneverworked with, the surface-mount componentsusedin the ZipZaps' electronicboard (seeFigure 13-2),which may minimizeyour confidencein modifyingthe circuitry.All theseconcernsare legitimate,and usingthe ZipZaps asthe basisfor a PIC MCU controlledmobile robot may seemunlikely,but asI will showin the experimentsthat follow,the ZipZaps is designedusing traditionalmethodologies. You can hack one into a robot over the courseof a weekendfor suryrisingly low cost. An importantaspectof hackingthe ZipZaps into a robot hasbeenthe work that hasbeenperformedin the previouschaptersand the skills and knowledge that work hasdeveloped.As I work throughthis sec-

'f3-? Figure TheZipZaps electronicsseemsmall and difficult to work with, but can be usedas a basis for a surprisinglysophisticatedrobot.

l , a 3 P I C o l ' l C UE x o e r i m e n t s f o r

the Evi I

Genius

tion, I will be addingrobot featuresto the ZipZaps chassisthat havebeenpresentedand prototypedearlier in the book;in fact much of the incrementalcode that is addedwith new featureswascut and pasted With a simdirectly from thesepreviousexperiments. ple basestructurefor the software,usingthe establishedcodebaseI wasableto createa very set of robot functionsfor the ZrpZapsrn sophisticated just a few days. I really had a lot of fun working throughthe experimentsin this chapterand I think you will too.But beforeyou start cuttingrp a Zrpzaps for your own robot, I suggestthat you spendsometime reading

throughthis sectionand rereading(and redoing)the and presentedthe variousexperimentsthat discussed control,software,and interfacefeaturesrequiredfor the robot.You may not be ableto find all the partsI used(althoughthey are pretty generic)or, due to you may find that they work difassemblydifferences, ferentlyor haveto be tuned in a differentway.By readingthroughthe sectionfirst and makingsureyou understandhow everythingis supposedto work, you will minimizethe amountof work neededto complete iirst the robot and maximizethe chancesfor success on timeat everystep.Havinga differentperspeclive the robot,you will likely comeup with somethingeven better than what'spresentedhere!

- Char acterizing the ZipZaps Experiment 1I t-.1 Tool

Box

Radio Shack ZipZaps lemote-control ca!

DMM

ZipZaps Booster

Soldering

Pe!formance Upgrade Kit

Needle-nose pliers

20- to

Before we canstart designingrobot hardwarefor a Zrpzaps remote-controlcar,it's important to underof the motor driversand the standthe characteristics informationthat we want to steeringactuators.The collectincludeswhich circuitsare usedto ddve the motorsandthe steering,what voltageis appliedto them,and how muchcurrentthey consumeduring operation.Todo this,you will haveto probe the ZipZapsvery carefully,asyou will be desolderingand resolderingsomewires.This is somewhatfine work, and you may want to take my resultson faith. Although you will be doingsimilarwork in the next now is a goodtime to get coupleof experiments, startedand get somepractice. I want you to know Justasa note of reassurance, that duringthis step(and the following steps),I broke a numberof wiresfrom the car chassisto the PCB.I wasableto reattachthem,andthe ZipZapsran fine afterward. The first order of businesswasto solderon 2- to 3inch lengthsof wire onto the red wire and black wire connectionsof the PCB.It is difficult to showin a photographwhat wasdone becauseI attachedthe wire to the backsideof the PCB (assumingthat the sidethat hasthe wires,shownin Figure13-3,is calledthe front).

iron

So lde r 24-gauge wire

Thesewireswill be requiredfor the next experiment. While holdingthe driving wheelsof the ZrpZapsoff the table (no load condition)and with the wheels stalledagainsta tabletop (worstcasewith the motor essentiallyshort circuited),I measuredthe voltage (whichis the batteryoutput) acrossthe two wiresas givenin Thble13-1.The minimal voltagedrop seen from nothingrunningto runningand stalledis an indicationthat the motor driversare well designedfor the motor and that the batteryhassomeexcesscapacity. Next. I wantedto look at the motor driversthemselves. With a bit of searchingwith a DMM, I wasable to infer that the motor driver circuit looks something like Figure13-4.Thisis an innovativemotor driver to us, designwith two control linesand is advantageous asI will showin the next coupleof experiments.Totest the motor driver,I first measuredthe voltageacross the motor (at the yellow and blue wires)for the conditionslistedin Table13-2.I then measuredthe current passingthroughthe motor for the sameconditionsby desolderingone of the motor wiresfuomthe PCB. WhenI wasfinished.I solderedthe Inoloru ire backon. The motor ddver shouldbe fairly easyto interface to a PIC MCU. The only problemyou shouldbe aware

5ection Thirteen Z i p Z a p s o R o b o t

303

Table 13-2 Motor Parameters Valtage FEross Mator

Cuffent

Condition No Load.Motor Running

V 1.20

25nA

Motor Stallcd

0.65V

l{10+mA

Throush Motor

Table 13-3 steering Drivef5olenoid Parameters

Figure l3-3 side"

Close-upviewof ZipZaps PCB's "front

of is the needto maintaina constantcurrentfrom the PIC MCU to the transistor's base.This will requirethe changingthe driver transistor-base currentlimit resistorto a valuethat will providethe sameamount of basecurrentaswasavailableto the transistors originally. Again, the motol driver seemsto be well designed with dre ability to handlethe currentproducedby a stalledmotorcondition. After seeingtheseresults,I decidedI wantedto usethe motor driver circuit built onto the ZipzapsPCB. Next.I wantedto characterize the stceringactuator electronics. After a few minutesol probingthe PCB,I cameup with thc circuitsltownin Figure13--5. EachoI the two solenoidcoilsof the steedngmechanismare drivenby the singlebipolarNPN transistors with the

Condition

Voltage Rcross solenoid

Current Through Solenoid

No turn

0V

omA

Turning/Solenoid Active

1.20V

60 mA

parameterslistedin Thble13-3.Like the motor driver, the steeringgearshouldeasilydrive a PIC MCU I/O pin.The currentJimitingresistanceshouldbe changed againto makesurethe sameamountof currentpasses throughthe baseof the steeringdriver transiston. While doingthis characterization, I ran into two problems.First,the PCB is smalland usessurfacemount technology(SMT) components, which are harderto rework than the pin-through-holecomponentsthat you are usedto. Patience,planning,and a small-tipsolderingiron are all that is required.Second, it wasdifficult workingwith the steeringgearsolenoid wires,asthey are extremelythin magneticwires and will pull themselves from the PCB whenyou are solderingadjacentcomponents.They can be resoldered easily,but you will haveto noticewhen they are missing,andyou will find that they canbe difficult to manipulate.

Table 13-1 BattergVoltageat DifferentDrivingMotor states trondition

Voltage

Motors.SleeringOff

I . 3 6V

MolorsRunning. No Load

1 . 3v0

StallcdMotors

1 . 2V 6

So l o noi d Coil

st\48T3906

Control (s2A) from Radio

st\,4 8T3904 (s1A)

SMBT39O6 (S2A)

Control from Radio Sl\ilBT3904 (s1A)

Control from Radio

Figufe l3-q

Mobr driver

304

l , P 3 P I C @l l C U E x p e r i m e n t s f o r

Figurel3-5

SMBT39O4

(s1A)

Steering driver

the Evil

Genius

Experiment ll5-Plf

ryl

MCUPor-uer 5upplg

h,

,TT Radio Shack Zipzaps !emote-cont!oI car

**, a-{ -*) fTr

P I C 1 6 A 6 84 MAx756 1N581? Schottky

diode

I,EDS

t! i r

10of,) resistor 100 pF electrolyt ic (lated at capacito!s Ieast l0v)

DMM Needle-oose pliers

0.1 pF capacj.tor tYpe)

Breadboa!d Wiring

kit

The f st thing I had to do in the processof gettingthe ZipZapsrcbottogether was come up with a schemeto power the PIC16F684that would control the robot. This actually tumed out to be a fairly painlessprocess, althougha coupleof operationalissuesregardingthe selectedchip andits usewith the PIC16F684had to be investigated.To summarizethe experiment'sresults, the addition of a PIC6F684power supply went very smoothly,and I learned a bit more about the PIC MCU andhad somethingsto think aboutin later robot projects like this one. If I were to look at the Zipzaps Robot from a perspectivethat otherpeoplecouldeasilyunderstand,I would note that it is poweredby a single1.2-volt rechargeable battery.If you look at the PIC16F684(or, indeed,any PIC MCU) datasheet, you will discover that the minimum voltage on which they run is 2.0 volts.For the Zipzaps robot PIC MCU to run at that speed,either I neededto add an additionalbattery or a step-uppower supply.The suggestionof addinga stepup power supplymay seemlike overkill,but adding anotherbattery had nothinggoingfor it; not only did it require spacethat was unavailablein the chassis,but the battery usedin the Zipzaps is heary (which will decreasethe performanceof the robot),and I would have to come up with a specialchargingc cuit for the two additional batteries. To go with the step-uppower supply,I had a number of requirementsthat it had to meet beforeI was comfortable using it. The requirements were: .

Noiseimmunity-I didn't want motor/steering electricalnoiseto affect the operationof the PICMCU.

*.-"&

(anY

I ,

0.0L pF capacitor

.

.

.

Smallsize-The control chip could be no larger than an eight-pinDIP, and the number of support componentshad to be very minimal. Reasonablerun time-The robot would run for a reasonableamount of time before requiring recharging. Able to survivePICkit programmingbackdriving. Backdrivingis the term usedto describe the forcing of an overvoltagecondition on a chip's output. Backdrivingtypically becomes very wastefulin terms of power and can damagesomecircuits.

ffi LI {

I

w

'L; g

Using a switchmodestep-uppower supplyeliminatesmany of theseconcerns.The capacitor filters and inductor energy storagevery effectively filters out electrical noisebetweenthe motor and the circuitrypoweredby the step-uppowersupply.There are a plethora of differentstep-uppower suppliesto choosefrom, which madethe task of choosinga small,efficient deviceeasier,althoughit still took quite a bit of time for me to settle on the Maxim MAX756. This chip is designedfor poweringelectronicsusinga single1.5V or 1.2V battery which is exactlythe situationwe have here. To validatethe operationof the MAX756 and make sure it would be appropriate for the Zipzaps robot, I built the circuit shovmin Figure13-6.Thisis a fairly standardapplicationof the MAX756, usingvaluesand componentsrecommendedby the manufacturer. The first test wasto seeiI the ZipZaps baltery could run this chip and haveit power a reasonablesizeload.The circuitin Figure13-6providesa simpleLED (requiring

5ection Thirteen Z i p Z a p s o Ro b o t

305

Elj

ht

*?"€

:x ldi-t

about 10mA) and the cFlash.capplication,which flashesan LED betweenRA4 and RA5. The application ran the first time, but did not run after that.Using my DMM,I discoveredthat the voltageoutput of the MAX756, with all its heavycapacitance,took a very long time to go below500mV-just enoughto put the PIC microcontrollerinto an invalid state.To fix this problem,I enabledthe brownoutreset circuitry in the cFlash.cprogram's configuration fuses andrenamedthe applicationZipFlash.c.Asa side note,all the programsin this sectionstartwith "Zip" for easyfinding,rather than the traditionalc or asm.If I didn't want to enablethe brownoutresetcircuitry,I could have put a bleedresistorof 4-7k or more across the PIC16F684's Vdd andVsspins,which would drain the capacitorswhen powerwasremoved. *incluale - 9irp1€ zl.pFLash.c /* an IJED on ZipZaDa, Prc15E584

c program

llhia Program ia a motllfi€dl 2. crr . witb Brolrn Ou! Delect Active RlA4 - IJED Poaitive RA5 - IJED lil€gative

F X

i

i

r---!

a q

vergiofl

to

of

FIaBh

',cFlash

Cofilection connection

royke Dr€alko 04.11.25

coNFIG ( MTIO & lvE||tDIS & PWRTEN & UCI,RI'IS IJNPROTECT \ & I'IIPRCXIECT & BOREN & IESODIS & FCMDIS) t

&

nain( )

(

PORTA = 0, Cl'lCONo = 7, ANSEIJ - 0; TRISM = 0t TRISAs = 0i

Lll

e*€

== 7l

!rhi1€(1

// // //

Turn off ComparatorB Tulr off Alc Make RA4/8A5 outsputs

ll

Loop Eorever

{ for

t'*

for

f I I

) I

(i (j

= 0r

i

< 255r i++) // Si,ryrle 500ms Delay = 0r i < L29? )++lt

RAo = RAo ^ Lt // elihw // E'l.d. zipFLash

/l

T oggle

rJED state

"}{ The applicationwasbuilt on a breadboard(seeFigure 13-7),and after enablingbrownoutrest,it ran fine and did not seemto affectthe operationof the ZipZapschassisand PCB (which,other than the addition of wiresfrom the battery'spositiveand negative connectionEwasunmodified).The batterycouldbe

306

Zipzaps

Figure 13-6 ZipZapspower supply testcircuit

chargedfrom a remotecontrol while pluggedinto the power supplycircuit.And when the batterywas charged,it not only chargedthe ZipZaps' batterybut alsopoweredthe MAX756 and the PIC16F684to which it wasconnected. With the MAX756 power supplyand PIC16F684 circuit addedto the ZipZaps chassis, I found that the PIC16F684's LED would flashfor 10 to 11 minutes (abouthalf the time the unmodifiedZipZapswould sit on the tablebeforeloosingenoughchargeto the radio receiverto stopbeingableto move).With the radio receiverand wiring still present,I found that the motor would run, without any dragon the wheelqfor about4 minutes,about the sameasthe unmodifiedZipZaps. The conclusionI reachedhereis that any task the robot is performingshouldbe completedin 2 minutes or so,to make surethat it doesnot run out of power.If you werein somekind of contest,you would haveto make surethat you won in 2 minutesor less.Otherwise you would loosefrom lack of batterypower. Essentially,all the requirements outlined here are met with the MAX756 step-uppower supply.Looking at the voltageoutput from the MAX756 usingan oscilloscope,no indicationwasgiventhat motor noisewas beingpassedto the PIC16F684.TheMAX756 is an eight-pinpart with five supportcomponents, which madeit appropriatefor usein this application.The runningtime of the robot did not seemto be negatively affectedby the additionof the MAX756, PIC16F684, and LEDs to the load poweredby the ZrpZaps rechargeablebattery The only issuenot addressedin this experimentis whetheror not the MAX756 cantoleratethe 5 volts appliedto program the PIC16F684in circuit. This is an important requirement for the application,asI will discussbelow,andit is not mentionedin the MAX756 datasheet. To be on the safeside,a silicondiodewill be usedto isolatethe PIC16F684's power supplyfrom the MAX756's output.The following experimentswill determineif this will affectthe operationof the other componentson the Robot'sPCB.

l , e 3 P I C o l ' l C UE x p e n i m e n t s f o r

the Evil

Genius

14 X i-s

Experiment 115-Plf MCUElectronicsPfB

o

tt

F..

