Appendix A_ Programming a Microcontroller - Book_ PIC Microcontrollers

8/27/2014 Appendix A: Programming a Microcontroller - Book: PIC Microcontrollers

http://www.mikroe.com/chapters/view/11/appendix-a-programming-a-microcontroller/ 1/17

TOC Introduction Ch. 1 Ch. 2 Ch. 3 Ch 4. Ch. 5 Ch. 6 Ch. 7 Ch. 8 Ch. 9 App. A App. B App. C

Book:PICMicrocontrollers

AppendixA:ProgrammingaMicrocontroller

MicrocontrollersandhumanscommunicatethroughthemediumoftheprogramminglanguagecalledAssemblylanguage.ThewordAssembleritselfdoesnothaveanydeepermeaning,itcorrespondstothenamesofotherlanguagessuchasEnglishorFrench.Moreprecisely,assemblylanguageisonlyapassingsolution.Inorderthatthemicrocontrollercanunderstandaprogramwritteninassemblylanguage,itmustbecompiledintoalanguageofzerosandones.AssemblylanguageandAssemblerdonothavethesamemeaning.Thefirstonereferstothesetofrulesusedforwritingprogramforthemicrocontroller,whilethelaterreferstoaprogramonapersonalcomputerusedtotranslateassemblylanguagestatementsintothelanguageofzerosandones.AcompiledprogramisalsocalledMachineCode.A"Program"isadatafilestoredonacomputerharddisc(orinmemoryofthemicrocontroller,ifloaded)andwrittenaccordingtotherulesofassemblyorsomeotherprogramminglanguage.Assemblylanguageisunderstandableforhumansbecauseitconsistsofmeaningfulwordsandsymbolsofthealphabet.Letustake,forexamplethecommand"RETURN"whichis,asitsnameindicates,usedtoreturnthemicrocontrollerfromasubroutine.Inmachinecode,thesamecommandisrepresentedbya14bitarrayofzerosandonesunderstandablebythemicrocontroller.Allassemblylanguagecommandsaresimilarlycompiledintothecorrespondingarrayofzerosandones.Adatafileusedforstoringcompiledprogramiscalledan"executivefile",i.e."HEXdatafile".Thenamecomesfromthehexadecimalpresentationofadatafileandhasasuffixof"hex"aswell,forexample"probe.hex".Afterhasbeengenerated,thedatafileisloadedintothemicrocontrollerusingaprogrammer.Assemblylanguageprogramsmaybewritteninanyprogramfortextprocessing(editor)abletocreateASCIIdatafilesonaharddiscorinaspecializedworkenvironmentsuchasMPLABdescribedlater.

ELEMENTSOFASSEMBLYLANGUAGE

Aprogramwritteninassemblylanguageconsistsofseveralelementsbeingdifferentlyinterpretedwhilecompilingtheprogramintoanexecutabledatafile.Theuseoftheseelementsrequiresstrictrulesanditisnecessarytopayspecialattentiontothemduringprogramwritinginordertoavoiderrors.

ASSEMBLYLANGUAGESYNTAX

Asmentioned,itisnecessarytoobservesomespecificrulesinordertoenabletheprocessofcompilingintoexecutiveHEXcodetorunwithouterrors.Compulsoryrulesexplaininghowsequencesofexpressionsareputtogethertoformthestatementsthatmakeupanassemblylanguageprogramarecalledsyntax.Thereareonlyseveralofthem:

Everyprogramlinemayconsistofamaximumof255charactersEveryprogramlinethatistobecompiledmuststartwithasymbol,label,mnemonicsordirectiveTextfollowingthemark""inaprogramlinerepresentsacommentwhichisignoredbytheassembler(notcompiled)andAlltheelementsofoneprogramline(labels,instructionsetc.)mustbeseparatedbyatleastonespacecharacter.Forthesakeofbetterclearness,apushbuttonTABiscommonlyusedinsteadofit,sothatitiseasytodelimitcolumnswithlabels,directivesetc.inaprogram.

