HT45F12
8-Bit Flash MCU with Op Amps & Comparators
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Instruction Fetching
Program Counter – PC
Duringꢀprogramꢀexecution,ꢀtheꢀProgramꢀCounterꢀisꢀusedꢀtoꢀkeepꢀtrackꢀofꢀtheꢀaddressꢀofꢀtheꢀ
nextꢀinstructionꢀtoꢀbeꢀexecuted.ꢀItꢀisꢀautomaticallyꢀincrementedꢀbyꢀoneꢀeachꢀtimeꢀanꢀinstructionꢀ
isꢀexecutedꢀexceptꢀforꢀinstructions,ꢀsuchꢀasꢀ“JMP”ꢀorꢀ“CALL”ꢀthatꢀdemandꢀaꢀjumpꢀtoꢀaꢀnon-
consecutiveꢀProgramꢀMemoryꢀaddress.ꢀItꢀmustꢀbeꢀnotedꢀthatꢀonlyꢀtheꢀlowerꢀ8ꢀbits,ꢀknownꢀasꢀtheꢀ
ProgramꢀCounterꢀLowꢀRegister,ꢀareꢀdirectlyꢀaddressableꢀbyꢀuser.
Whenꢀexecutingꢀinstructionsꢀrequiringꢀjumpsꢀtoꢀnon-consecutiveꢀaddressesꢀsuchꢀasꢀaꢀjumpꢀ
instruction,ꢀaꢀsubroutineꢀcall,ꢀinterruptꢀorꢀreset,ꢀetc.ꢀtheꢀmicrocontrollerꢀmanagesꢀprogramