ETIC 2230 Guia do Utilizador descarregar pdf (Página 17)

Rev. 1.10 16 November 14, 2014 Rev. 1.10 17 November 14, 2014

HT66FW2230

Wireless Charger A/D Flash 8-Bit MCU

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      

   

Instruction Fetching

Program Counter

Duringprogramexecution,theProgramCounterisusedtokeeptrackoftheaddressofthe

nextinstructiontobeexecuted.Itisautomaticallyincrementedbyoneeachtimeaninstruction

isexecutedexceptforinstructions,suchas“JMP”or“CALL”thatdemandajumptoanon-

consecutiveProgramMemoryaddress.Onlythelower8bits,knownastheProgramCounterLow

Whenexecutinginstructionsrequiringjumpstonon-consecutiveaddressessuchasajump

instruction,asubroutinecall,interruptorreset,etc.,themicrocontrollermanagesprogramcontrol

byloadingtherequiredaddressintotheProgramCounter.Forconditionalskipinstructions,once

theconditionhasbeenmet,thenextinstruction,whichhasalreadybeenfetchedduringthepresent

instructionexecution,isdiscardedandadummycycletakesitsplacewhilethecorrectinstructionis

obtained.

Program Counter

Program Counter High byte PCL Register

PC11~PC8 PCL7~PCL0

ThelowerbyteoftheProgramCounter,knownastheProgramCounterLowregisterorPCL,is

availableforprogramcontrolandisareadableandwriteableregister.Bytransferringdatadirectly

intothisregister,ashortprogramjumpcanbeexecuteddirectly,however,asonlythislowbyte

isavailableformanipulation,thejumpsarelimitedtothepresentpageofmemory,thatis256

locations.Whensuchprogramjumpsareexecuteditshouldalsobenotedthatadummycycle

willbeinserted.ManipulatingthePCLregistermaycauseprogrambranching,soanextracycleis

neededtopre-fetch.

Stack

ThisisaspecialpartofthememorywhichisusedtosavethecontentsoftheProgramCounter

only.Thestackisneitherpartofthedatanorpartoftheprogramspace,andisneitherreadablenor

writeable.TheactivatedlevelisindexedbytheStackPointer,andisneitherreadablenorwriteable.

Atasubroutinecallorinterruptacknowledgesignal,thecontentsoftheProgramCounterarepushed

ontothestack.Attheendofasubroutineoraninterruptroutine,signaledbyareturninstruction,

RETorRETI,theProgramCounterisrestoredtoitspreviousvaluefromthestack.Afteradevice

reset,theStackPointerwillpointtothetopofthestack.

Ifthestackisfullandanenabledinterrupttakesplace,theinterruptrequestagwillberecorded

buttheacknowledgesignalwillbeinhibited.WhentheStackPointerisdecremented,byRETor

RETI,theinterruptwillbeserviced.Thisfeaturepreventsstackoverowallowingtheprogrammer

tousethestructuremoreeasily.However,whenthestackisfull,aCALLsubroutineinstructioncan

stillbeexecutedwhichwillresultinastackoverow.Precautionsshouldbetakentoavoidsuch

caseswhichmightcauseunpredictableprogrambranching.Ifthestackisoverow,therstProgram

Countersaveinthestackwillbelost.

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