LABELS

AlabelrepresentsatextualversionofsomeaddressinROMorRAMmemory.Eachlabelhastostartinthefirstcolumnwithaletterofalphabetor"_"andmayconsistofmaximumof32characters.Besides,itiseasilyused:

Itissufficienttoenterthenameofalabelinsteadofa16bitaddressininstructionwhichcallssomesubroutineorajump.Thelabelwiththesamenameshouldalsobewrittenatthebeginningofaprogramlineinwhichasubroutinestartsorwhereajumpshouldbeexecuted.Asageneralrule,labelshaveeasilyrecognizablenames.

Duringprogramcompiling,theassemblerwillautomaticallyreplacethelabelsbythecorrespondingaddresses.

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COMMENTS

Acommentisoftenanexplanatorytextwrittenbytheprogrammerinordertomakeaprogramclearerandeasiertounderstand.Itisnotnecessarytocommenteveryline.Whenthreeorfourlinesofcodeworktogethertoaccomplishsomehigherleveltask,itisbettertohaveasinglehigherlevelcommentforthegroupoflines.Therefore,itisaddedifneededandhastostartwith"".Commentsaddedtoassemblysourcecodearenotcompiledintomachinecode.

INSTRUCTIONS

Instructionsaredefinedforeachmicrocontrollerfamilybythemanufacturer.Therefore,itisuptotheusertofollowtherulesoftheirusage.Thewayofwritinginstructionsisalsocalledinstructionsyntax.Theinstructions"movlp"and"gotto",inthefollowingexample,arerecognizedbythePIC16F887microcontrollerasanerrorsincetheyarenotcorrectlywritten.

OPERANDS

Anoperandisavalue(anargument)uponwhichtheinstruction,namedbymnemonic,operates.Theoperandsmaybearegister,avariable,aliteralconstant,alabeloramemoryaddress.

DIRECTIVES

Unlikeinstructionsbeingwrittentoonchipprogrammemoryaftercompilation,directivesarecommandsofassemblylanguageitselfanddonotdirectlyaffecttheoperationofthemicrocontroller.Someofthemmustbeusedineveryprogramwhileothersareonlyusedtofacilitateorenhancetheoperation.Directivesarewrittentothecolumnreservedforinstructions.Therulewhichmustbeobservedallowsonlyonedirectiveperprogramline.

Thissectioncoversonlyafewofthemostcommonlyuseddirectives.Itwouldcertainlytakeuptoomuchspaceandtimetodescribeallthe



directivesrecognizedbytheMPLABprogram.Anyway,acompletelistcontainingalldirectiveswhichtheMPLABassemblercanunderstandisprovidedinHelp.

PROCESSORDirective

Thisdirectivemustbewrittenatthebeginningofeachprogram.Itdefinesthetypeofthemicrocontrollerwhichtheprogramiswrittenfor.Forexample:

Processor16f887

EQUdirective

Thisdirectiveisusedtoreplaceanumericvaluebyasymbol.Inthisway,someaspecificlocationinmemoryisassignedaname.Forexample:

MAXIMUMEQUH25

Thismeansthatamemorylocationataddress25(hex.)isassignedthename"MAXIMUM".Everyappearanceofthelabel"MAXIMUM"intheprogramwillbeinterpretedbytheassemblerastheaddress25(MAXIMUM=H25).Symbolsmaybedefinedthiswayonlyonceinaprogram.Thatthisdirectiveismostlyusedatthebeginningoftheprogram.

ORGdirective

Thisdirectivespecifiesalocationinprogrammemorywheretheprogramfollowingdirectiveistobeplaced.Forexample:

ORG0x100

START......

...

ORG0x1000

TABLE...

...

Thisprogramstartsatlocation0x100.Thetablecontainingdataistobestoredatlocation1024(1000h).

ENDdirective

Eachprogrammustbeendedbyusingthisdirective.Onceaprogramencountersthisdirective,theassemblerimmediatelystopscompiling.Forexample:

...

ENDEndofprogram

\$INCLUDEdirective

Thenameofthisdirectivefullyindicatesitspurpose.Duringcompiling,itenablestheassemblertousedatacontainedinanotherfileonacomputerharddisc.Forexample:

...