1 Radio Shack ZipZaps remote-COntrOl Ca!

3 o

1PrC16F684 1 MAX756 1 1N5817 Schottky

di,ode

1 LED i.00 pF electlolytic (rated capacitors least 10v)

DMM Needle-nose

0.1 p,F capacito! tYpe)

pliers

(Dremel Rotary hand tool tool) with carbide disk cutter Electlic

dliI1

e/er-inch

high-speed

14-pin, machined pin DfP socket (see text ) Tno-pin, right-ang,Ie st!aight-through conltec-

dlill

6^

Four-pin, !igbt-ang'le straight-throug'h connectol

i '^6

Solder Black

fwo-pin, througrh

wire

Red wile Y[ire-wrap

hd

Prototyping text )

KrazY GIue

6-32, bolts

epoxy

With the powersupplytested,you are now readyto start hacking into your ZipZaps car and turning it into a robot. In this experiment,you will be putting in nylon bolt attachment points for the PIC MCU PCB aswell ascreatingthe basicPCB cfucuitwith the power supply andPIC MCU socket.Thistaskis not goingto be easy, andyou will haveto plan for the future experimentsto make surethat enoughspace(and holes)is available for mounting additional hardware.As I work through this experiment, I will try to indicate the issuesthat you shouldbe mostawareol The prototypingPCB usedfor this experimentcan reallybe of any type,but I usedone with predefined power and ground tracesand horizontally connected holes.This simplified my wiring somewhatalthough it restdcted me in other areasfor which I had to comDensatewhenI addedadditionalhardware. Youdo noi

f)

PCB (see

2-inch-long

6-32 nylon

nylon

L'J *-, ,,

nuts

rr

haveto usea prototypingsystemlike I used,but you shouldread the restof this sectionto understandwhat prototypingPCB you want to useand how it is going to be mountedto your ZipZapschassis. Positionthe prototypingPCB over the Zipzaps chassisin sucha way that the PCB will hang over the chassisevenly.Do not positionthe PCB so it is above the empty spacein the chassisbetween the battery and the steednggear.Themountingbolts for the PCB will be gluedinto this areaand ascloseto the steeringgear aspossible.When the bolts are gluedin, it is important that the chargingcontactsand hold-downholesare not affectedin any way.If they are hindered,you will not be able to chargethe Zipzaps battery using the remote-controlunit. With the marksin place,find the centerof the PCB at this Doint and drill two e/er-inch holes 0.250-inch

5ection Thirteen Z i p Z a p s@ Ro b o t

L J

K

straightsocket

Four-pin, straig'htthrough socket

wi!e

PermaneDt malke!

Five-minute

I

H

Wire clippers ra'i

(anY

H P Ol

0. 01 pF capacitor

bir

c^l

at

5

*

307

*

Ff

n

,-t

P, {a li

ry

R lrr{

t ,

m

U A

w U

,Fl

g

o t{

{J

U

(} FI

rd p U

x

U H

A

I \o rl r{ $

c 0, E .Fl t{

o

9{

X

frl

away from the c€nter.ff the prototyping PCB is fully drilled (as mine was),drill out two holeq four holes apart. Rememberto keep the PCB centered over the ZipZaps chassiswhen you are doing this. Once the holes are drilled, run the nylon bolts through and screwthem down with some of the nuts. At the end of the boltg loosely screwon a nut and put Krazy Glue on the open face of the nuts at the end of the bolts.Carefully (making sure you do not trap any of the small steeringwires) push the open face of the nuts againstthe bottom of the chassisThe bolts should be solid to the touch in 30 secondsor so.The Krazy Glue actsasa mild solvent to the plastic usedin the ZipZapqso leave the assemblyin place for an hour or so for the Krazy Glue and chassisplastic to harden. When the Krazy Glue has hardened,remove the bolts and cut the bolts down to 1.25inch (3 cm). (You will probably have to loosen the nuts holding the bolts to the PCB first.) Insert the bolts into nuts,cover the nuts ald the baseof the bolts with 5-minute epory, and wait for another hour for the epoxy to harden. When the epory has hardened,run two nuts down the shaft 1A inch (1/zcm) and Krazy Glue them in place.Once the Krazy Glue hashardened,you can place the prototype PCB on the bolts and tighten it down when you want to test the robot. With the bolts in place,you will now have to cut down the original ZipZaps PCB.This is being done for two reasons.Fhst, you want to avoid any kind of contention betweenthe ZipZaps driver and the PIC MCU. And second,you want to make spacefor the two bolts you just installed. Before cutting the PCB with a Dremeltool and carbidewheel,I locatedthe four resistorsusedfor current limiting on the PCB and drew an indicator line on the PCB above them (see Figure 13-7)using an indelible marker. Cut the PCB along this line carefully,making sure you do not damageany of the marked resistors. Once the ZipZaps PCB has been cut, solder wires to the positive (red) and negative (black) wires leading from the battery to the PCB.Thesewires will go to a right-angle connector to be soldered to the bottom of the prototyping PCB and will need the straightthrough connector soldered to the other end. Next, solder wire-wrap wires to the endsof the four-motor driver and steering driver resistors(seeFigure 13-8). Thesefour wires will be soldered to another straighttbrough connector,which will go through another right angle connector and the bottom of the prototyping PCB.The ZipZaps chassisis now ready to be controlled by a PIC MCU! When I attached the PCB to the robot, I did it with the solder tracesup.This make soldering components quite a bit more difficult, but it ensuresthe PIC MCU power and motor/steering driver connectorsare easy

308

Figure l3-7 Mark cuttingline abovecuruentlimiting resistorsand belowblack blob

to solder and their whes do not snagor rub against sharp wires on the bottom of the PCB.The machined pin socketthat wasspecifiedfor the PIC MCU was identified becauseit can be soldered to the PCB from the topside (instead of only from the bottom side,asin a regularDIP socket). The circuit that you will be wiring to the PCB is the basicpower supply with PIC16F684(without the two LEDs) in Figure 13-9with the bottom right-angle connector usedto supply the 1.3volts from the Zipzaps battery.Again, it's important to plan ahead;due to my wiring placement,I put the MAX756 and its related discretecomponentsat the front of the robot, which left the rear of the PCB for the PIC16F684. When you have completed the assemblywork, your robot chassiswith PCB should look something like Figure13-10.You shouldstill be ableto put the ZipZaps chassison the Zipzaps charger,and it should work normally (i.e., the charger'sLED should start at red and changeto green when the charging operation hascompleted).Ifeverythingis correct,after taking

Fisure 13-8 PCB connector

l , e 3 P I C @l t C L JE x p e r i m e n t s f o r

the Evil

Genius

Zipzaps

' iI .

Fieure 13-9 ZipZapspower

the ZipZaps chassisandPCB off the charger,an LED placedagainstRA4 andRA5 (cathode)shouldstart flashing.Thereis no on andoff switch,the MAX756 will stop providing3.3-voltpower whenthe input voltagehasdroppedbelowits threshold.This shouldgive your robot a minuteor two of basicoperation,which shouldbe goodfor testingmostapplications. I found that althoughthe connectorswere quite reliable,the solderjoints and wiresfrom the battery and motor to the ZipZapsPCB would easilybreak. Ideally,the prototypingPCB would be permanently attachedto the ZipZapschassis(asis the original product PCB),but this is very difficult to do and still be ableto work throughadding(and debugging)the differentperipherals. Make sureyou plan how to con-

:-11 Figuref 3l0 wirhpnrrinlty ZipZnps chassi.: assembled PCB attached

nect and disconnectthe prototypePCB to the ZipZaps chassisso that the wire solderjoints receivea minimum of stress.If you don't,you will find that the wires will breakperiodically.You'll be left scramblingto figure out the causeof the problemand then fix it, with the wiresbecomingshorterover time. This is probablythe mostdiflicult assemblyexperiment in the whole book.Rememberto think about whereeverythingis goingnext,and try to keep everything aswell centeredasyou can.A few momentsforethoughtwill saveyou a lot of grief later.

5ection Thirteen Z i p Z a p s " R o b o t

309

Experiment ll7-lH TV FlemoteControl

Prc16F684

r{

38 KHz tR TV lemotereceivers coltrol

$'1

1 fno-1ine,

4r

1 10k lesistor I

16-column

LCD

100C) lesisto! 10k b!eadboard-mountable potentiom€ter

t'l

4? pF electlolytic capacrto!

Needle-nose pliers

al

B!eadboard

+J

Wiring

0.01 pF capacito! type)

kit

(anY

B!eadboard-mountable (E-Switch SPDT switch 8G1903 leconmended)

G.}

Breadboard-mountable momentaty on pushbutton

F.

Thlee-cell, pack

AA battery

AA alkaline

battelies

f-r

ffi H

I like controllingrobotsusingan infraredTV remote control;they are cheapand the coderequiredto read the data is surprisinglysimple.Other optionsinclude RF or soundcontrol,but thesetend to be expensive and"fiddly" comparedto IR control,especiallyconsidering that IR control is generallyhandledby the robot'scontrollingPIC MCU. In this experirnent,Iwill demonstratethe code and circuitry required to read an incoming IR signal and display it on an LCD. The IR signalproducedbyTV remotecontrol comesout of the receivermodulelooking (seeFigure 13-11).TheIR signalfrom the remote-controlcodeis

modulated with a 38 kHz signal that is only active whena low is desiredin the receiver'soutput.For hobby robots, I like to use the SonyTV codes,which consistof a PacketSrat followed by 12 bits in the format shownin Figure13-11.Thetiming of the different featuresof the waveform is basedon a 550rr,sT clock and consistsof differentmultiDlesof this time base.

"1"Bitl "0"Bit

0)

-:-T;.5

.r-l

ti &r".

Start(4T) Figufe

'13-'f'f

Synch "i'

(1r)

"0'

I

(1r) (2r)

IR remote-control codes

Figure l3-la

IR Rx testcircuit

{d I F{

310

l , A 3 P I C o l ' l C UE x o e n i m e n t s f o r

the Evil

6enius

Table 13-1 Codes LJEedbg the 5ong TV lFl Flemote-Control ZigZaDs Robol

B.ut!* 0x010

.PIP"

oxDB0

"2"

0x810

"Enter"

0xD10

"3"

0x410

"Display"

0x5D0

0xC10

"Mute"

0x290

0x210

"Recall"

0xDD0

OxA10

'Alrow Up"

0x2F0

"1"

'5" "6"

0xAFO

0x610 "8"

Ox2D0

0x110

'Arrow Left" 'Arrow Right"

oxE10

"9" '0"

0x910

"Menu"

0x070

"Power"

0x490

"Guide"

0x764

0x490

'oK"

0xA70

OXCD0

To read and displaythe IR incomingsignals,I came up with the circuit shownin Figure13-12.This is a modificationof the originalLCD displayexperiment's circuit,whichnow includesan IRTV receivermodule with the requiredfilter capacitorand resistor.The C programming languagecode for driving the LCD was translatedinto assemblerasasmlCD.asm,which can be found on the PICkit's CD-ROM.The actualcode that readsthe incomingIRTV remote-controlsignalis calledasmLCDIR.asm.Note that to simplifythe time delayqI createdthe Dlay macro,which will delaythe operationfor somesetnumberof microseconds. When I ran asmLCDIR.asmon the circuit shownin Figure13-12,I cameup with the codesin Thble13-1 for the different buttons on a universal remote programmedto output SonyTV codes.These different codeswill be usedfor controllingthe ZipZaps robot in the following experiments.

m t?t h+

J

g# *"€

r'*

i..*

# i-Et

0xC90 "Ch+"

0x090

'Ch-"

0x890

! ht qr.'

llB-Motor and SteeringEontrol Experiment

ry fli ,"{

Radio Shack ZipZaps remote-control ca! chass is Ptc16F584 PrototYpe Previous

PCB flon the exPeriment

4. ?k les istors 470O lesistors

{ !.s

ru

DMM Needle-nose Ilire

pliels

clippers

Soldeling

ilon

solder Wire-rirap

wj,re

With connectionsfrom the original Zipzaps PCB to the prototypePCB in place,the next stepis to make the motor and steeringconnectionsso that the PIC MCU cancontrol the motion of the ZipZaps chassis.

The connectionsrequirecurrent-limitingresistorsto ensurethe motorsand solenoidsare driven with approximatelythe sameamountof curent, that they perform asdesigned,and that an excessive amountof currentisn't flowing.Thisis an importantpoint because the PIC MCU will be driving high signalsat 3.3volts insteadof the 1.3V measuredon the oiginal ZipZaps. To calculatethe new currentJirniting resistorg I voltagedrop was assumedthat the base-to-collector 0.7V, and usingthe known basecurrent-limitingresistors.I couldcalculatethe exDectedbasecurrents.

5ectionThirteen Z i p Z a p s @R o b o t

311

*"3.

5C I

q , e*

.}

For the steeringdrivers,the basecunent is:

Zipzaps

t':r\ t,:,

v=lateering*3.3k = (1.3 - 0.7) isteeling

/ 3.3k A = 0.18 nA

To maintainthis basecurrentwith a 3.3-voltoutput:

i.{

t'1 f

v = isteering x Rsteeling Bst€€ring = (3.3 - 0.7) / 0.18 rnA = 14.{k

i

iJ, f'j

.; -{

With 3.3kalreadyin seriegan additional11.1kof resistanceis requiredfor the steedngsolenoiddrivers. Similarlyfor the motor drivers,the basecurrentis:

Figure l3-13 Zipzaps motor

a ! v = r l . f t t x z z u

,i:

i.".., = {1.3 - 0.'7) / 220 A

+-,)

= 2.'73 nl+

if]

To maintainthis basecuffent with a 3.3-voltoutput: - {

?

t-; ltl

R . . " " , r " n= ( 3 . 3 - 0 . 7 ) = 950O

F.!

,.:r l

':. : l rl,,.i

/ 2.'73 rnA

With 2200 alreadyin seriegan additionalresistance of 7300 is requiredfor the motor driversto be controlled by the PIC MCU With thesevaluesin mind,I testedan additional 10kfor the steeringdriversand 680Oresistorsfor the motor driversaswell asno additionalresistanceat all points.Totestthe actionof thesecircuits,Iconnected the transistorbases(with seriesresistors)directlyto 3.3volts.When the calculatedadditionalresistorswere in place,the motors and steeringsolenoidsseernedto work exactlythe sameasthey did with an unmodified ZipZaps.With no resistances in place,both the motors and the steeringsolenoidshad a lot more power.In an effort to find somebalancebetweenmore power and

Figure l3-fq ZipZaps robot prototyping PCB with motor and steeringtransistorbasecuffentJimiting resistorsconnectedfrom the PIC MCU socketto the backsideZipZaps PCB connector

burningout the motors,driver transistors,or depleting the batterytoo quickly,I found that 4.7k and 470f) werethe optimal additionalseries-base current-limiting resistorsfor the steeringand motor drivers,respecIively.T\e ZipZapsrobot prototypingPCB (seeFigure 13-13)wasupdatedappropriatelyand wired according to Figure13-14,and it ran usingthe softwarepresented in the next expedment.

i'i':

. !.t

i].

il

3L2

l , e 3 P I C @I I C U E x o e ri m e n ts f o r

the EviI

6enius

Experiment 119-BasicTaEk-Eontrol Softurare Pc/

Prckit"" 1 Radio Shack Zipzaps remote-control ca! chas sis P I C 1 6 F 5 84 Prototype

starier

Tool

Box

#def,ine Rc2 r #define RC3 t *define RC4 r RC5 r i r r

Earlier in the book,I demonstratedhow to run a motor with a fairly low frequencyPWM. I'm goingto takeadvantage of thatwork with the ZipZapsrobot because I wouldlike to usethe PlC16F6lJ4's builfin PWM lor modulatingI/R output.Theresultis ZipBase.asm, which hasa 30 Hz PWM lrequency,and provides32 PWM duty cycles,aswell asup to 1 ms betweenPWM stepsfor implementingsensorand control functions. To test out the connectionsto the ZipZaps chassis aswell asto get an idea of how long the batterywould lastwith a PIC MCU runninga stepped-upbattery voltage,I addeda numberof actionsthat take place over a 25-secondrepeating/l/e to demonstraterunning forward,forwardwhile turning right and left, stopping, and goingbackward. "zipBase

title t r i , r

-

zi.pzags

Robot

Ease

coale"

This Program Iroops orce every ns anil upalates the zipzarls Motor PI'iM (30,I{2 P!'Dt). The application also keeps lrack of the current time for the application.

