HT69F240 datasheet(17/172 Pages) HOLTEK

17 / 172 page

Rev. 1.20

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Rev. 1.20

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HT69F240

I/O 8-Bit Flash MCU with LED/LCD Driver

HT69F240

I/O 8-Bit Flash MCU with LED/LCD Driver

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Fl us h Pi pel in e

6 DE LA Y:

MO V A, [1 2H ]

CA LL D EL AY

CP L [ 12H ]

NO P

Ex ec ut e In st . 2

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Ex ec ut e In s t. 6

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Instruction Fetching

Program Counter

Duringprogramexecution,theProgramCounterisusedtokeeptrackoftheaddressofthenext

instructiontobeexecuted.Itisautomaticallyincrementedbyoneeachtimeaninstructionis

executedexceptforinstructions,suchas"JMP"or"CALL"thatdemandajumptoanon-consecutive

ProgramMemoryaddress.Onlythelower8bits,knownastheProgramCounterLowRegister,are

directlyaddressablebytheapplicationprogram.

Whenexecutinginstructionsrequiringjumpstonon-consecutiveaddressessuchasajumpinstruction,

asubroutinecall,interruptorreset,etc.,themicrocontrollermanagesprogramcontrolbyloading

therequiredaddressintotheProgramCounter.Forconditionalskipinstructions,oncethecondition

hasbeenmet,thenextinstruction,whichhasalreadybeenfetchedduringthepresentinstruction

execution,isdiscardedandadummycycletakesitsplacewhilethecorrectinstructionisobtained.

ThelowerbyteoftheProgramCounter,knownastheProgramCounterLowregisterorPCL,is

availableforprogramcontrolandisareadableandwriteableregister.Bytransferringdatadirectly

intothisregister,ashortprogramjumpcanbeexecuteddirectly,however,asonlythislowbyteis

availableformanipulation,thejumpsarelimitedtothepresentpageofmemory,thatis256locations.

Whensuchprogramjumpsareexecuteditshouldalsobenotedthatadummycyclewillbeinserted.

ManipulatingthePCLregistermaycauseprogrambranching,soanextracycleisneededtopre-fetch.

Stack

ThisisaspecialpartofthememorywhichisusedtosavethecontentsoftheProgramCounteronly.

Thestackhasmultiplelevelsdependinguponthedeviceandisneitherpartofthedatanorpartof

theprogramspace,andisneitherreadablenorwriteable.TheactivatedlevelisindexedbytheStack

Pointer,andisneitherreadablenorwriteable.Atasubroutinecallorinterruptacknowledgesignal,the

contentsoftheProgramCounterarepushedontothestack.Attheendofasubroutineoraninterrupt

routine,signaledbyareturninstruction,RETorRETI,theProgramCounterisrestoredtoitsprevious

valuefromthestack.Afteradevicereset,theStackPointerwillpointtothetopofthestack.

Ifthestackisfullandanenabledinterrupttakesplace,theinterruptrequestflagwillberecordedbut

theacknowledgesignalwillbeinhibited.WhentheStackPointerisdecremented,byRETorRETI,

theinterruptwillbeserviced.Thisfeaturepreventsstackoverflowallowingtheprogrammertouse

thestructuremoreeasily.However,whenthestackisfull,aCALLsubroutineinstructioncanstill

beexecutedwhichwillresultinastackoverflow.Precautionsshouldbetakentoavoidsuchcases

whichmightcauseunpredictableprogrambranching.

HT69F240 Datasheet(PDF) 17 Page - Holtek Semiconductor Inc

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