HT45F4M datasheet(15/138 Pages) HOLTEK

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HT45F4M

Lithium Battery Backup Power ASSP MCU

HT45F4M

Lithium Battery Backup Power ASSP MCU

Forinstructionsinvolvingbranches,suchasjumporcallinstructions,twomachinecyclesare

requiredtocompleteinstructionexecution.Anextracycleisrequiredastheprogramtakesone

cycletofirstobtaintheactualjumporcalladdressandthenanothercycletoactuallyexecutethe

branch.Therequirementforthisextracycleshouldbetakenintoaccountbyprogrammersintiming

sensitiveapplications.

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Instruction Fetching

Program Counter

Duringprogramexecution,theProgramCounterisusedtokeeptrackoftheaddressofthe

nextinstructiontobeexecuted.Itisautomaticallyincrementedbyoneeachtimeaninstruction

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

consecutiveProgramMemoryaddress.Onlythelower8bits,knownastheProgramCounterLow

Whenexecutinginstructionsrequiringjumpstonon-consecutiveaddressessuchasajumpinstruction,

asubroutinecall,interruptorreset,etc.,themicrocontrollermanagesprogramcontrolbyloadingthe

requiredaddressintotheProgramCounter.Forconditionalskipinstructions,oncetheconditionhas

beenmet,thenextinstruction,whichhasalreadybeenfetchedduringthepresentinstructionexecution,

isdiscardedandadummycycletakesitsplacewhilethecorrectinstructionisobtained.

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.

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