.

FLia

t

heavily

.nn1,ida+i^n

ia

ba6eal on "asmMotor

2.asm".

Haralware No!€s: t PIC15F584 rurrnirrg at 4 MIIZ Using , Intelnal Cl,ock t RiA0 - Lef,t Light Senso! r RA1 - Rigbt Light Sensor r RA3 - Rear IR sensor t RA4 - Reverse Motor Control t PORTA, 4 #alefine ReversePin AA5 - Forwardls Motor Corrlrol t

PCB

kit

['orwardsPin PoRTA, 5 - Rigrht steeringr solenoid TurnRisht PoRTc, 2 - Left Steering Solenoid liurnl,eft PoRTc, 3 - Line FoLl.owing IR PWM - Object Detection IR PI4U

li{yke Predko 0s.01.25 LIST R=DEC rNcr,uDE "p16f 58{. inc rr CONFIG FCITEN OFF & IESO OFF & -BOD.OFF & CPD OFF & CP OFF & MC',RE OFF & PWRTE.ON & IIIDE OFF & ITiITOSCIO

variables cBr,ocK 0x020 RTC:2 r 55 Second RTC Directionr PWMDuty, PWMCycle t PWM Movemen! r variables Flag ENDC ;

Flag r #alefine

Bit Definitions F1ag, AppRun

#alefine

A)pReset

Tinecheck novl.w xornf btfss goto tnovlw xorwf btfss goto enalln

the r

alag,

Macro TvaLue, fiIGE Tval"ue RTC + 1. rt STATUS, Z lilotv€cto! LOW Tvalue RTC, w sTATus, z Notvector

if

Application

0

i

Set

1

i

Set if application Reset Coale to Run

Notvector

FAGE Mainline org

0

nop clrf,

r For PORTA

5ection Thirteen T i p Z a ps o Ro b o t

ICD D€bug

t Assune is Low

Everything

5r5

ft! !

'>

novwf, Ilovllr ovwf, clrf

cMcoNo b,00000001, a.DcoNo TuRo

H c,-J

F,t-l 3 I

I

EnabLe

STATI'S, RPo b,11010001,

movwf lrovlw

novwf bcf

OPTION_REG ^ 0x80t b,00000011, r t ANSEL ^ 0x80 b,00010000, r t A.DCONI ^ 0x80 b,001111, r TRISA ^ 0x80 b,110011' , i ERISC ^ 0x80 STATUS, RPo

bcf

MTCON,

cllf cltf clrf

Flag Pl[{Duty PWUCycLe

cLrf

Dilection

movwf novlv lrofisf novLw

Loop: btfss goto bcf

ToIF

INTCON, r0lr $-1 MTCON,

llDc

1'!lR0 aa a P!l!l

ADC Clock

Enable

l{otor

Enabl€ Bita

gtse€ring

as

tfufler

anal Wait

for

Check to Upflate llotor If Duty > Cycle, then Off,

sublrf movf iorftd btfac

PWUCycle, PORTA, w 1 << 5 Directl.oa,

xorlw btfac andLw movwf

(1 << 5) + (1 << 4) t TRISC Revelse STATUS, C b,001111, Uoving , Notbing PORTA Value i Save ltotof

incf

RIC,

blfsc incf

STATUS, z RTC + 1, f

incf

P$Dlcycle,

f

bcf

Plglqcycle,

5

!h€

w

f,

t Going Fornarda or i Forwarala

i Incredreat , CLock

IrooD t Finiahetl, A.rounal Again

TestApplication Software:

t i r t r r t r

-

Test

Motor/Sbeering

Thi6 Program ia a baEic teal of lhe ZipZaDs Robot llotors anal St6€rlng, Th€ cofiuranats ar€: 1. Dlove f,orwatta for 5 S€conala at 10 Secoadg 2. llurn Right at 11 gecoatlB for 1 gecondl 3. firrn l.ef,l at 13 g€conflB f,or 1 g€conal 4. Stop at 15 Seconala f,o! 5 Secoatlg 5. co in Reverae al 20 gecontla for 5 geconalg 6. Rese! RrC andl Regeat at 25 Seconala

Haralware NoleE: i PIC15F584 runnl.ag at { UItz Using t rnl€lna1 clock t nAo - Left lj.ght Sensor r nA1 - Right IJLght sensor t RA3 - R6ar IR genaor , ItA{ - Revera€ llotor Coatlol t *tlefine R€versePln PORTA, rl RiAs - Eorwarala l{otor Contsrol t EorwardtsPin PORIA, 5 *tlefin€ RC2 - Rlght Steeling sol€Doial r TurnRight PORTC, 2 *fl6flne gteeling RC3 - Left Sol€noid r Turnl€ft PORTC, 3 #alefin€ RC4 - Lia€ Following IR PWM r RC5 - Obj€cl Deleclion IR ItwM r

r r

lbe

MYk€ P!€dko 05.01.25 LIST R=DEC INCLI'DE n916f 68{. lncn

ReaMme

i Notse. RoLls , 5 5 a

over

a!

FC!IEN_Orr & _IESO_OEF & _BOD_OFF & *coNFIC -CPD OFF & CP-OT! & _IICIJRE_OFE & _PWRTE_ON & _t{Dt[_oFt' &,INTOSCIO Valia.blea CBLOCK 0x020 RTC:2 Dir€cEion, PlcuDuty, i

ftr

lhe FVIM i Inclenent r eIc1e counl , Ma:limrm of, 32 i qfclea

##** - Pul other sensors Here ###* - Put in Rdnole Contlol Poll E€le l++#+ - Puts in seEsor State lttachine - rJigh! sensola (1 Pull per 32 cycles *##* -

td-l SJ

##**

"Zil)ulrchk titsLe cE)erationtr

TuRo tso

PVlMDuty,

0

##**

Put oDeratinq IJogic Here (1 Per 32 cyclea) /Ne€ds sel FIag - Check "llDDRea€l' lo ge€ if ApDLicatioa is to be Restart€al - Relrot€ conlroL (uov€ or Dir€ct SloD) ReEets trAlrpRuan FIeg .Recall' - Reatole Contfol Sets ,,ApDRunn t.lagl

€nil

BitE

novf

rtr

##**

-

looD

NoE Uoving at Eirs! gtalt at tshe B€gLaning lloving Forwaltls

t Reaet t Next

#**#

to

Selecl Foac/8

for r wait t Overfloqt

r t r r

, r r r , r r r

RAo/RA1 (AI{0/}N1) ADC InputB

for r Wail t OverfLow

ToIF

on llao

i 1:4 Preacal€! t ll,lRo

r r r i

Uolorlrpdale:

!r*

,

baf novhr

movwf movlw

, \l

co4Daratora

r ugitrg t Base

*{

e{

i

**#* *###

314

Pwucycl€

r 55 Seconal RTC i PvtM ltov€ment ; variablea

Elag ENDC FLas Bi! Def,initiona , AppRun F1ag, *d6fine

1 Sdrlp1€l8 crrcl€s] - Object (1 P€r 32 Cycl€a) Sensing - IJine S€nsing (1 Per 32 Cycles)

l , E 3 P I C @l l C U E x p e n i m e n t s f o r

the Evil

0

r se! if, t ApDlicalion i Run

Genius

c.rn

+ilef,ine

AppRes€t

Macros t Tinecheck novL$r xonrf, btfss golo movlw xornrf btfss goto

r

Flag.

Macro rvalu€, HIGB walue RTC + 1, w STATUS. Z Nolvector LOW lvalue RTC, st STATUS, z Notvector

1

r Set if Reset , Applicatiofl r coale to be Run

Notvecto!

i

cLrf

PoRTA

clrf novlw

PoRTc 7

movwf movLw

CMCONo b'00000001'

novwf cLrf,

ADcoN0 Tl,tRo

For

ICD Debug

r Assume ; Everjrtshing

is

r Elrable r RAo

A.DCon

TMRo as a r using r Pwll Base

STATUS. RPo b,1L010001,

movwf movlu'

oPTIoN REG ^ 0x80r b,00000011,

monwf movhr

rrNSEl ^ 0x80 b'00010000'

movwf movlw

ADCOIiII ^ 0x80 b'001111'

lnowf rnovlw

TRISA ^ 0xg0 b'110011'

movwf bcf

TRISC ^ 0x80 sTATus. RPo

bcf

INtcoN,

clrf clrf

Fl.ag RTc

clrf clrf

REC + 1 PWMDuty

i

clrr

pi^,Mcycle

j Silii "" "n.

clrr

Direcrion

; ;::iilT:,-",",

movf

I!fllCON,

r,ow

r rurn off r Conparators

bsf novlw

goto bcf

l'

xorlw blfsc andlw MOVWf

{1 << 5) + (1 << 4) STATUS, C b'001111' PORTA

0

btf,sc incf

STATUS, Z RTc + 1, f

ToIF

r 1:4 Plescale! r T!tR0

S-1 IN!!CON, ToIF

PWIilDuty, w

to

r AjA0/RA1 (ANo/AN1) t ADC Inputs , i

s€Lect ADc cLock as Fosc/8

r Enable r Bics

Motor

t Enable r Bits

Steering

for r wait ; owerflow r Res€t t Flag|

TorF

Going Eorwarals Forwards or Rev€rs€? TRISC Reverse

, , t r

Movingf r Nothing i Save Moto! Valu€ Increment

incf

PWUCycl€.

f

bcf,

Pmlcycl€.

5

Not

TMRo to

Real

lloving

for r wait r Overfloxr

Tine

at

Tiner

r Reeet anal wait r for Next r t r r

check !o upalate the MoEor If Duly > Cycle, then Off

r ; , , , r r

##f* *#** #### ##*#

t i r ; r i r r

#*##

#**# #***

#**# #### #*+#

-

Real,

Ro11s t No!e, t a c 5 5 s

Over

Increment the PWM cycle count Maxinum of 32 cyc1".

i r , ;

0

nop

IJoop: btfss

PwMcycle, PoRTA, w 1 << 5 Direction,

i

PAGE Mainline org

subwf movf iorlv btfsc

Put Other Sensors s€re Put in Remote Control Po11 sere Put in Sensor stat€ Machine - Ligh! (1 Ful] per sensols 32 cycl.es - 1 sanpl€/8 cycles) - objecl (1 Per 32 Cycles) sensilg - line (1 Per 32 Cycles) sensing

- Put operating logic aere (1 Per 32 Cycles) /N€eds Set Flag - Check nAppReset. to se€ if application is to b€ R€starleal - Ramote Control (Move Direct nAppRunn FIag or S!op) Resets oRecallr - Remote Cont'rol Sels "appRun" Flag

Molor Check Test Program: r Move forvrarala for 5 Seconfls at 10 Seconals r 1. TryForwarals: Timecheck 10000. Atlssec novlw 0x1F r Go Forwatals at r Fu11 Speeat f,or 5 s novwf PWMDuty bcf, Direction, 0 goto l"oop Atlssec: Timecheck 15000. TryRight clrf PI{MDuty goto Loop

r at

15 Secondls?

r Yes,

rufn Right at 11 seconds r 2. TryRight: Timecheck 11000, All2sec TurnRiEht bsf goto rJool)

f,or

Slop

Motor

1 s€conal

Atl2sec:

';::"n"ni3lll;nlo""" goto

Loop

Turn lr€ft at 13 Seconale for ; 3. TryL€ft: Tirnecheck L3000, Atl4sec bsf turnleft goto Loop AtL4sec: Timecheck 14000, bcf Turnlef,t gotso IJooP

1 secontl

TryRever6e

S e c t i o nT h i r t e e n Z i o Z a o s @R o b o t

315

t {. t 5.

Stop at 15 Secontts f,or 5 Seconals G o l n R e v e l s e a t 2 0 Seconala for 5 Secontls

Timecheck 20000. nrovfnr 0x1F movwf, bsf, golo

PwMf,)uly Direction, IJooD

At2ssec at i Go Fofi^rarals r F1rll Speeal for

5

0

Res€t RTC anal Repeat r 5. At25s€c: Timecheck 25000, Loop clrf PWMDuty eLlf RTc + 1 cllf RTc

25 secontls At 25 seconals ? Not thele, R€peat Yes. Stop Motor CLea! the R|rC

Einish€dl, loop Alounil Again

As part of the developmentof this application, you'll seethat I cameup with the TimeCheckmacro, which will executethe codefollowing it when the ,'ealtimeclock (KlC\ variablematchesthe numericvalue. The RTC variableis incrementedonceeverymillisecond, sofairly precisetimingsare possible.When you look at the operationof the ZipZaps robot in this experiment,you'll seethat the motor is runningfor 5 seconds. And I want to wam you:The robot can go a long way over 5 seconds. Fortunately,whenthe robot hits a wall or other obstacleand stalls,it doesnot burn out.This is why it wascriticalthat I spenttime understandingthe motor and steeringdriver basecurrentsand addingaddi tional basecurrent-limitingresistorsto ensurethat the driverswould not havetoo much cunent passinq throush them.

Experiment laO-lR FlemoteControl

Radio Shack Zipzaps lemote-control car chassi s 1 Prc16F584 1 Prototype

PCB

1 38 kHz IR TV lemotecontrol leceiver 4? pF electlolytic caPacr!or DMM Soldering

10k resi.stor iron

100C) res isto!

SoIder Slire-r,y53" "r1t.

