HT66F25D datasheet(19/177 Pages) HOLTEK

19 / 177 page

A/D Flash Type 8-bit MCU with EEPROM

HT66F24D/HT66F25D

Rev. 1.00

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Rev. 1.00

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Fe tc h In st . 2

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

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

Forinstructionsinvolvingbranches,suchasjumporcallinstructions,twomachinecyclesare

requiredtocompleteinstructionexecution.Anextracycleisrequiredastheprogramtakesone

cycletofirstobtaintheactualjumporcalladdressandthenanothercycletoactuallyexecutethe

branch.Therequirementforthisextracycleshouldbetakenintoaccountbyprogrammersintiming

sensitiveapplications.

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.

Device

Program Counter

High Byte

Low Byte (PCL Register)

HT��F�4D

PC10~PC8

PCL7~PCL0

HT��F�5D

PC11~PC8

PCL7~PCL0

Program Counter

ThelowerbyteoftheProgramCounter,knownastheProgramCounterLowregisterorPCL,is

availableforprogramcontrolandisareadableandwriteableregister.Bytransferringdatadirectly

intothisregister,ashortprogramjumpcanbeexecuteddirectly,however,asonlythislowbyteis

availableformanipulation,thejumpsarelimitedtothepresentpageofmemory,thatis256locations.

Whensuchprogramjumpsareexecuteditshouldalsobenotedthatadummycyclewillbeinserted.

ManipulatingthePCLregistermaycauseprogrambranching,soanextracycleisneededtopre-fetch.

HT66F25D Datasheet(PDF) 19 Page - Holtek Semiconductor Inc

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