#include

CBLOCKandENDCdirectives

Allvariables(theirnamesandaddresses)thatwillbeusedinaprogrammustbedefinedatthebeginningoftheprogram.Becauseofthisitisnotnecessarytospecifytheaddressofeachspecifiedvariablelaterintheprogram.Instead,itisenoughtospecifytheaddressofthefirstonebyusingdirectiveCBLOCKandlistallothersafterwards.Thecompilerautomaticallyassignsthesevariablesthecorrespondingaddressesaspertheordertheyarelisted.Lastly,thedirectiveENDCindicatestheendofthelistofvariables.

CBLOCK0x20

STARTaddress0x20

RELEaddress0x21

STOPaddress0x22

LEFTaddress0x23

RIGHTaddress0x24

ENDC

...

IF,ENDIFandELSEdirectives



Thesedirectivesareusedtocreatesocalledconditionalblocksinaprogram.EachoftheseblocksstartswiththedirectiveIFandendswiththedirectiveENDIForELSE.Astatementorasymbol(inparentheses)followingthedirectiveIFrepresentsaconditionwhichdetermineswhichpartoftheprogramistobecompiled:

Ifthestatementiscorrectorthevalueofasymbolisequaltoone,programcompilesallinstructionswrittenbeforedirectiveELSEorENDIFandIfthestatementisnotcorrectorthevalueofasymbolisequaltozero,onlyinstructionswrittenafterdirectivesELSEorENDIFaretobecompiled.

Example1:

IF(VERSION>3)

CALLTable_2

CALL

ENDIF

...

Iftheprogramisreleasedaftertheversion3(statementisright)thensubroutines"Table2"and"Extension"areexecuted.Ifthestatementinparenthesesiswrong(VERSION



Apartfromtheregularrulesofassemblylanguage,therearealsosomeunwrittenruleswhichshouldbeobservedduringprogramwriting.Oneofthemistowriteinafewwordsatthebeginningofaprogramwhattheprogramsnameis,whatitisusedfor,version,releasedate,typeofthemicrocontrolleritiswrittenforandthenameoftheprogrammer.Sincethisinformationisnotofimportancefortheassembler,itiswrittenasacommentwhichalwaysstartswithsemicolonandcanbewritteninanewlineorimmediatelyafteracommand.

Afterwritingthisgeneralcomment,itistimetoselectthemicrocontrollerbyusingdirectivePROCESSOR.ThisdirectiveisfollowedbyanotheroneusedtoincludeallthedefinitionsofthePIC16F887microcontrollersinternalregistersintheprogram.ThesedefinitionsarenothingbuttheabilitytoaddressportBandotherregistersasPORTBinsteadof06h,whichmakestheprogramclearerandmorelegible.

Inorderthatthemicrocontrollerwilloperateproperly,aseveralparameterssuchasthetypeofoscillator,stateofthewatchdogandinternalresetcircuitmustbedefined.Itisdonebyutilizingthefollowingdirective:

_CONFIG_CP_OFF&_WDT_OFF&PWRTE_ON&XT_OSC

Whenallnecessaryelementsaredefined,theprocessofprogramwritingcanstart.Firstandforemost,itisnecessarytospecifytheaddressfromwhichthemicrocontrollerstartswhenthepowergoeson(org0x00)aswellastheaddressfromwhichtheprogramproceedswithexecutionifaninterruptoccurs(org0x04).Sincethisprogramisverysimple,itisenoughtousecommand"gotoMain"inordertodirectthemicrocontrollertothebeginningoftheprogram.Thenextcommandselectsmemorybank1inordertoenableaccesstotheTRISBregistertoconfigureportBasoutput(bankselTRISB).Themainprogramendsbyselectingmemorybank0andsettingallportBpinstologicone(1)(movlw0xFF,movwfPORTB).

Itisnecessarytocreatealooptokeepprogramfrom"gettinglost"incaseanerroroccurs.Forthispurpose,thereisanendlessloopexecutedallthetimewhilethemicrocontrollerisswitchedon.

"end"isrequiredattheendofeveryprogramtoinformtheassemblerthattherearenomorecommandstobecompiled.

DATAFILESRESULTINGFROMPROGRAMCOMPILING

Theresultofcompilingaprogramwritteninassemblylanguagearedatafiles.Themostimportantandmostcommonlyuseddatafilesare:

Executivedatafile(Program_Name.HEX)Errordatafile(Program_Name.ERR)andListdatafile(Program_Name.LST).