Beforeyou ran the Zipzaps robot in the previous experiment,you may havedoubtedhow fastthe Zipzaps robot could go.After you ran the experiment, you probablyrealizedhow difficult it would be to control the robot usingjust softwarewithout any type of feedback.In this experiment,you will modily the prototypePCB circuit (seeFigure13-15)so that the entirerobot canbe controlledby a TV remotecontrol setto SonyTV standards(reviewedpreviouslyin this secnonr. The remote-controlreceiverwasaddedto the rear of the robot (seeFigure13-16)asthis wasthe easiest

316

placeI couldfind for the circuit,and it will be usedin a later experiment.The output of the receiverdrives RA3, which canbe usedonly asan input.This wasan importantconsiderationbecauseI wantedto make sureI left the driver valuesopen for the remaining experiments. The applicationcodepolls the IR receiver,waiting for a signalto comein. The codethat processes the signal wastaken directlyfrom the previousIR TV remote-controlexperimentin this section(which alsoallowedme to usethe codesthat wererecorded duringthis experiment).Thebutton commandson the remotecontrol are usedto drive the ZipZaps robot forward (while optionallyturning left or right) or backward (while optionallyturning left or right).The PWM

l , E l P I C @I ' l C [ E J xperiments fon the Evil

6enius

valueof the motor driver can alsobe changedby using the volumecontrols.In the code,ZipBaselR.asm, which is an enhancement of the previousbasecode, you canseethat hookshavebeenput in for the remote conhol to be usedasthe tool that startqstops,or suspendsthe executionof a testprogramthat hasbeen addedto the applicationcode. As you controlthe Zipzaps robot,you'll probably noticea coupleof things.First,running the Zipzaps robot by remotecontrolis a lot of fun-arguably as muchfun asthe originalZipZaps,but different becauseit is just aboutimpossibleto spin it out or slide

it on the floor.This changein operationseemsto be due to the additionalweightof the prototypePCB and its electronics. So,what wasthe advantageof making thesemodifications?After severalhoursof work. have you simplyrecreated the Zipzaps? This is not quite true,the little robot you haveis capableof a lot more asI will showin the remaining threeexDeriments.

t:t:t:

{$

,i1'!

r-!' t,-l l'-*

Zipzaps

t{q

I

{, *rr

Figure 13-15 ZipZaps IR

Fiqure 13-15 Rear-lookingIR receivermounted underthesurfaceofthe ZipZaps robotprototypePCB

; f

:

fa,

ExFeriment 121-LightSensorsand LightFollor-uing

q,?d

|-1 {il Radio Shack zipzaps remote-cont!oI car chassis I

P r c 1 5 F 5 84

1

Prototype

ir:i

PCB

Lj.qht-dependent tors

resis-

i1;I :.{

10k resistors DMM

".,.i

Soldering

iron

SoLde! Wire-wrap

wile

A basicfeatureof any robot is the ability to senselight and dark and,ideally,to do it from multiple pointsof view so that comparisonsofits environmentcanbe made.In this experiment,you are goingto giveyour

Zipz^ps robot rhe gift of sight-that is,two lightdependentresistorsthat canbe usedto seekout or avoidlight in the robot'senvironment.Adding the two LDRs aspart of a voltagedivider is quite simple(see Figure13-17)and takesadvantageof the ADC module built into the PIC16F684. As you canseein Figure13-18,Iput the LDRs abouta third of the way backfrom the front of the robot, with eachone pointingoutwardat 45 degrees. This giveseachLDR a uniquepoint of view.This

5ectionThirteen Z i p Z a p s @R o b o t

3L7

.i.*;

:gJ !'r...4"

:-i l.t?

i.a i :

{_i *? t'l i

1..l

.:-1 e1 11i

ai

placementof the LDRs allowsthe robot to determine which sideis brighter and whetheror not to turn towardit or awayfrom it. The applicationcodeZipBaselDR.asmis an enhancementof ZipBaselR.asm,asit providesan ADC operation(on RAO and RA1, wherethe LDRs are connected)every4 ms.EachLDR is sampledand the resultsare storedfor retrievalby an application. Included in the code is a simple llglrr seekerlhat e\ecuteswhen the remoteconkol's Menu button is pressed.

proportionalsteering,guidanceto a light sourcecanbe gentlerandnot so startlinglyjerky (when the robot turns towardthe light).TheLDRADC valuesare ADCValueL andADCValueR in the applicationcode. I found the robot'sability to hit a flashlighton the floor (the light beamfor it to follow) waslargely dependenton how quickly the robot's motorsturned. The fasterthe robot moves,the later the steering changetakesplace(the decisionis madeevery100 ms),andthe more likely the robot will be to missthe flashlisht.

The light-seekingapplicationturns the wheelsonly whenthe darkerLDR returnsa valuethat is twice (or more) the valueof the lighter LDR. Thisvaluerepresentsquite a drasticchangein light and waschosen becauseof the all-or-nothingoperationof the ZrpZaps chassisternarysteering.In a more typicalrobot with Zipzaps

&."{ i

a

fi1

$l&*

ts{

Experiment laa-lH Bbiect-Detection Sensors

i

t Radio Shack Zipzaps remote-cont!oI car chassis

gV

1 Prc16F584 1 Plototype

PCB

38 kHz IR TV remotereceive!s colrtrol Re d I.ED

H

IR LEDS 10k !esistors

l1!

DMM

1k resi stors

Soldering

100k resi stols

So 1de!

47 /rF el.ectrolytic

VIire-vrrap Length sh!ink

{.,4

*at

of 5nm heattubing

i 6 t

318

l,e3 PICo llCUExperiments for

the EviI

6enius

ZipZaps Battery

t r l

fr

n o

Plc16F6B4

o100 uF 5

0.01 u

F

L

.

410

z

1

8

4.1k

1

4.7k

8

MAX756'

f tt

Reverse FoMards

*J"

RightSolenoid

;J

LeftSolenoid vdd

100 -lI

!

1k

47 uF

T __-l_ -:_

:

100

100

47

47 uF

uF

t/R

-'1I

E\.'

r\J

vdd

Top Side t/R LEDs

l i

t t:

6*"* '"5 '

Figure 1319

Zipzaps complete :t i

In the lasttwo experimentsof this book,I will demonstratehow the IR sensorscanbe usedto detectobiects and data aroundthem.This will be doneby usingthe To IR reflectiondemonstratedin other experiments. the placed around detectobjectEfour LEDs are perimeterof the robot that will drive out IR pulses, which,if reflected,will be pickedup by threeTV IR receiversaroundthe perimeterof the robot.By doing "senseof touch" with this,you are givingthe robot a

Figure l3-e0 Zipzaps robc,twith IR LEDs and W r emote-controI receivers

the two front-lookingIR receiversand the rear IR receivergivingthe robot someideaof wherethe object is aroundit. To modify the robot for this task,I would like you to add the six LEDs (five IR and one visible)to the prototypingPCB,aswired in Figure3-19.EachLED shouldbe pointingin a differentdirection,asshownin Figure13-20.After you havedonethis,pleaseadd two IR receiversto the front of the robot.To avoidproblemswith conflictingIR signals,the receiversshouldbe on the undersideofthe robot (seeFigute 13-2L). To test the robot'ssenseof touch,pressthe Guide button on your Universalremoteafter buildingZipBaseObj.asmand loadingit into your robot.Thiscode continuouslychecksthe perimeterof the robot, every four PWMCycles. I found that I had to put smallpieces(0.5to 0.75 inch long,or 1 cm to 1.5cm long) over the IR LEDs to get reliableoperationof the sensor.But, it is amazingly reliable for eachof the three IR receivers.(To test the operationof eachreceiver,wrap the other two in black electdcaltape to preventIR signalsfrom reachingit.) The stateof the IR receiversandwhetheror not an objectis aroundthe robot canbe polled by checking the PFrontRIR, PFrontLIR, and PRearIR flags.

5ection Thirteen Z i p Z a p s @R o b o t

1 **€

r* :*i.

r} i,-'f,

ri3 :,.f1

ts* F&

319

Experiment 1a3-lH Line-FollouJing SensorE

u.;

.J!

1 Radio Shack Zipzaps remote-cont!oI cal chassis 1Prcl6F684 1 Plototype

PCB

rxt f.{

,'*

:i-**

{J P*

b&6 !

Thislastexperimentis really a follow-up to the previousone.However,rather than sensingobjects,the downward-pointingIR LED at the front of the robot (seeFigure13-21)is directedtowardthe surfaceon which the robot is runningand if the surfaceis white,it is reflectedbackto the IR receivers.(Use a oieceof heat-shrink tubingto directthe LED rowardthe running surface.)The applicationcodeZipBaseline.asm is a modificationof ZipBaseObj.asmand usesa second PWM output. title

M 9,s{

r"d 3 I

,'ZipBaseline

-

Zipzal,s

Robot

Base

Codler

"zipBaaeobj.aslln urith lJine SensorE AaLleal. t t Earalware Not€s: ; PIC15F58{ run.Ding a! 4 Mttz Using tshe t rntelnaL t clock AA0 - I,efts Light. S€nsor r aA1 - Risht Lights Sensor t aiA3 - Rear IR Sensor , *tl€fine R€alrR PORTA, 3 RAlt - Reverae Motor Conlrol t ReveraePltr #al€fine PoRTA, 4 RA5 - Fonrarala ![otor r Control For$aralBPin #tl€fine PORTA, 5

;\t

*C2 t #tlefine RC3 ; *alefire RC4 r RC5 r

- Riglrt Sleering Solenoial TulnRight PORTC, 2 - IJeft St€eling Soleaoitl TurnLef,t PORTC, 3 - IJine Following IR P!{}I - Object Detectsion rR PVUI

IR Coale Table: t Buttono EQU 0x910 Bulton1 EQU 0x010 Bulton2 EQU 0x810 Button3 EQU 0x{10 Butstotr{ EQU 0xC10 Buttons EQU 0x210 Button6 EQU 0xA10 ButtsonT EQU 0x610 ButtonS EQU 0x810 Buttong EQU 0x110 A.?lowltD EQU 0x2F0 ArlonDn EQU 0:.lAF0 AlrowlJt EQU 0x2D0 ArrowRt EQU 0xCD0 volurleu EQU 0x490 volumeD EQU 0r.C90 Chaa€IU EQU 0x090 chauelD EQU 0x890 OKButtn EQU 0nA70 PwrButn EQU 0x490 ![enuBtn EQU 0x070 EnterBt EQU 0:1D10 R€caIlB EQU 0xDD0 PIPBUIn gQU 0xDB0 DiEpBtn EQU 0x5D0 r'tut€Btn EQU 0x290 euitleBr Een 0x764 r

Myke

Prealko

t LIST R=DEC INCLUDE "plSf68{.incn & _BOD_OFF & -CONFIG _I'CMEN_OFF & _IESO.OFF _CPD OEE & _CP_OFF & MCI,RE OFF & PWRTE OII & rirDtt_oFE & _IN:losclo

ua ;?

Varj.abLes CBIJOCK 0x020 i, DLay RTC:2 Difection, PllllDrty, t

n€ ai]:

::{ 'i -"a

Figure l3-?l The businessend of the ZipZaps robot downward-pointingIR LED usedfor linefollowing

320

A.DCCycle, llovecount€r,

Pll!,lcyc1e

ADCValueL, i|Dc\IalueR r .e.DC Valiables NewPvn4Duty, volcounter

rRcoale:2 obj ectPliu

l , E 3 P f C @H C U E x p e r i m e n t s f o r

r 55 seconal RTC r PWUUovetn€nt t varj.abL€s

r Set

the EviI

Genius

Objec!

PWII

objlroEtR, LLnePl|!l IJi!€rrontsR, Flag:2 ENDC

objFroatl, t in€FroDtl

flag r *defj.n€

Bl.l D€f,iaitiong ApDRun Flag,

0

*d6fire

AIrIrR6B6t

rlag,

1

*dl€fin€

Lighls€ek

Flag,

2

#dlefine

objeelgeaae

Elag,

3

*dlcfine

PFrontRrR

r1ag,

{

*dl€finc

PFtontLrR

!1ag|,

5

#dl€f,ine

PRoarIR

Flag,

5

*alefi[e

Linese

llil€fiu€

r,ProatRrR

*dl€fine

aor

LFrortLIR

lilacroa t Tlmech€ck novftr xoliff btfaa goto nov1lr *orcf blfrrs goto €ndn

!1a9,

7

Flaq

+ 1,

FIag

lllacro Tvalua, EICN Avalu€ RTC + 1, rt STAfgS, Z Nolvector I,ow l\talue RTt, td STATjttg, z Notsvgctor

+ 1,

t t i r t r t r i i i , , , , r t r r t 0 r r 1 r ,

set if Aglrlicalion can Run set if, ADItIicatioD Reaat Cotl€ to be Run get \,rheB Lighl geeking ltoale ia Enableal get when Doirg an Objecl S€nBe s€t nb€lr obj€ct to lro|tt Right get wh@ object to Froat Left Set when object to B€ar get whea Doing a lJl.rt€ g€nEe get vlh€lr Lin€ to !!ont Righl g€t wh€n L1n6 to lro'lt IJ€fE

cltcoNo b,00000001' ADCONo I1{R0

novhr

b,00001100'

novwf novlw

ccPlcol{ b'01111000'

novwf

T2COII

bsf nov].w

STATttg, RPo b'11010001'

novnf novhr

OPTION_REG b'00000011'

nonrpf llovlw

INSEL ^ 0x80 b'00010000'

novwf, Dovhr

aDCONI ^ 0x80 b'001011'

lrovlrf movlro

TRISA ^ 0x80 b'110011'

movwf bcf,

TRISC ^ 0x80 STAmS, RPo

bcf

MTCON,

clrf cLrf

Flag PllldDuty

clrf Begirnlng clrf nrovlw

lilacro EutEoa, HICH Buttorl IRCoale + 1, !t ETATI'S, z Notvectora IloW Buttoo IRCod6, rd STATItS, z Notv€Ctor

t For

clrf

PORTA

clrf

PORTC

ToIF

ICD

t aggurne

Section Thirteen

Etralcle

r i ; t

UEIng mrRo as a Pl{Dl Baa€ Enable BaEic Pinl lloal€

ADC oa RAo

tttR2 Ple

lritsb

i 1:{ PreEcaL€r t rltRo

!o

r RAo/RA1 (Ar[0 /Alr1) t lllrc IiDutE ADc clock t Select i aB Fosc/8 , Enab1e Motsor ' IJED BitE

subwf novlw iorlw btfsc

PwMC!rcl€, 0 1 << 5 Dlrectlon,

Ena.ble Bits

iollrd btfac iorlw blfac

1 << 2 PFroDtt rR 1 << 2 PRearIR

5 ct

ts N I

Sle€ring

H llllRo

tso

w r{

Not llovlng al !lrat sEarE ats the

Fr,

5

o

o

f,o! r Wail , Ov€rflow aatl t Reset i for Next

P

llir|er

ts

o

l{ait

t check !o qDtlat€ i the llolor t If Duly > Cycle' t th€n Off

w rd

0

i Force tlotorE i Gioiiag EollcaltlE o! i Forieerala i Reverge?

Movinq t Nothing Ch€ck lo r Object ' PUt IJED ON

Z i p Z a p s @R o b o t

, ,

{

F'

5

q

v,

gav€!€RTA PFrontRIR

3 o

I

(1 << 5) + (1 << 4) SllAlrug, C 0 Objocls€nae

golo btfac

F.

qt

$ - 1 INTCON, TOIF

PWMDuty,

o

rt

(,

&

Fo:.warila i Moving at ttl1 t gtart t SPeed

IN!!CON, ToIF

rovf

x

rd

I

i i

i i i

D€bug Evertthiag

,

for , vfait i Ovelflolt

MotoruDdete:

0

co![)alatora

NelrPlllllDutY A.DCCycle llrcvaluelJ aDcvalueR

grolo bcf

nor.Iw btfsc novltr btfaa

noD

^ 0:<90 t

DLrecllon 0x1F

IJooIr: btfEa

liloweclo!

i

t Enable i a 15x

PllIlCycI€

rlovtrf clrf clr! clrf,

PEGE llaLnlln€ , olg

novwf movltd lovwf clrf

Nolv€ctor

EaDIay llacro C:icles Dovlw HIoH ( (c5zcIes / 5l + 256) Dor'rrf DIay Dovlw LOlv ( (C'ycles / 5l + 256t -1 atldllw blf,ac STATUS, Z tlecfaz DIay, f, qoro $-3 6rdn Bultoacoq)are novlw xorilrf btfsa golo mov\r xorcf btsfds gOtO eddm

t{l

objRear

o 5 u

o

If Sonaor ait get, LED Or

r't

(t 32t

i.orlw 1 << 2 SavePORTA: movwf PoRTA

rrovlw i

u iJl 3**

w (J!

