HT45F5Q datasheet(17/114 Pages) HOLTEK

17 / 114 page

Rev. 1.10

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HT45F5Q

Charger Flash MCU

HT45F5Q

Charger Flash MCU

Fe tc h In st . 1E xe cu te I ns t. 1

Fe tc h In st . 2

Fl us h Pi pel in e

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

Fe tc h In st . 3

Fe tc h In st . 6

Ex ec ut e In s t. 6

Fe tc h In st . 7

Instruction Fetching

Program Counter

Duringprogramexecution,theProgramCounterisusedtokeeptrackoftheaddressofthe

nextinstructiontobeexecuted.Itisautomaticallyincrementedbyoneeachtimeaninstruction

isexecutedexceptforinstructions,suchas“JMP”or“CALL”thatdemandajumptoanon-

consecutiveProgramMemoryaddress.Onlythelower8bits,knownastheProgramCounterLow

Whenexecutinginstructionsrequiringjumpstonon-consecutiveaddressessuchasajump

instruction,asubroutinecall,interruptorreset,etc.,themicrocontrollermanagesprogramcontrol

byloadingtherequiredaddressintotheProgramCounter.Forconditionalskipinstructions,once

theconditionhasbeenmet,thenextinstruction,whichhasalreadybeenfetchedduringthepresent

instructionexecution,isdiscardedandadummycycletakesitsplacewhilethecorrectinstructionis

obtained.

Program Counter

Program Counter High byte

PCL Register

PC10~PC8

PCL7~PCL0

ThelowerbyteoftheProgramCounter,knownastheProgramCounterLowregisterorPCL,is

availableforprogramcontrolandisareadableandwriteableregister.Bytransferringdatadirectly

intothisregister,ashortprogramjumpcanbeexecuteddirectly,however,asonlythislowbyte

isavailableformanipulation,thejumpsarelimitedtothepresentpageofmemory,thatis256

locations.Whensuchprogramjumpsareexecuteditshouldalsobenotedthatadummycycle

willbeinserted.ManipulatingthePCLregistermaycauseprogrambranching,soanextracycleis

neededtopre-fetch.

Stack

ThisisaspecialpartofthememorywhichisusedtosavethecontentsoftheProgramCounter

only.Thestackisneitherpartofthedatanorpartoftheprogramspace,andisneitherreadablenor

writeable.TheactivatedlevelisindexedbytheStackPointer,andisneitherreadablenorwriteable.

Atasubroutinecallorinterruptacknowledgesignal,thecontentsoftheProgramCounterarepushed

ontothestack.Attheendofasubroutineoraninterruptroutine,signaledbyareturninstruction,

RETorRETI,theProgramCounterisrestoredtoitspreviousvaluefromthestack.Afteradevice

reset,theStackPointerwillpointtothetopofthestack.

Ifthestackisfullandanenabledinterrupttakesplace,theinterruptrequestflagwillberecorded

buttheacknowledgesignalwillbeinhibited.WhentheStackPointerisdecremented,byRETor

RETI,theinterruptwillbeserviced.Thisfeaturepreventsstackoverflowallowingtheprogrammer

tousethestructuremoreeasily.However,whenthestackisfull,aCALLsubroutineinstructioncan

stillbeexecutedwhichwillresultinastackoverflow.Precautionsshouldbetakentoavoidsuch

caseswhichmightcauseunpredictableprogrambranching.Ifthestackisoverflow,thefirstProgram

Countersaveinthestackwillbelost.

HT45F5Q Datasheet(PDF) 17 Page - Holtek Semiconductor Inc

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