Thefirstfilecontainscompiledprogramwhichisloadedintothemicrocontroller.Itscontentsgivenoinformationofimportancetotheprogrammersoitwillnotbediscussedhere.Thesecondfilecontainserrorsmadeinwritingprocessanddetectedbythecompilerduringcompilingprocess.Errorscanbedetectedinlistdatafile,whichtakesmoretime,sotheerrordatafileismoresuitableforlongprograms.

Thethirdfileisthemostusefulfortheprogrammer.Itcontainslotsofinformationoncommandsandvariableslocationsinonchipmemoryaswellaserrorsignalization.Thereisasymboltableattheendofeachdatafilelistcontainingallthesymbolsusedinaprogram.Otherusefulelementsoflistdatafilearememoryusagemapsanderrorstatisticsprovidedattheveryendofthefilelist.

MACROSANDSUBROUTINES

Thesamesequenceofcomputinginstructionsisusuallyusedrepeatedlywithinaprogram.Assemblylanguageisverydemanding.The



programmerisrequiredtotakecareofthelastlittledetailwhenwritingaprogram,becauseonlyonewrongcommandorlabelnamemaycausetheprogramtonotworkproperlyoritmaynotworkatall.Therefore,itislesstediousandlesserrorpronetouseasequenceofinstructionsasasingleprogramstatementwhichworksproperlyforsure.Toimplementthisidea,macrosandsubroutinesareused.

MACROS

Amacrocontainsprogrammerdefinedsymbolsthatstandforasequenceoftextlines.Itisdefinedbyusingdirectivemacrowhichnamesmacroandargumentsifneeded.Macromustbedefinedprioritisused.Onceamacrohasbeendefined,itsnamemaybeusedintheprogram.Whentheassemblerencountersmacrosname,itreplacesitbytheappropriatesequenceofinstructionsandprocessesthemjustasthoughtheyhaveappearedintheprogram.Manydifferentmacroinstructionsareavailableforvariouspurposes,eliminatingsomeoftherepetitivenessoftheprogramming,aswellassimplifyingthewriting,readingandunderstandingoftheprogram.Thesimplestuseofmacrosmaybegivinganametoaninstructionsequencebeingrepeated.Letustake,forexample,globalinterruptenableprocedure,SFRs'bankselection.

macro_namemacroarg1,arg2...

...

sequenceofinstructions

...

endm

Thefollowingexampleshowsfourmacros.Thefirsttwomacrosselectbanks,thethirdoneenablesinterrupt,whereasthefourthonedisablesinterrupt.

bank0macroMacrobank0

bcfSTATUS,RP0ResetRP0bit


endmEndofmacro

bank1macroMacrobank1

bsfSTATUS,RP0SetRP0bit


endmEndofmacro

enableintmacroGlobalinterruptenable

bsfINTCON,7Setbit

endmEndofmacro

disableintmacroGlobalinterruptdisable

bcfINTCON,7ResetbitendmEndofmacro

MacrosdefinedinthiswayaresavedinaparticulardatafilewithextensionINCwhichstandsforINCLUDEdatafile.Asseen,thesefourmacrosdonothavearguments.However,macrosmayincludeargumentsifneeded.

Thefollowingexampleshowsmacroswitharguments.PinisconfiguredasinputifthecorrespondingbitoftheTRISregisterissettologicone(bank1).Otherwise,itisconfiguredasoutput.

inputmacroarg1,arg2MacroInput

bank1BankcontainingTRISregisters

bsfarg1,arg2Setthespecifiedbit(1=Input)

bank0Macroforbank0selection

endmEndofmacro

outputmacroarg1,arg2MacroOutput

bank1BankcontainingTRISregisters

bcfarg1,arg2Clearthespecifiedbit(0=Output)

bank0Macroforbank0selection

endmEndofmacro

Macrowithargumentsmaybecalledinthefollowingway:

...

outputTRISB,7PinRB7isconfiguredasoutput

...

Whencallingthismacro,thefirstspecifiedargumentTRISBisreplacedbythefirstargumentarg1inmacrodefinition.Similarly,number7isreplacedbytheargumentarg2,andthefollowingcodeisgenerated:

...

bsfSTATUS,RP0SetRP0bit=BANK1



bcfSTATUS,RP1ResetRP0bit=BANK1

bcfTRISB,7ConfigureRB7asoutput

bcfSTATUS,RP0ClearRP0bit=BANK0

bcfSTATUS,RP1ClearRP1bit=BANK0

...

Itisclearatfirstsightthattheprogrambecomesmorelegibleandflexiblebyusingmacros.Themaindisadvantageofmacroisthatitoccupiesalotofmemoryspacebecauseeverymacronameinaprogramisreplacedbyitspredefinedcode.Owingtothefactthatprogramsoftenusemacro,everythingismorecomplicatedifitislong.

callcmacrolabelMacrocallc

localExitDefinelocalLabelwithinmacro

bncExitIfC=0jumptoExit

calllabelIfC=1callsubroutineataddressLabel(outofmacro)

ExitLocalLabelwithinmacro

endmEndofmacro

Intheeventthatamacrohaslabels,theymustbedefinedaslocalonesbyusingdirectivelocal.Thegivenexamplecontainsmacrowhichcallsasubroutine(calllabelinthiscase)iftheCarrybitoftheSTATUSregisterisset.Otherwise,thefirstfollowinginstructionisexecuted.

SUBROUTINES

Asubroutinecontainsasequenceofinstructions,beginswithalabel(subroutine_name)andendswithcommandreturnorretlw.Themaindifferencecomparingtomacroisthatsubroutineisnotreplacedbyitscodeintheprogram,butprogramjumpstosubroutinetoexecuteit.IthappenseverytimetheassemblerencounterscommandcallSubroutine_nameintheprogram.Onthecommandreturn,itleavesasubroutineandcontinuesexecutionfromwhereitleftoffthemainprogram.Subroutinemaybedefinedbothpriortooruponthecall.

Asseen,concerningmacros,theinputandoutputargumentsareofgreatimportance.Concerningsubroutines,itisnotpossibletodefineargumentswithinthesubroutineitself.However,variablespredefinedinthemainprogrammaybeusedassubroutinearguments.

Alogicalsequenceofeventsisasfollows:definingvariables,callingsubroutinewhichusesthemandattheendreadingvariableschangedupontheexecutionofsubroutine.

Theprograminthefollowingexampleperformsadditionoftwo2bytevariablesARG1andARG2andmovesresulttothevariableRES.When2bytevariablesareused,itisnecessarytodefinehigherandlowerbyteforeachofthem.Theprogramitselfisverysimple.ItfirstaddslowerbytesofvariablesARG1andARG2andhigherafterwards.Ifthesumofadditionoftwolowerbytesisgreaterthan255(maximalbytevalue)theremainderisaddedtotheRESHvariable.

Programtoaddtwo16bitnumbers

Version:1.0Date:April25,2007MCU:PIC16F887

PROCESSOR16f887Definingprocessor

#include"p16f887.inc"MicrochipINCdatabase

__CONFIG_CP_OFF&_WDT_OFF&_PWRTE_ON&_XT_OSC

Cblock0x20BeginningofRAM

ARG1HArgument1higherbyte

ARG1LArgument1lowerbyte

ARG2HArgument2higherbyte

ARG2LArgument2lowerbyte

RESHResulthigherbyte

RESLResultlowerbyte

endcEndofvariables

ORG0x00Resetvector

gotoStart

StartWritevaluestovariables



movlw0x01ARG1=0x0104

movwfARG1H

movlw0x04

movwfARG1L

movlw0x07ARG2=0x0705

movwfARG2H

movlw0x05

movwfARG2L

MainMainprogram

callAdd16CallsubroutineAdd16

LoopgotoLoopRemainhere

Add16Subroutinetoaddtwo16bitnumbers

clrfRESHRESH=0

movfARG1L,ww=ARG1L

addwfARG2L,ww=w+ARG2L

movwfRESLRESL=w

btfscSTATUS,CIstheresultgreaterthan255?

incfRESH,fIfgreater,incrementRESHbyone

movfARG1H,ww=ARG1H

addwfARG2H,ww=w+ARG2

addwfRESH,fRESH=w

returnReturnfromsubroutine

endEndofprogram

InShort

Themaindifferencebetweenmacrosandsubroutinesisthatmacroisaftercompilingreplacedbyitscode(enablestheprogrammertotypeless).Itmayalsohaveargumentswhilesubroutineuseslessmemory,butdoesnothavearguments.

MPLAB

MPLABisaWindowsprogrampackagewhichenableseasyprogramwritingaswellaseasyprogramdevelopment.ItisbesttodescribeitasdevelopmentenvironmentforastandardprogramlanguagedesignedforPCprogramming.MPLABtechnicallysimplifiessomeoperationsconsistingofalotofparameters,which,untiltheIDEenvironment*appeared,wereexecutedfromthecommandline.However,tastesaredifferentandtherearesomeprogrammerswhopreferstandardeditorsandcommandlinecompilers.EveryprogramwritteninMPLABisclear,buttherearealsohelpdocumentationjustincase.

INSTALLINGMPLAB

MPLABconsistsofseveralparts:

Theprogramwhichsortsdatafilesofthesameprojectintoonegroup(ProjectManager)programfortextgeneratingandprocessing(TextEditor)andsimulatorusedtosimulatetheoperationofaprogramloadedintothemicrocontroller.

Besides,therearealsobuiltinprogrammerssuchasPICStartPlusandICD(InCircuitDebugger)thatcanbeusedtoprogramsoftwareintoPICmicrocontrollerdevice.Sincenotbeingthesubjectofthisbook,theyarementionedasoptionsonly.

InordertostartMPLAB,yourPCshouldcontain:

PCcompatiblecomputerbelongingtoclass486orbetterAnyWindowsoperatingsystemVGAgraphiccard8MBmemory(32MBrecommended)200MBavailableharddiscandAmouse.

MPLABinstallationcomesfirst.DatafilesfromMPLABCDshouldbecopiedtoaharddisc.TheprocessofinstallationissimilartoalmostallotherWindowsprograminstallations.Firstofallawelcomewindowappears,thenoptionstoselectandatlastinstallationitself.Amessagenotifyingthattheprogramissuccessfullyinstalledandreadyforuseappears.Areyouready?

Stepstofollowpriortheinstallation:

Everythingisreadynowtostartinstallation.Thefollowingpicturesdescribetheinstallationsteps.

1. StartMicrosoftWindows2. InserttheCDintoCDROM3. ClickSTARTandselectoptionRUN4. ClickBROWSEandselectCDROMdriveand5. FindfolderMPLABonCDROM.



Nextwindowcontainstheword"Welcome".Needexplanation?

Actually,theprogramremindsyoutocloseallactiveprogramsinordertonotinterferewiththeinstallationprocess.Nextofcourse!

Priortocontinue,youhavetoaccepttheMPLABsoftwarelicenseconditions.Selecttheoption"Iaccept"andclickNEXT.

Doyouwanttoinstalltheentiresoftware?Yes.Next...

Similartootherprograms,MPLABshouldbealsoinstalledintoafolder.Itmaybeanyfolderonanyharddisc.Ifitisnotnecessarytomakechanges,selectthespecifiedaddressandclickNext.

Clickonthisicontostartuptheprocess...

Somethingisgoingon...Thepicturecomingupindicatesthattheprocessofinstallationhasjuststarted!



Anotherlicense,anotheracceptanceofoptionsspecifiedbythecomputer...Next,Next...

Bepatient!

Finally!Thisiswhatyouhavebeenwaitingfor.ClickFinish.Thecomputerwillberestartedalongwiththeprogramsavedonharddisc.EverythingisOK!

ClicktheMPLABdesktopiconinordertostarttheprogramandlearnaboutit.



KeeponprojectmakingbyclickingNEXT.Thenselectthemicrocontrolleryouwillbeusing.