F"r &*{

t t'g

:

Save

lilotor

value

R€al t Incr€lrent r Time Clock blfac incf

STATI'S, z RTC + 1, f

; Note, Ro1ls t a l 5 5 a

i.ncf

P$lMcycle,

f

bcf

PWMCycIe,

5

movf

lfovecounter,

btfsc goto alecfsz

sTA:rgs, z Nouovechang€ llovecourter,

golo btfac

Noltov€Clrange Lighls€ek

goto clrf

DolJlghtseek Pl{tlDutsy

bcf bcf goto

lltrnlJ€ft TulnRtght Noltovechaage

f

t Direct t llove?

Control

; Decrement t Counte!

Move

r h IJight r uoale?

Seeking

C1€ar , If Zelo. Duty , !4oving , Anal Stop Turning

Doligh!Seeh: movf, ADCVaLueIJ, ttt sublrf A.DCValueR, w blfaa STATUS, C groto DolightseekRight Dolightseeklrefl:

r IJook for t Is Righ!

Tutn > IJeft?

< Rights,

*** ;i

;t i - J

F*{

"i4 a-t!

STATUS, C ADCValueR, A.DCvaLu€L.

movltr btfaa novl{r

0 sTATus, C 1 << 3

movwf movl$

PORTC 100

movwf goto

trlov€Counter NoMovechange

DolJightseelrRight

a, yx LI4

r Is l.ef,t , eisht./2?

t ,

!!urn Light

:

STATgg, C ADcvaluer,, ADCValueR,

movlw blfss novlw abverf nrovlw

0 STATUS, C 1 << 2 PORTC 100

nov$f

llovecounter

<

rowarals

i Continue t aDoth€r

bcf rrf subnf

for 100 ms

< Left, r Rigbt Towarala? t tura w sr

i ,

Is Right IrefE/2?

r furd

<

To!,,a!ala

r Codtinu€ r anothe!

Nolilovechange: btfEc RearIR

rRR€afl: btfa6

Ligh!

for 100 ma

call

CountHigh

btfsc goto

STATUS, C Loop

goto

322

t IR Value Being i Recei.veal?

F-1

t l,ine to i Again

12

call novlw subwf

CountlJow 80 Dlay, w

llf llf

IRCoaIe, f IRCoale + 1,

dlecf,sz goto

i, f IIlRIJoop

t Carry Sel, r Erfor/Igrlore

go High

t

Cclt[laEfl

t

Ca!ry

i

R€peaE?

Sel,

1

f

anat lr6ft i Forwarala Bultoncompare Buttonl, CheckButtoa2 nrovhr 2OO i Run for 200 ns novrrf lttovecounler novf, NercPI {Duty, w novrrf, PlmDuty bcf, Direction, 0 t Moving Eofirardts bsf Turnlreft bcf rurnRight bcf .ltpDRun , Tuln Off Plogram bcf IJightseek r Turn Off lJight , g€eking lroop

Butloncorq)ar€

t forwarals

Button2,

movltr movlrf novf lrovrf bcf bcf bcf bef bcf

2OO Movecounler NewPt0tDuty, Pl,{llDuty Di!€ction, Tulnl"eft TulnRight AppRun Lightseek

gotso

LooE)

CheckButston3 r Run for

200 lla

w 0

r Moving

Forlralats

t Turn Off r Turn Off r Seeking

Program Light

CheckButlor3: i ForwaralE arrd Right qrtton3, Buttonconr9are Ch€ckBubtons movlw 200 t Run for 200 ns movfif ltovecounter novf, N€wP$uDuty, w movlrf PWMDUEy bcf Dir€ction, 0 , ltovLng Eoryrarals bcf Tuln]Jeft bsf liuraRigbt bcf, AppRun i Turn Off Progren bcf Ligbtgeek , Turn Off lJtght i seeking goEo

IJooP

Ch€ckButton5:

Sensolcheck

RearrR

Get

for t IJooD llere r Each Bit r l4ust be Applox

ButtoncodE)are Bultons,

goto

3*{

!t !r

IRItIJoop:

CheckButton2:

r Tuln Towartls? bcf lrf, subrdf

to

movwf

golo

r IJeft

t Want , Bits

ovet

the pWM i Incr€m€nt t C-yc1€ counl of 32 i Maxifi4 t c:'cLes f

L2

pw,tDuty

cllf bcf bcf clrf bcf

TurnLeft Turnlight llovecounler AppRun

bcf

lightseek

goto

Loop

l , P 3 P I C @l ' l C UE x p e r i m e n t s f o r

the Evil

r StsoD CheckButtsoaT r Stop

, t r t

Everylhing

StoD Applicalion Running Tuln Off, Light S€eking

6enius

anat IJefE Ch€ckButlon7: t Revels€ Buttson7, CheckBulton8 Buttoncompare 200 movlw t Run for 200 ms Movecouater novwf NewPWUDuty, !t novf PWUDUtY novDtf Direction, 0 bsf t Moving Backwartls b8f TurDleft rulnRight bcf bcf AppRuI r lPurn Off Plogram rJight bcf r,ighlse€k r TurD off t Seeking gtolo

EnterBts, Buttonconpare ap9Ru.u bsf bsf AtpResel goto IJooP

uenucheck

FoIIo''? r light Guitlecheck t SloP A.t[r Previoua , Applicetsion , Enable lJight , Seeking Moal€ , DiaabLe object uoal€ r seeking Line t Diaable

Menucheck: u€nuBtn, ButtoacdE)are ittpRun bcf bsf

TJightseek

bcf,

Objeclsense

bcf

Linegengor

movlw monwf movf, movwf, bcf bcf bcf golo

100 Mov€Counler NewPlCUDrty, PlllllDuty Dir€ctLon, TurnlJeft firrnRigrbt l.oop

*

IJooP

&6 .--

CheckButtsonS:

Buttoncompare rnovlw novwf novf movwf bEf, bcf bcf, bcf bcf, goto

ButtonS,

200 lilov€counler NelrPwltDuty, PlillDutsy Dir€cELon, Turnrr€ft rulnRlghts A)DRua lJightgeek

checkButlong r Run f,or

200 ns

w , Moving

0

Eackwartls

t Turn Off r Tuln Off i se€kingt

Program Lighl

Guiatecheck: Butstoncompare

0

PWll checkvolqp ! t Increase voLnneu, ChecllvolDn Buttoncompare novf N€wPWMDuty, w r At Limit? xorLw 0x1F gTAmS, z blfsc goto LoqP f iacf volcounter, r Delay lx qycle , Get 3s Range 0 btfs6 volcounter, , nr1l i coflErol f incf, N€rrPwllDuty, goto looD CheckvolDd; t DecreaE€ Recallcheck volun€D, ButstoDcolrDare movf, N€wPWUDutsy, f ; At lrinits? STAIUS, Z btfac gofo LoqD f incf, volcounter, r D€lay lx i Get 36

btf8a

volcounts€r,

0

atecf gotso

NewPwMDuty, LooP

f

RecalLcheck:

Bultoncorq)are RecalIB, bsf AppRurr goto LoqP

apDRuu

bcf

Lighlseek

bcf

r,ines€nsor

btsfEc

Objecls€nse

goto bsf

S+3 objectseuse

goto bcf

IJoop Objectsense

goto

IJooD

r.inesenEor LooI)

endllw btfaa goto

; Fu!.l Rang€ i ControL

i Reau[e r AOplication?

Enterch€ck

; Reslarl , ADplication?

Disable s€ehiag Disable g€trso!

Light liloale rJine

a i

,i*j

*?*

ToggLe Obj€ctsenge

:-.5

t Line g€n6or? I,inecheck t Stop Atry Plevious r ApDlication t Enable LighE t Seeking Moale t Disab].e objecE t S€eking uoal€ i Ena5le Line genaor

i:,-J

.:9

senaorch€ckl rnovf Pm.lcycL€,

Pll}l

Cycle

Sense? if unknown

i Disab Object uoale t s€eking

lJigbtseek

bsf gtoto

, Object i Retuln

t Enable object llofle ; seekiag

to objectsense

Loop

, t t t t t

MerruBtn. Bultoncdrpare llDPRun bcf

bcf

Fo:.warala

i Button i gtop Arry Plevious ,IDplication

LineCheck:

b€f

t ltoving

s1*

!4enuBtn,

bcf

100 mB

w

IJooD

& Right CbeckBulton9: r R€verao Bultoncdttr)er€ Buttong ' CheckvoLUp 2OO movln ; Rua for 200 ms llovecounte! mo'\^of novf NewPwMDutsY, !t PwuDuty novwf 0 bsf Dilection, t Movidg Back$tartla llurEleft bcf lUrnRight baf Plogram ApDRun bcf t Tura off Lightseek bcf t Eurn Off lJight t Seekiug goEo LooI)

Enterch€ck:

r Run for

to

w

0x03 STATus, z ObjSense

IJightsenae: incf

,fDCCycL€.

t

bcf

ADCCycle,

3

movf,

A.DCCycle,

w

btf,aE gotso movlw mo\rwf, baf,

STATgg, z A.DCCyclel b'00000001' A.DCON0 a.DCON0' GO

goto

lootr)

S e c t i o nT h i r t e e n Z i p Z a p s @R o b o t

? upalatse ADc? t Every 4lh Cyc].€

ADC , Run lhrough t Cycl€a i A.DcCYcIe = t (e.Dcqrc16 + 1) % 7

i Execut€ , Uachine

t Enable

ADC glate

:t!

'i| 1 :

;-.

LDC on RAO

, 3

ADC t Starl t ODeration

323

!!li

t i

hn

lLDccl,cIe]. xollw btfs8 golo rnovf goto

a tI I

Loop

3 ^ 2 STATUS, Z ADCCycLe4 e.DREgH, w

AItCCycle4: xorlw btfaa goto movlw moirwf baf goto

;

, i

Start

coodl Reafl

Gooal A.Dc Reaal, gave Ir€f! Valu€

A.DCValu€I.

4 ^ 3 STATus, z .B.DCcycIes b,00000101, A.DCONo ADCONo, cO

,

Enabl€

A.DC on RA1

ADC , Start , Op€ration

I.ooI)

.e.DCCycLe5. xorlw 5 ^ { btfss STATUS, Z golo aDcct'c1e6 tnovf ADRESII, w

ADCCycIe6: xorlw blfaa goto bsf

Badt alc t E.pect Value i Reaal, Ignole

Loop

6 ^ 5 gTATUg,

Z ADCCycLe? ADCONo, GO

i

.r$

ADCCycLeT: novf ADRESH, novwf goto ObjSeEae: movf

:,{

!t

r glart

eootl

Reaal

; Gooal ADC Reaal, Va1ue t Save Right

AIrcValueR lJoop

P$illcycl€,

w

anillw xorlw btfsa goco

0x03 1 STATSS, Z linesens€

cLrf

ObjFronlR

cllf cllf movf bsf movwf bcf bcf !!f movwf cllf bcf,

ObjFrontl ObjRear '!,r Obj ectPl{ll, S!!AmS. RPo PR2 ^ 0x80 STATUS, RPo STATUS, C Obj€ctPtcr4, w CCPR1L TIIRz PrRl, 1'!|R2IF

Ff

,.*.*

'J,, !d-r a"A ! -t

324

T2CON, TMR2ON

b8f bcf bcf,

STATug, RPo TRISC ^ 0x80, STASUS, RPo

t lPurn on a'ItIR2 for t objectE 5

, uDdla!€ object t se gor? r Every 4th Cycl.e

the , Cl€ar t Counters

;

setup

tIiIR2

Objects

PoRTC. 0 objFronlR, f PoRTC, 1 ObjFrontL, f PoR!!a, 3 f ObjRear, PrR1, !n4R2rF objloop

b6f baf

STATUS, RPo TRISC ^ 0x80,

bcf bcf

STATUS, RPo T2CON, TI|R2ON

bcf bcf bcf movLw

PFIonERIR PFrontr,rR PRearIR 30

subwf, blfsc bsf, movln aubwf btfac b3f movlw aubwf btfac b6f

ObjFrontR, !,r STATUS, C PFrontRIR 30 ObjElontl, w gtATus, c PFTonIIJIR 30 ObjRea!, w STATUS, c PR€ATIR

goto

lool)

PW!4CycIe,

5

Ptctil Outputs

Polllng

, ,

DiaabLe OutDu!

,

Tula

t

CLear Objec!

r Thirty t S€t,

PwM

off

IUR2

Tim€s

BiEa

f,o!

IJooD r Eitrisheal, r Aroundl Again

w

andlw xorlw btfsE golo

0x03 2 STATgg, Z oDeratinglogic

clrf

lJineFlontR

cllf trovf bgf movwf bef bcf fif rnovwf clrf bcf bsf

LineFronlL lin€PltlM, w STATUS, RPO PR2 ^ 0x80 STATUS, RPo STA!!US, C Lin€P$tl, w ccPRlL TMR2 PrR1, Tl'lR2IE T2CON, I'trlR2ON

bsf bcf bcf

STATUS, RPo TRISC ^ 0x80, sTATus, RPo

LineLoop: btsfEc incf btfsc incf btf6s

t Enal]le

t Loog Eere t objectsa

btfsc incf btfsc lncf btsfgc iacf btsfss goto

IJineSensa: r,ovf

3 t

:

baf

Obj Loop:

ADCCycle3: *lro!1!r btsfaa goto novf

goto

&rq

r B.pect Baat .e.DC i Reafl, Igrlole value

2 ^ L STATUS. Z ADccycLe3 A.DCONo, GO

.q.

F*-

1 STAfUS, Z Al)CCyc1e2 .eDRESll, nr

ADCCycle2: xorln blf,aB gotso bEf

nonwf

'*.-€

!

r upalate Line i Sedaora? t Evertr 4!h Cycle

, i

clear the Countsels

,

getuD

r Turn I.ine 4

t Enalcle

t Loop t Line PoRTc, 0 IrineFrontR, f PoRTC, 1 Lia€Flonll, f PIR1, ltrltR2lF

l , e 3 P I C @l ' C l l - JE x p e r i m e n t s f o n t h e E v i l

6enius

object

I'uR2

on TMR2 f,or

Pttu Output

He!€

Polling

gotso

IJinelJoop

bgf bsf bcf bcf

STATUS. RPO TRIsc ^ 0x80, { STATUS, RPo !2CON, T!|R2ON

bcf bef movlw

IJFToUtRIR IJFToatLIR 30

subwf btf,sc baf novlw Eublrf btfsc baf,

IJiDeFroutR, STATUS, C LFrontsRIR 30 lineFront!, STAfIUS, C LFronlLIR

gtoto

Loop

DisalcLe Turn

P9lM OutDut

off

T!lR2

clear

objecu

Thilly Set

Tines

Bits for

w

w

i i

Finiaheal, Loop Aroundl Again

ODeratsinglogic: IJogic Her6 (8 Per 32 **## - Put Opelating r cycleg) /Neeala set Plag i - Check "A99Reaet" Eo See if , **#* Application ia to be R€atartetl - Rdlote (!'tove or Stop) Direcl Control r **** ReaelE 'AppRunn Flag - Rdrole Control , **lt* aT.I "ADDReaetsT , #*## - Rdrot€ conurol "Reca11n gela

9roso

]JooD r Einisheat. t Alounal Again

Subloutineg t CoutrtLow: clrf Dlay CountsIJowlrooD: incf Dlay, f blfsc STATUS, Z goto CountlowDone soto $+1 gloto $+1 btfss RearIR goto Countlovrloop CounlLolrDo[e !

cllf

coutttsEighl,ooD : incf Dlay, f blfBc STATUS, Z goto CountHighDone goto s+1 goto s+1 btfac RearrR goto countEighloop countEighDone: novf Dlay, w subLw 35 btsfac sTATrts, c movllr aublrf

80 D1ay,

10 uE i counts, i! i Increments Low , Time signal t Clone Arounal? t Y€s, t Want

t Fini8heil,

i

Return

Gone Arountl?

t YeE, , Want

i

ReEurn Zero 10 Oycle IJooD

IJ€ss than

t Greate!

