Holtek HT66F0175 - Page 25

Rev. 1.50 24 August 28, 2017 Rev. 1.50 25 August 28, 2017
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
Forinstructionsinvolvingbranches,suchasjumporcallinstructions,twomachinecyclesare
requiredtocompleteinstructionexecution.Anextracycleisrequiredastheprogramtakesone
cycletorstobtaintheactualjumporcalladdressandthenanothercycletoactuallyexecutethe
branch.Therequirementforthisextracycleshouldbetakenintoaccountbyprogrammersintiming
sensitiveapplications.
     
   
 







  
 
  



 
   
     
   
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
Register,aredirectlyaddressablebytheapplicationprogram.
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.
Device
Program Counter
High Byte Low Byte (PCL)
HT66F0175 PC10~PC8 PC7~PC0
HT66F0185 PC11~PC8 PC7~PC0
Program Counter
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.