Asseen,MPLABissimilartomostWindowsprograms.Apartfromtheworkingarea,therearemenus(containsoptions:File,Editetc.),toolbars(containsdifferenticons)andastatusbaratthebottomofthewindow.SimilartoWindows,thereisaruletohaveshortcutsforthemostcommonlyusedprogramoptionscreatedinordertoeasilyaccessthemandspeedupoperationtherefore.Theseshortcutsareactuallyiconsbelowthemenubar.Inotherwords,alloptionscontainedinthetoolbararecontainedinthemenutoo.

PROJECTMAKING

Followthesestepstoprepareprogramforloadingintothemicrocontroller:

Inordertomakeaproject,itisnecessarytoclicktheoption"PROJECT"andthen"PROJECTWIZARD".Awelcomewindowappears.

1. Makeaproject2. Writeaprogramand3. Compileit.



Inourcase,itisPIC16F887microcontroller.

Attheend,theprojectisassignedanamewhichusuallyindicatesthepurposeandthecontentoftheprogrambeingwritten.Theprojectshouldbemovedtothedesiredfolder.ItisbestthatthefolderassociateswithPICmicrocontrollers(Seefigure).

DocumentscontainedintheprojectdonotalwaysneedtobewritteninMPLAB.Documentswrittenbysomeotherprogrammayalsobeincludedintheproject.Inthisexample,therearenosuchdocuments.JustclickNext.

ClickFINISHtocompletetheproject.Thewindowitselfcontainsprojectparameters.

WRITINGANEWPROGRAM

Whentheprojectiscreated,awindowshowninfigurebelowappears.



Afterthe"Blink.asm"iscreatedandsaved,itshouldbeincludedintheprojectbyrightclickonthe"SourceFiles"optioninthe"Proba.mcw"window.Afterthat,asmallwindowwithtwooptionsappears.Selectthefirstone"AddFiles".

Thenextstepistowriteaprogram.OpenanewdocumentbyclickingFile>New.TextEditorinMPLABenvironmentappears.

SavethedocumentinthefolderD:\PICprojectsbyusingtheFile>SaveAscommandandnameit"Blink.asm"indicatingthatthisprogramistobeanexampleofportdiodeblinking.Obviouslyyoucanlocateyoufileswhereveryouwish,inwhicheverharddriveyouwish.Usingacommondirectorytostoreallyourdifferentprojectsandsubdirectoriesinmakesgoodsense.

Example:

D:\PicProjects

LEDFlashProject

Allassociatedfiles

EventCountProject

Allassociatedfiles

LEDScanningProject

Allassociatedfiles

ClickonthatoptionopensanotherwindowcontainingthefolderPICalongwiththedocumentBlink.asm.Seefigurebelow.



Click"Blink"toincludethedocumentBlink.asmintotheproject.

Programwritingexample

Theprogramwritingprocedurecannotstartuntilallpreviousoperationshavebeenperformed.Programwrittenbelowisasimpleillustrationofprojectmaking.

ProgramtosetportBpinstologicone(1).

Version:1.0Date:April25,2007MCU:PIC16F887Programmer:JohnSmith

*****Declarationandconfigurationofthemicrocontroller*****

PROCESSOR16f887

#include"p16f887.inc"

__CONFIG_CP_OFF&_WDT_OFF&_PWRTE_ON&_XT_OSC

*****Variabledeclaration*****

Cblock0x20FirstfreeRAMlocation

endcNovariables

*****Programmemorystructure*****

ORG0x00Resetvector

gotoMainAfterresetjumptothislocation

ORG0x04Interruptvector

gotoMainNointerruptroutine

MainStarttheprogram

bankselTRISBSelectbankcontainingTRISB

clrfTRISBPortBisconfiguredasoutput

bankselPORTBSelectbankcontainingPORTB

movlw0xffW=FF

movwfPORTBMoveWtoportB

LoopgotoLoopJumptolabelLoop

End

TheprogramshouldbewrittentotheBlink.asmwindoworcopiedfromdiscbymeansofoptionscopy/paste.Whencopied,theprogramshouldbecompiledintoexecutableHEXformatbyusingoptionPROJECT>BUILDALL.Anewwindowappears.Thelastsentenceisthemostimportantbecauseittellsuswhethercompilinghassucceededornot.Clearly,BUILDSUCCEEDEDmessagemeansthatnoerroroccurredandcompilinghasbeensuccessfullydone.