40?

than

79?

ro t Carry

eaal

Return Zero 10 Cycl€ Lop

in 10 us r Count, InclementE Eigh r Tirne Signal anat check

Dlay

I had a lot of trouble in this experiment(whichfigures,becauseit's the lastone) with the IR signalbeing too powerful. I was able to be successfulby carefully heatingthe heat-shrinktubing aroundthe bottompointingLED to the point wherevery little light was let out andwhite and black weredetected.Please checkthe CD-ROM and on my web page (www.myke.com) for updatedcodethat changesthe period PWM of the IR signalto decreasethe sensitivity of the line sensorsso they work better.Otherwise, you may wishto add a largepotentiometer(say10k) in seriesto seeif significantlyreducingthe current flowing throughthe IR LED helpsto better sensethe difference between white and black surfaces.

seh if

trYesn

i,1

l"t ;.{ t'ti i.-

1' I'.i *aj

For Consideration Whew!Although beinga lot of fun to work through, the ZipZaps hack wasa pretty intensive introduction to robotics.And a pretty goodintroductionat that.It is possiblehowever,that you might be questioningthis from a numberof perspectives, includingthe following: . .

The fragility of the robot The difficulty in addingthe new components precisely

. .

The ability of the robot to run only on flat, smoothsurfaces The apparentcomplexityof the software

.

What to do next

I like robotsthat are built like North Americancars built in the 1960s-ableto drive awayfrom a serious accidentwith nothingmore than chippedpaint.I am not trying to be facetious;chancesare your robot will drive itself off the tableyou are working on, andyou'll wishfor the samething.(Thisis a factor becausethere is no on/off switch due to my relying on the Zipzaps batteryfor power.)So rememberto chockthe wheels, andyou'll preventthe robot from goingoff on its own (it doesnot havethe power to successfully climb over at somepoint in time,you'll probaany obstacles).Yet, bly forget to do this and accidentallyleanon the remotecontrol.Despitethis dangerand a few broken wires when I was taking the PCB on and off the chassis,the robot held togetherdudng the development and during about 10 hoursof usewithout any problems.As a prototype,this robot is acceptablyrobust, but it is certainlynot sftongand resistantenoughto withstand the accidentsa commercial Droductwould needto withstand. This hackwould be much easierto perform if a custom PCB weredesisnedfor it. If surface-mount

5ectionThirteen Z i p Z a p s @R o b o t

325

frl

'J

technologywasused,then chancesare the custom PCB couldbe assmallasthe PCB that camewith the originalZipZaps (althoughsomekind of provision would haveto be madefor the IR TV remote-control receivers).The easeof buildingthe circuitrycould also be improvedby relocatingthe motor and steering driver transistorsfrom the cut-downZipZapsPCB to the robot PCB.I did not try this becauseI wantedto leavethe stockdriver circuitsintact,assumingthat they havebeenoptimizedfor the motorsand steering solenoidsused.A customPCB couldalsoreducethe fragility of the final robot. The car chassisand the all-or-nothingsteednglimit the surlaceson which it will run and how the robot works.I prefer working with differentiallydriven robotsthat canliterally turn on a dime.The very small turning radiusof the ZipZapschassisis aboutasgood asyou can expect,but still not asgood aswhat many robotsare capableof. Despitetheselimitations,the chassisandrobot are very usefulfor prototypingand shouldhelp you work throughthe sensorand software issuesof a larger,car-chassis-based robot. The softwareusedin this robot is not ascomplexas it looks.Hopefullyyou canseeitsprogression asyou work throughthe expedmentsand seehow relatively simplechangesresultin substantialimprovementsin capability.If I had presentedthe final softwarewithout any of the intermediatesteps,then I would agreeit is very complexfor somebodyto understandall at once. However,by goingthroughthe individualiterationsof the code,you shouldhavesomeappreciationof how complexsoftwareis built from a seriesof smallpieces. If you can't seeany way to usethis robot, then I suggestthat you spendsometime in your local library or bookstore,or on the Internet.Thereare literally thousandsof differentapplications(and methodsfor implementingthem in hardwareand software)that canbe usedasideasfor your robot.The Zipzaps robot will neverbring you a cold drink from your refrigerator, but it cansimulatethe actionsso you can createa larger,more capablerobot.Thereare alsomany

326

opportunitiesfor expandingthe capabilitiesof the robot,includingaddingmore or differentsensorsor evensomekind of object-capturehardware. On the positiveside,the robot is fast and tracksasif it were on rails.I would sayits speedand ability to movepreciselyis asgoodasor better than the odginal product.Although the car regularlyspinsout,this is not a desirabletrait in a robot.The extraweightof the prototypingPCB and the componentson it probably contdbutegreatlyto how the robot handles.I alsowas pleasantlypleasedby the batterylife of the final product;it seemsto be better than what the originalproduct had.This doesn'tseemquite possiblewhenyou considerthe variouselectricaldevicesaddedto the chassisaswell asits extraweight,which requiresmore power to move.It couldbe that the radio receiveruses a lot more powerthan the PIC MCU solution. Most important,this is a robot that you cando a lot with.The softwareis designedto make comingup with your own applicationcodeaseasyaspossible;the sensorsare continuallypolled by the basecodeand allow you lo simplyreadvariablesto find out the latestvalues.Similarly,to move the robot, it is simplya matter of writing to the appropriatemotor and steeringvariablesto affectany kind of movement.Finally,the remote-controlinterfaceallowsyou to initiate the operationof your codeand to stop it if it is not working properly.You canthen move the robot to a new locationto try something differentor in a newenvironment.It's actuallya nice basicrobot to experiment with. Like this book,the ZipZaps robothack shouldhave givenyou new insightsinto the PIC MCU, how it is interfaced,and how it is programmed.It is now up to you to take this knowledgeand go forward with your I'm looking forward to seeingwhat own experiments. you comeup with.And if at sometime the book's moniker appliesto you,and you usethe skills and knowledgegainedftom this book to take over the world,pleaserememberwherethoseskills andknowledsecamefrom.

l , a 3 P I C @l ' l C UE x o e r i m e n t s f o r

the Evil

6enius

tntrex

$,163 * (seemultiplication) + (seeaddition) - (seesubtraction) / (seadivision) ; (seesemicoloncharacter) & (AND),35 " (bitwiseXOR),35 = (equalssign),38,4G41 = = ( e q u a l tso s l a t e m e n t ) . 3 8 . 4 G 4 1 << (left shift operalor),L74 % (modulusoperator),34 -' (negation),35

I (oR),3s + + (unaryincrement)operator,48 I (bitwise[inclusive]OR),35 & (bitwiseAND), 35 - (bitwisenegation),35 ^ (bitwiseXOR),35 ! logicaloperator,35 [ ] (braces),39-40

A AC (alternatingcurrent),L54 accumulator,l64 Active Surplus,12 function) ADC function (seeanalog-to-digital addition(+): in assemblylanguage,1.6U1"69 assignmentstations,34 repeated,multiplicationas,280 addresses: language. 83.84 C programming for computed gotos,208 for memories,18 PICC Lite compiler,83,84 161-163 for programmemory(assembly), addressing: anay,73 assemblylanguage,173-175 bank (assemblylanguage),173-175 alphanumericLED displays,124 alternatingcurrent(AC), 154 AmericanNational StandardsInstitute(ANSI) standards,29

(ADC) function: analog-to-digiral for multiple devices,238-239 Ptc1.6F684,93-96 AND (&),35 AND gate,189-190 Animate icon,20 29 ANSI standards, application code,137-138,187(Seealso specific applications) applicationmainline/entryfunction (C), 82 applicationmainline/entrypoint (PICC Lite compiler),82 applications: linking multiple files into, 187 readability of, 67-68 tangiblereasonsfor, 89 architectures: computer,l8-19 PICl|'{{.CU,25-26 arithmeticoperations: basic,3,t-35 Boolean,35,36 order of, 3,t-35 with, 201-203 16-bitvalues/variables (Seealso specificoperations) T3 arrayaddressing, arraydimensions: 83 C programminglanguage, PICC Lite compiler,83 array variables,declarrng,182 arrays: (assembly),182-183 defining/implementing read-only (assembly),20&-210 ASCII bytes,convertingbyte into,289-291 T9 ASCII characters, ASCII dataformat,32 ASCIIZ srring,79,80,29+296 6, 159-185 assemblylanguageprograrnming, additioninstructions,168-169 file and basicdirectiveq160-161 asmTemplate.asm 173-175 bank addressing, ol 184 basicparts/sequence bit instructions,175-176 bit skip instructions"177-178 bitwiseinstructions,167-168 bu.bblesort,292-294 conditionalexecution,178-180

Index

327

assemblylanguageprogramrntng(Continuecl) converting byteq 289-291 decfszlooping, 180 definingvariables,165-167 defining/implementing arrays,182-183 division of 16-bit value by eight-bit vahte,28?-284 eighrbit multiplication with 16-bitprodtct,230-282 encrypting/decrlptingASClIZstring,294-296 even parity valuesfor bytes,29l-292 generatingFibonaccinumbersequence,297298 largest common factor of two eight-bit numbers, 298-300 loading/saving contentsof WREG,16+165 programmemoryaddresses, 161-163 sortinglist of 10 eight-bitvafues,292-294 squareroot of 16-bitnumber,28G288 squaringnumber using finite difference theory 28+286 strangesimulatorresults,170 subroutines, 181 subtraction instructionrlTl-t72 assemblylanguageresourceroutines,187-220 circularbuffen,212-213 conditional assembly,197-199 datastacks,210-212 defines,194-196 high-level programmng,Z\S-2j1 implementingC "switch" statement,191-194 implementingread-onlyarrays,208-210 logic simulation using PIC16F684,188-191 macroq 199-201 reading/r:r,ritingEEPROMdatarnemory,2l4-276 16-bitvalues/variables with arithmeticoperations, 201-203 universaldelaymacro,203-205 assignmentstatement n C,32-33 macro for,206-207

B

t tt /tt

s H

backdriving,3o5 bank addressing(assembly),173-175 basicarithmeticoperations,3,[-35 batteries,65 binaryformat.32 binarynumberoutput (with PICkitl start kit LEDs), 5G58 binary operators: C programminglanguage,84,85 PICC Lite compi1er,84,85 binary searchalgorithm,98 binary values,35-36 bipolar stepper motor control,765-268 bit instructions(assembly), 175-176 bit reset(bcf),175

328

bit set (bsf), 175 bir skip instuctions (assembly),177-178 bitwise instructions (assembly),167-168 bitwiseoperators(C),35-36 BOD circuit (seebrownout detect circuit) Boolean adthmetig 35,36 Boolean operationq bitwise, 167-168 BOR(seebrownoutreset) bottle-sort algorithm,292-294 braces({ }),39*40 breadboard wiring: BS2simulator,225 for dual seven-segment LED displaycircuit,lzz for AND gate,189 keypad-based BS2simulator,231 LCD1,777 for object detectionh^nging,Z4s for PIC MCU, 64-66 for potentiometerread circuit,110 sewo contol.2:72.273 for testing clocking optiong 107 for ZipZaps powersupply,306,308 breakstatement,44 breakpoints,20,22 bro$nout detect(BOD) circuit,91-93 brownoutreset(BOR),62,91-93 BS2 interface: commandssupportedby PIC16F684IRtag MCU,253 controlling multiple motors with PWM atd,264-265 keypad,23V23l and,servocontrol,ZT7-278 two-seworobot basewith,277-278 user,224-29 bubblesort,73-74,292-294 buffers, circular,2l2-213 built-in serialinterfaces(UARTs),222 button inputs: basic,58-59 debounci.ng,59-61 byte(s): converting into three decimal,two hex, or eight binaryASCII bytes,289-291. producingevenparity valuesfor,2gl-292

d \, C (seecarry) C programminglang1Jage,6,2:749 addresses, 83,84 applicationmainline/entryfunction,82 applicationsof,27 alnaydimensionq83 assignmentstatements,32-33 binary operators,84,85 bitwiseoperators,35-36

l , e 3 P f C @i l C U E x p e n i m e n t s f o n t h e E v i l

6enius

button read and LED output in,59 characterstrings,T9-81 complexstatements, 48-49 conditionalexecutionusingif statement,3g-41 conditionallooping,45-46 andconfigurationfusebits,82,83 constantformatting,31 32 constantvalues,71 constants,S4 dataaccesswith,27 datadeclarations, 83 datatypes,29 30 decisionstructures,84, 85 defines,Tl-72 definingfunctions,S2 directives,86 expressions, 33-35,84 functions,69-70 globalvariables,71, 83 goto Label statement,S5 implementingC switchstatementin assembly language,191-194 library functions,Sl 82 lists.76-78 local variables,7071,83 logicalexpressions, 37-39 looping,S5 macros,TlJ2 mathematicaloperators,s4 microcontrollerapplicationsin,137158 model railwayswitchcontrol,153-155 nestedconditionalstatements,4l+3 null statement,4S-49 PC operatingstatusdisplay,15G158 PIC MCU "piano,"151-153 pointers,27,7G78,83 PumpkinLED display,138140 reaction-timetester,140-142 and readabilityof programs,68 return statement,36 Rokenbok@monorail/trafficlights,143-146 seven-segment LED thermometer,146-150 singledimensionalarrays,83 for statement,46-49 strings,S3 structures, 75-76 subroutines,6g switchdecisionstatement,43-44 switchstatement,85 unions,76 values,83 variablearrays,7374 variabledeclarationstatements,28-29 variabletypes,84 CadmiumSulfile(CDS) cells,238 call instruction,l62 cannedoscillators,10G108

carry (C), 168,169,171 casestatement,44 cblockdirective,161,,766,1"67,201, CCP: generatingPWM signalsusingTMR2 and,111-114 I/O pin resistancemeasurements using,109-111 CCP PWM, DC motor driven usingpotentiometer control and,257-260 112,113 CCP1RLregister, CD-ROMs (in starterkit), 1 CDS (CadmiumSulfile)cells,238 cFlash.c: simulating,in MPLAB IDE.20-24 wiring circuit,65-66 chardata type,33 charunsignedvariables,188 characterstrings: C programminglanguage, T9 81 encrypting/decrypting, with substitutionalgorithm, 29+296 circularbuffers,212213 clearthe WatchdogTimer (clrwdt) instruction,188 clippedsignal,235,236 clocks: comparingoscillators,106-109 andfunctionsin instructioncycle,203 PIC16F684,16 resistor-capacitor, 95 (Seea/sotimers) clrwdtinstruction,188 code,formatting,68 coi1,255,256 comments,31,68, 160 commoncathode/anode configuration,120 commonfactor of two eight-bitnumbers,298-300 commonregisters,173 comparators: for IR surfacesensor,240,241PIC16F684, 96-99 comparingclock oscillators,106-109 completeresetsolution(PIC16F684),62 34,36 complexexpressions, computedgoto,208 computers: architectures, 18-19 127 asrandomnumbergenerators, conditionalassembly: assemblylanguageresourceroutines,197-199 macrousing,20G-201 conditionalexecutionstatement: assemblylanguage,178-180 nested(C), 41-43 usingif statement(C), 39-41 with,202 conditionaljumps,16-bitvalues/variables conditionallogic,operatorsfor,36 conditionallooping(q,a5a6 _CONFIG directive,l-61-,205

Index

329

l,-l t4 ,.- , {'t :.i.j

configuration fuse bits: and C programminglanguage,82,83 parameterspecifications, 17 PICC Lite compiler,82,83 and unwanted functions, 100 configurationword (PIC16F684),1G17 constantformatting (C)3\a2 constantvalues(C programminglanguage),71 constants: C programming language,84 PICC Lite compiler,84 contextregisterq134 conventions,1.1 counterg29,57 for longer delays,203-204 program,162 sweepgenerator,94 crysral(PIC16F684),108 Cygwin,157,158

D

M t2i

{)

d H

data,storing(seestoringdata) data access(C),27 datadeclarations: C programming language,83 PICC Lite cornpiler,83 data encr)?tionstandard(DES),294 data segments, 19 data sizeq32 data stacks,210-212 data types,29-30 (Seealso spectfictypes) DC (seedigit carry) DC motor control,255-256 with simpleTMR0 PW\11,261-263 usingCCP PWM andpotentiometercontrol, 257-260 deadtime executioncycles,137-138 debouncing: button inputs,59-61 multiple microswitch,237-238 Debtgger,2I,24 debugging: in assemblylanguage,159 difficulties with, 36 pointersin,77 decfszlooping, 180 decirnal,convertingbyte valueinto,289,291 decimalformat,32 decisionstatements,switch (C), 43-44 decisionstructures: C programminglanguage.84. 85 PICC Lite compiler,84,85 declarationstatement: for functions,69 macrog199

330

declaringvariables: anay,187 in assemblylangua9e,765,166 and computer architecture,19 in PICC Lite compiler,28 definelabel,71, 72 defines: assemblylanguage,194-196 C programming language,71-:72 conditional assembly,197 definingarays (assembly),182-183 defining functions: C programming language,82 PICC Lite compiler,82 definingvariables(assembly),165-167 delays: long timer delaysusingTMR1, 10+105 PIC MCU,53-54 shorttimer delaysusingTMRO,101-102 universal delay maqo,203-205 DES (dataencryptionstandard),294 developmentPC,interface to, 13 Digi-Key, 12 digit carry (DC), 16UL69, 17L digital logic,117-119 digital multimeter(DMM), 134 digital thermometer, 14G1-50 digitally proportional signal,272 DIP sockets,51 direct load (movf) instruction, 164 directives: assemblylanguage,16L-1-63 C programming language,86 PICC Lite compiler,86 (Seealso specificdirectives) disassembly listing,190,191 distance-range sensors: IR object-rangingsensor,247249 ultrasonic,249-250 division(/): of 16-bitvalueby eighrbit value,282-284 assignment stations,34 asrepeatedsubtraction,282,283 DMM (digitalmultimeter),134 do-it-yourselfIR objectsensors, Z3-246 dot-matrixLED displays(LED matrix), 124 double float (floating point) variables typeE30 do/untilstatement,46 dual in-line chip package(DIP) socketq51 duty cycle,111

E ECC (error detection/correctcodes),292 ECCP module (seeEnhanced Capture/Compare/PWM module)

l , e 3 P I C @l t C U E x p e r i m e n t s f o n t h e E v i l

6enius

EEPROM memory(seeelectricallyerasable programmableread-onlymemory) EEPROM read,214 EEPROM write,21+216 eighlbit numbers: eight-bitmultiplicationwith 16-bitproduct,28G-282 largestcommonfactor of two, 298-300 eightbit values/variables: bubble-sortinglist of,292-294 divisionof 16-bitvalueby,282 284 saving16-bitvaluesas,32 electretmicrophone,235 electricallyerasableprogrammableread-only (EEPROM) memory,19 reading/writing(assemblylanguage),214-216 storinghetrievingdatawith,114-115 emulators.24.25 ASCIIZ string,29,l 296 encrypting/decrypting ENDC directive, 161 endingapplications(PIC MCU), 63-64 EnhancedCaptureiCompare/PWM(ECCP) module,104 Capturemodeol110-111 PWM generatorfunctionin, 111-114 equals(: ) sign,38,40-41 equalsto (= =) statement,38,4041 equate(equ) directive,166 error detection/correct codes(ECC),292 evenparity values,for bytes,291292 execution: assemblylanguage,178-180 conditional,lTS-l8o expressionstatement,32 Cprogramminglanguage,33-35,37-39,84 logical,37-39 (PICC Lite compiler),84 expressions

E' fanout,118 Fibonaccinumbersequence,generating,29T-298 file narnes,67 file registers,19,164 fill areas(PCB),265 finite differencetheory,squaringnumberusing, 284 286 first,outside,inside,last(FOIL), 281 flag variableq29,30 Flash.c: Build Information for,7 loading,6 250 flight time (ultrasonicsignals),249, float (floatingpoint) variablestypes,30 floating-pointoperations,149-150 floodareas(PCB),265 FOIL (first,outside,inside,last),281

folders,6T for statement: C prograrnminglanguage,46-49 in cFlash.csimulation,2l formattingcode,rulesfor, 68 full H-bridgecircuit,256:258 full stepping,266 full-bridgeoutput forward mode (PWM generator), 113,714 functions C programminglanguage,69-70 declarationstatementfor,69 defining,PICC Lite compiler,82 defining(C),82 recursive,70,297 unwanted,100 written asmacros,200 (SeealsospeciJic lunctions)

G globalinterruptenable(GIE) bit,135 globalvariables(C),71,83 goto instruction,162,208 goto Label statement: C programminglanguage,S5 PICC Lite compiler,85 graphicLCDs,126

H halfadder,291,292 half H-bridgecircuir,256,257 half stepping,266 Harvard architecture,18 19,208 H-bridgecircuits,256,257 for dual DC motor,264 tl.256-258 ha1f,256,257 headerblock,6T-68 hex files,19 convertingbyte valueinto,289291 hexadecimal, hexadecimalformat,32 HIGH directive,201-202 highJevelprogramming: in assembler,205-207,279 assemblylanguagevs.,159-160 HT:Soft PICC Lite compiler,1 4,6,7 83,84 addresses, advantages of,28 applicationmainline/entrypoint,82 array dimensions,83 assemblylanguagecodefor,187-188 binaryoperators,S4,85 capabilitiesof,28

Index

331

.. .

III-Soft PICC Lite compiler (Continued) codeproducedby,28 configuration fuse bits, 82,83 constants, 84 data declarations, 83 data types,29-30 decisionstructures,84,85 declaringvariables,28 defining functiong 82 diectives, 86 downloading/installing,2-4 expressions,84 floating-point capabilities ol 288 goto Inbel statement,85 interrupts,135-136 library functiong 8G88 looping,85 macroq 87-38 mathematicaloperators,84 MPLAB IDE integrationwith, 28 pointers,83 pragmaoptions,86 return statement,86 singledimensional arrays,83 specifying,6 stringq 83 switchstatement,85 variabletypes,84 variablesinsidefunctions,83 while loop,46 HT-Soft web site,2

I

X (, €

c

H

ICE (in-circuitemulator),25 icons,10-11 IE (interrupt enable),135 IF (inlerruptrequestflag)bits.135 if directive, 197 if statementfor conditionalexecution(C),3941 immediate load (movlw) instruction, 164 immediate values/numbers,162 implementingarrays(assembly),182-183 incfsz instruction, 180 in-circuit emulator (ICE), 25 includedirective,161 indexregister,182 indexedaddressing, 73,182 lnouctor (collJ.z)), z)o infrared(IR) remotecontrol: for object detection,243-246 f or ZipZaps@rob ot, 37U317, 31G377 infrared(IR) sensors: do-it-yourself object sensorq243-246 line-following (ZipZaps@rob ot), 32(1325

332

objecfdetection(ZipZaps@ robot), 318-319 object-ranging sensor,247249 robot IR tag,251-253 surfacesensors,239-241 input mode (I/O pn),14,33 input/output (I/O) pins: allocationof,230 functions ol 14 and LEDs, 13

Prc16F684, 14-16 resistancemeasurements usingCCP,109-111 sharing,230 instruction cycleg21 instructions,160,216-218 instrumentinterface (PlC MCU ), 23L-234 int dataR?e,29,30 interfaces,119-136 debugger,25 driving seven-segmentLED display directly from Prc1.6F684,1L9-rZ1 instrument,PIC MCU,237-234 keypad,PIC MCU BS}Z3VZ37 LCD display,12L128 LED matrix displays,724-176 multiple seven-segment LED displays,121-123 of PICkitrM 1 starter kit to PC, 13 producingrandomnumbers,128-129 sensor,222 SharpGP2D120rangingobject sensorE242-243 switchmatrix keypadmapping,131-134 two-bit LCD display,729-730 user,PIC MCU 852,22+229 interrupt enable(IE), 135 inteffupt requestflag (IF) bits,135 interruprs,101,134-136,239-241I/O pins (seeinput/output pins) IR opto-interrupters,239-24t IR remote control (seeinfrared remote control) IR sensors(seeinfrared sensors) IR switchOpro-NPN,240

J Jameco,I2 jumpEconditional,202

K k (thousands),11 keypad: BSZ interface,23F231. switchmatrix keypadmapping,131-134 Kirchoffs Law, 154

l , e 3 P I C @l ' C l l - JE x o e r i m e n t s f o r

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6enius

L labels, 16,162 addressvaluestbr, 162-163 for conligurationword bit, 16 declaredwith variabledirective,198 numericvalueassociated with,71 lastin lirst out (LIFO) memory,2l LCDs (seeliquid crystaldisplays) LDRs (seelight dependentresistors) LED matrix displays,I24126 LEDs (seelight-emittingdiodes) left shiftoperator(<<),174 LFSRs(seelinear feedbackshift registers) libraries: C run{ime, 81 and data types,30 library functions: C p r o g r a m m i nl ag n g u a g e . 88li PICC Lite compiler,8G88 L I F O ( l a s li n f i r s to u t )m e m o r l2. I light dependentresistors(LDRs), 143,1421 for light sensors, 238-239 ZipZapsrobot,317-318 light following (ZipZaps@ robot),318 light sensorq238-239,317-318 light-emitting diodes(LEDS),1,2 alphanumericLED displays,124 binary numberoutput using,56'58 driving seven-segment displaydirectlyfrom PIC16F684, 119-121 LED matix displays,12+126 multipleseven-segment displays, 121-123 organizationol, 13-14 PC operatingstatusdisplay,156 158 Pumpkin LED display,138-140 sequencing, 55-57 seven-segment LED thennometer,146-150 simpleprogramto flash,58 limit checking,2ll linear teedbackshift rcgisters(LFSRs),138-40 line-followingsensors, IR (ZipZapsltrobot),320-325 Linux, 1 liquidcrystaldisplays(LCDs),120,12G130 list directive,160-161,220 lists(c), 76-78 literal values/numberq 162 littleendian,201 (C),70 71,83 localvariables logarithmfunction,150 logic: conditional,36 digital,117 119 simulation, usingPIC16F684, 188 191 (C),37 j9 logicalexpressions

logicaloperator(!), 35 longtimerdelaysusingTMR1, 104-105 loop incrementstatements, 46 loop testexpression, 46 looping: C programminglanguage, 85 conditional(C),45 46 decfsz(assemblylanguage),180 PICC Lite compiler,85 relativeaddressfor,203 TMR1 vs.for loop,105 LOW directive,201-202 L293D chrp.264265

M M (millions),l1 11 F (millionths), m (thousandths), 11 machinedreceptaclesocket,51 maclos: assemblylanguage,199-201 tbr assignment statements,20620l C programminglang\age,7LJz OPERATE,2O5 207 PICC Lite compiler,87-88 TimeCheck,316 universaldelay,203205 usesof, 199-200 mapping,switchmatrix keypad,131-134 mathematicaloperators: C programminglanguage, 84 floating-pointoperations,149 150 PICC Lite compiler,84 matrix LED displays,12+126 MAX 756step-uppower supply,305306 _MCLR operation(PIC MCU), 61-63 MCU (seemicrocontroller) measurements, 11 memory: EEPROM,1t4-115 LIFO, 210 PIC MCUs,25 PIC16F684,18 19 program,addresses for, 161-163 memoryspace,18 metricsystem,11 MicrochipPIC@microcontrollers(PIC MCUs), 1-12 basicbuttoninputs,5859 basicdelaysapplication,53-54 binarynumberoutput usingPlckit 1 starterkit LEDs,5G58 BS2 keypadinterface,230231 BS2userinterlace,22+229 configurationparametersof, 16

Index

333

Microchip PIC@microcontrollers(Conrlnaed) configuring,6 debouncingbutton inputs,59-61 electronicsPCB (ZipZapsorrobot),307-309 endingapplications,63-64 familiesof, 25 instrumentinterface,237-234 _MCLR operation,6l 63 parameterwords,16 pafi numbersfor,2+25 partsrequiredfor wiring on breadboard,64-66 PCsvs.,18 "piano,"151-153 PIC12F675,1, 10 PICI6F684(seePIC16F684) power supply(ZipZaps@ robot),305-306 recommendations for,26 sequencing PICkit 1 starterkit LEDS,55-56 turning off power,14 wiring cFlash.ccircuit,65-66 MicrochipPICkitrM1 starterkit,1+,10,11 binarynumberoutput usingLEDs,56-58 contentsol 1-2 icon for, 11 machinedreceptaclesocketmodification,51 ordering,1 organizationof LEDs, 13-14 PC interface,13 potentiallynegativeissueswith,13-14 sequencingLEDs,55-56 simpleLED flashapplication,5 8 testcircuit,13 turning off power,4 USB port liability,4 ZIF socketaddition,5l-53 Microchipweb site,4 1l,137-158 (MCU), microcontroller MicrosoltWindows,1, 11 microswitchdebouncing,multiple,23T-238 millions (M), 11 millionths(pt),11 model railwayswitchcontrol,153-155 modulus(%) operator,34 monorail,Rokenbokcr, 143-146 motor control,255 278 bipolarsteppermotorcontrol,265-268 controllingmultiple motorswith PWM and BS2 rnterface,264-765 DC motor controlwith simpleTMR0 PWM, 267263 DC motor driven usingCCP PWM and potentiometercon1rol,257-260 multiple servocontrol softwarestructure,Z74276 radio-controlmodelservoco\tro1,272274 two-seNorobotbasewithBS2interface,zTT-z18 unipolarsteppermotor control,269 271 ZipZaps@robot,3lL131.2