Incaseanerroroccurs,itisnecessarytoclicktwiceonthemessagereferringtoitintheOutputwindow,whichautomaticallyswitchyouovertoassemblyprogram,directlytothelinewheretheerrorhasoccurred.



Startsprogramexecutionatfullspeed.Inthisexample,thesimulatorexecutestheprogramatfull(normal)speeduntilitishaltedbyclickingtheiconbelow.

Pausesprogramexecution.Programcancontinueexecutingstepbysteporatfullspeedagain.

Startsprogramexecutionatoptionalspeed.ThespeedofexecutionissetindialogDebugger/Settings/Animation/RealtimeUpdates.

Startsstepbystepprogramexecution.Instructionsareexecutedoneafteranother.Furthermore,clickingonthisiconenablesyoutostepintosubroutinesandmacros.

Thisiconhasthesamefunctionasthepreviousoneexceptithastheabilitytostepintosubroutines.

Resetsmicrocontroller.Byclickingthisicon,theprogramcounterispositionedatthebeginningoftheprogramandsimulationcanstart.

SIMULATOR

AsimulatorisapartofMPLABenvironmentwhichprovidesbetterinsightintotheoperationofthemicrocontroller.Generallyspeaking,asimulationisanattempttomodelareallifeorhypotheticalsituationsothatitcanbestudiedtoseehowthesystemworks.Bymeansofthesimulator,itisalsopossibletomonitorcurrentvaluesofvariables,registersandportpinsstatesaswell.Tobehonest,asimulatorisnotofthesameimportanceforallprograms.Ifaprogramissimpler(asinourexample),thesimulationisnotofgreatimportancebecausesettingportBpinstologicone(1)isnotcomplicatedatall.However,inmorecomplexprogramscontainingtimers,differentconditionsandrequests(especiallymathematicaloperations),thesimulatormaybeofgreatuse.Asthenameitselfindicates,asimulationmeanstosimulatetheoperationofmicrocontroller.Likethemicrocontroller,asimulatorexecutesinstructionsoneafteranother(linebyline)andconstantlyupdatesthestateofallregisters.Inthisway,theusersimplymonitorsprogramexecution.Attheendofprogramwriting,theusershouldfirsttestitinthesimulatorpriortoexecutingitinarealenvironment.Unfortunately,thisisoneofmanygoodthingsbeingoverlookedbytheprogrammerbecauseofitscharacterassuchandthelackofhighqualitysimulatorsaswell.

SimulatorisactivatedbyclickingonDEBUGGER>SELECTTOOL>MPLABSIM,asshowninfigure.Asaresult,severaliconsrelatedtothesimulatoronlyappear.Theirmeaningsareasfollows:



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Similartorealenvironment,thefirstthingthatshouldbedoneistoresetthemicrocontrollerusingtheoptionDEBUGGER>RESETorbyclickingreseticon.Astheconsequenceofthis,agreenlineispositionedatthebeginningoftheprogramandprogramcounterPCLisclearedtozero.RefertothewindowSpecialFunctionRegistersshownbelow.

ApartfromSFRs,itisgoodtohaveaninsightinFileRegisters.AwindowcontainingthemappearsbyclickingtheVIEW>FILEREGISTERSoption.

Iftheprogramcontainsvariables,itisgoodtomonitortheirvaluesaswell.Eachvariableisassignedawindow(WatchWindows)byclickingVIEW>WATCHoption.

Iftheprogramcontainsvariables,itisgoodtomonitortheirvaluesaswell.Eachvariableisassignedawindow(WatchWindows)byclickingVIEW>WATCHoption.

Afterallvariablesandregistersofinterestbecomeavailableonthesimulatorworkingarea,theprocessofsimulationcanstart.ThenextinstructionmaybeeitherStepintoorStepoverdependingonwhetheryouwanttostepintosubroutineornot.Thesameinstructionsmaybesetbyusingkeyboardpushbuttonsor(generally,allimportantinstructionshavethecorrespondingpushbuttonsonthekeyboard).

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Appendix A_ Programming a Microcontroller - Book_ PIC Microcontrollers

Documents

pic microcontrollershttp

microcontroller book

toc introduction