334

MouserElectronics,l2 MPASM@, 159,161-163 conditionalassemblydirectivesin, 197 directives,216,218-220 macros,199 MPLAB@integrateddevelopmentenvironment (IDE),1--:7,9-I2 asdevelopmenttoo1,279 downloading/installing,4,5 screenshotsof, 11-12 simpleprogramto flashLED,5-8 simulatingcFlash.c,20-24 simulatortool,10,70-71 sourcecodecompilingby,187 tutorial for, 2 upgradesol 1 verslonsof,12 multidimensionalarrays,74 multiple assignment statement,33,35 multiplemicroswitchdebouncing,23T-238 multiple servocontrolsoftwarestructve,214 276 multiplication(x): assignment stations,34 eight-bit,with 16-bitproduct,280-282 asrepeatedaddition,280

N names,variable,29 naturallogarithm,150 negation(-),35 nestedconditionalstatement(C), 41 43 nestedsubroutines, Tl Newton'smethodof zero finding,287 non-return-to-zero(NRZ) protocol22\223 nonvolatilememory,114 NOP0; statement,53-54,60,188 nopstring,161 NRZ protocol(seenon-return-to-zeroprotocol) null statement,32,48-49 numbers: ASCII valuesas,289 eight-bit,findinglargestcommonfactorof,298-300 eight-bitmultiplicationwith 16-bitproduct,280-282 generatingFibonaccinumbersequence,29T29S immediate/literal, 162 16-bit,finding squareroot of,28G288 squaring,usingfinite differencetheory,284286

n \-' objectsensors: do-it-yourself,243-246 interfacingto SharpGP2D120,242243 IR object-rangingsensor,247-249

l , a l P I C @l l C U E x o e r i m e n t s f o r

the Evil

Genius

ultrasonicdistance-rangesensor,249-250 ZipZapsorobot,318-319 Ohm'sLaw,154 one-timeprogrammable(OTP) parts,197 Ontario Ministry of EducalionCurriculum Guidelines for ComputerEngineering,9 op-ampcircuit,235 open-collectoroutput,119 open-drain output,11g OPERATE macro,205-207 operatingstatusdisplay(PCs),15G158 OperationResult,168 operational-amplifier(op-amp)circuit,235 OPT (onetime programmable)parts,197 OPTION rcgister,101 opto-interrupters, 239-241 OR (l) operator,35 order of operations,34-35 org directive,161 oscillators,clock,10G109 output controller,ll2 output mode (I/O pin), 14 output sink currents,118

p p (trillionths),11 pagesize(programmemory),163 ParallaxBASIC Stamp,100 parameterstrings,Tl parameterwords,16 parasiticpower,66 parity values(for bytes),29l292 part numbers,24-25, 197 PartsBin icon,11 partssuppliers,12,240 PCB (seeprinted circuit board) PCL register,208,209 PCLATH register,208,209 PCs: operatingstatusdisplay,156-158 PIC MCUs vs.,18 PC/Simulatoricon,11 phototransistors(PTs),240,247 "piano,"PIC MCU, 151-153 PICMCUs(seeMicrochipPIC@microcontrollers) PIC12F675,1,10 PIC16F684,1,10, i3-26 ADC function,93 96 architecture0126 brownoutreset,62,91-93 builtin functions,8990 built-in hardwarefeatureE90 comparatoroperation,9G99 compadngclock oscillators,10G109 completeresetsolutionfor,62

configurationword,16-17 damagefrom plugging/unplugging, 14 driving seven-segment LED displaydirectlyfrom, 119-12I generatingPWM signalsusingCCP andTMR2, 111 114 I/O pins,14-16 logic simulationusing,188-191 longtimerdelaysusingTMR1,10,+ 105 short timer delaysusingTMRO,101-102 simulatingcFlash.cin MPLAB IDE, 20-24 stodng/retrievingdata usingEEPROM memory 11+115 timed I/O pin resistancemeasurements usingCCP, 109-111 TMR0 prescaler,102-103 variablememory/registers/program memory,1s 19 watchdogtimer,99 100 PICC Lite compiler(s??HT-SoftPICC Lite compiler) PICkitrMl starterkit (seeMicrochipPICkitrM1 starterkit) pin throughhole (PTH) chips,65 polnters: andASCII strings,T9 C programrninglanguage, T6 7{i,83 ICC Lite compiler,83 Polaroid6500ultrasonicranger,249-250 pollingintervals,222 PORT bit, 1,+16 positiveactiveread,negativeactivewrite (R/W), 127 pot read,110 potentiometer,25T-260 power: AC, 154 with batteries,65 parasitic,66 turning off,14 for ZrpZapsrobot 305-306 pragmaoptions(PICC Lire compiler),86 preprocessor, Tl prescaler,TMRo,102 103 PrimeCheckfunction,T0 Princetonarchitecture,18,19 printed circuitboard (PCB),1,2 fill/flood areason,265 ZipZaps@,304,307-309,372 problems,resourcesfor, 300 programcounter,162 programfiles,lg programmemory,18 pagesizeol 163 specifyingaddresses for (assembly),161 163 programmerPCB,1,2 programminglangLrages,zT (Seealsospecifrc languages) programmingproblems,resourcesfor,300

Index

33s

PTH (pin throughhole)chips,65 PTs(seephototransistors) pulsewidthmodulation(PWM): DC motor controlwith CCP PWM and potentiometer,25T-260 DC motor control with simpleTMROPWM, 267-263 generatingsignalsusingCCP andTMR2,7|7-774 for motor-speedcontrol,256 multiplemotorscontrolwith BS2interfaceand, 264-265 PumpkinLED display,138-140 PWM (seepulsewidth modulation)

O E quotient,282,284

E r\ Radio Shack,12,302 radio-controlmodelservoconftol,272-274 randomnumbers,producing,128 129 rangingobjectsensors, interfacingto,242-243 RC clock,95 RC oscillator,107,108 rctimefunction,109,110 reaction-timetester,I40-1-42 readabilityof programs,31,67-68,159 readingEEPROM datamemory,21+216 read-onlyarrays(assemblylanguage) .208-270 real-timeclock (RTC) variable,316 recursivefunctions,70,297 recursivesubroutine,181 reglsten: accessing,33 banksof 173-175 CCP1RL,112,113 common,173 context,l34 index,182 involvedwith ADC,94-95 LFSRs,138-40 monitoringvaluesof,21,2324 OPTION,101 PCL,208,209 PCLATH,208,209 PIC16F684,18,19 shadowed,173 STATUS,164,168-L69,173-175,177 T1CON,104 WREG (assemblylanguage),164-165 remainder(division).282,284 remotecontrol:

336

IR, ZipZaps@ robot,310-311,31G317 TV receiverfor object detectron,243244 RequiredPartsicon,10-11 requirementcontinuum,280 reset: address(assemblylanguage),161 bits indicatingreasonsfor,63 -MCLR operation,61-63 PIC76F684,62.9L-93 WDT, 100 Reseticon.20 resistance: in DC motors,255 I/O pin, measurements usingCCR 109-111 thermistor. 148-.149 (RC) clock,95 resistor-capacitor (RC) oscillator,107,108 resistor/capacitor resistors: light-dependant, 143,144 single-inlinepackage,139 resonator(PIC16F684),108 retrievingdata (EEPROM memory),114-115 retum statement(PICC Lite compiler),86 robots: IR tag,251-253 radio-controlmodel seryoconftol,272-274 two-servorobot basewith BS2interface,277278 (SeealsoZipZaps@-based robots) Rokenbok@ monoraiVrrafficlights,143-146 RTC (real-timeclock) variable.316 run arroq 20 Run icon,20 21 RJW (positiveactiveread,negativeactivewrite),127

s segments,l8 (BASIC).44 selectstatement self-contained operutron,Zl4 semicolon(;) character,32,68,160 sensingoperations(polling),222 sensors,221-253 do-ityourself IR objectsensors,243-246 environmentalparameterswith,222 interfacingto SharpGP2D120rangingobject sensors,242243 IR objectrangingsensor,247249 IR surfacesensors.239-241 light,238-239 line-following(ZipZaps@ robot),320-325 multiple microswitchdebouncing,23T238 (ZipZaps@ robot),318-319 object-detection PIC MCU BS2keypadinterface,230-231 PIC MCU BS2userinterface,224229 PIC MCU instrumentintedace.23l-234

l , P 3 P I C @1 1 ( l JE x p e r i m e n t s f o r

the Evil

6enius

polling intervals for, 222 robot IR tag,251-253 sounddetection,235-237 ultrasonic distance-rangesensor,249-250 sequencingPICkit 1 starter kit LEDS, 55-57 servocontrol: multiple servo control software structve,2iT4-276 radio-control mod el,2l72-274 two-servorobot basewith BS2 interface,2iT7-278 seven-segment LED displays: driving directlyfrom PIC16F684,119-121 multiple,121-123 thermometer,146-150 SFRs (seespecialfunction registers) shadowedregisters,173 SharpGP2D120rangingobjectsensorS242-243 short timer delaysusingTMRO (PIC16F684),L07-102 SI (SystemInternationale),11 simulation: BS2 interface,22+229 of cFlash.cin MPL AB LDF,,2U24 logic simulationusingPIC16F684,188-191 prior to burning prograrns,20 simulators: MPLAB IDE, 10,7V71.,170 sendingservopositiondatafrom,278 strangeresultswith, 170 singledimensionalarrays: C programming language,83 PICC Lite compiler,83 singleequals(:) sign,38,4G41 single-dimensional arrayq73J 4 single-inlinepackage(SIP) resistor,139 single-outputmode (PWM generator),114 singly linked lists,7H8 SIP (single-inlinepackage)resistor,139 16-bitnumber,finding squareroot ol28G288 16-bitvalues/variables: with arithmetic operations,201-203 division of by eight-bit value,282-204 int data type,30 programming flexibility with, 201 savingin eight-bit variables,32 sleepstatement,100 slottedIR opto-interruptery240 SMT (surface-mounttechnology),304 sobrietytester,140-142 sound input recognltlon, 235237 sourcecode,1 specialfunctionregisters(SFRs),19,164 spoolingfunction,210 squareroot of 16-bitnumber,finding,28G288 squaringnumber usingfinite differencetheory,284-286 stackmemories,18 stacks,data,Z1U212 StandardC values,29

state machine,95 STATUSregister,164 and additioninstructions,168-169 and bank addressin 9,173-175 andbit skip instructions,177 steeringcontrol (ZipZaps@ robot),311-312 StepIn icon,20 StepOut icon,20 StepOver icon,20 steppermotor control: bipolar,265-268 unipolar,269271 steppermotors,266 step-uppower supply,305 stimulusfunction,20,61 Stimuluswindow,61 Stopwatchfunction,20,23,54 storingdata: ctctular bfifer,27311-4 dat^ stacks,27}-ZIz usingEEPROM memory(assembly), 214-216 usingEEPROM mernory(C), 11,t-115 strings: C programming language,83 character(C),79-81 labels,162 PICC Lite compiler,83 structlanguagestatement,75 structures(C),75-76 subroutines: assemblylanguage,161,181 C programminglanguage,69 nested,71 wdtten asmacros,200 substitution algorithm, encrypting/decrypting ASCIIZ string with, 29+296 subtraction( -): in assemblylanguage,777-772 assignmentstations,34 repeated,divisionas,282,283 Suprernetronic, 12 surface-mounttechnology(SMT), 304 sweepgenerator,94 switchcontrol (modelrailway),153-155 switchmatrix keypad,mapping,131-134 switchstatement: C programming lan guage,4344, 85 C switch statement in assemblylanguage,IgT-7g4 PICC Lite cornpiler, 85 SystemInternationale(SI), 11

T Tab ElectronicsBuild Your Own Robot Kit, 301-302 Thb Electronics Sumo-Bot, 25I-253, 307-i02

Index

337

,{ !-{

ptu

X

task-controlsoftware(Zipzaps@robot),313-316 Templatefile,160-161 testcircuit (PICkitrM1 starterkit), 13 thermistors,148-149 thermometer,seven-segment LED, 14G150 (k), 11 thousands thousandths(m), 11 TimeCheckmacro,316 timed I/O pin resistancemeasurements usingCCP, 109111 timers(TMR): DC motor control with simpleTMR0 PWM, 26L-263 generatingPWM signalsusingCCP andTMR2, 1.L7-11.4 long timer delaysusingTMR1, 104 105 prescaler, TMRO,102-103 short timer delaysusingTMRO,101-102 Watchdog, 16,99-100 title directive,160 TMRs (seetimers) Toolboxicon,11 totempoleoutput,118,119 traffic lights,Rokenbok@, 143-146 translstors: in DC motor control,258,260 phototransistors, 240,241 translationvoltage,189 trillionths (p), 11 TRIS (Tii-State)bit, 1,116 tri-stateddver output,119 TV remotecontrols: for objectdetection,243244 for ZipZaps@ robot, 310-311,316-317 two-seryorobot basewith BS2interface,277278

U UARTs,222 ultrasonicdistance-range sensor,249-250 unaryincrement(+ +) operator,46 union statement,T6 unions(C),76 unipolarsteppermotor coni.lol,269-21 1 UniversalAssemblyLanguage,27 universaldelaymacro,203-205 u n i v e r s a l s e rbi auls( U S B )c a b l eI. universalserialbus (USB) port, 13,14 UpperCasemacro,72 USB cable,1 USB port,13,14 userinterface(PICMCU BSZ),224229

338

v Valuevariable,5T58 values: array,208 ASCII,289 binary,35 36 C programminglanguage,83 for complexexpressions, 36 for configurationword, 16 constant,Tl converting,289-291 immediate/literal,162 in programcounter,162 of re gisters,2l-,23-24 in unions,76 of vartables.21-,23-24 variablearrays(C),73-74 variabledeclarationstatement,165 C programming language,28-29 and computerarchitecture,19 variablememory,18,19 variabletypes(PICC Lite compiler),84 variables: binary,35-36 T0-71,83,84 C programminglanguage, charunsigned,188 declaring(assemblylanguage),165,166 declaring(C),19,28 defining(assemblylanguage),165-167 global,71,83 local,TG-71,83 locationof,19 monitoringvaluesof.21-,23-24 naming,29 pointers,7G78 variablesinsidefunctions(PICC Lite compiler),83 #v(expr)directive,198-199 von Neumannarchitecture,18,208 Vrei 97-98

v{ Watchwindow,23,24 watchdogTimer (WDT): disabling,16 PIC16F684,99-100 WDT (seewatchdogTirner) while directive,198 while loop,45-46 Windows,1,11

l - JE x o e r i m e n t s f o r l,a3 PICo l'lC

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working register (WREG): in addition instructions,168-169 in bitwise operations,167-168 loading 164-165 read-only array element,208 savingcontents of, 165 and subtract instructions,77I, 772 writing EEPROM data memory,2L4-216

tt

J}

xoR ("),3s

H

s

p p

zero check module, 164 zero insertionforce (ZIF) socket,14,51-53 ZipZaps@-based robots,301-326 basic task-control software,31!316 characterizing,303-304 IR line-following sensory320-325 IR object-detectionsensors, 318-319 IR remote control,376-377 IR TV remotecontrol,310-311 light sensorsand light foUowing,317-318 motor and steering control, 311-312 PIC MCU electronicsPCB,307-309 PIC MCU power supply,305-306

lndex

o

x

339

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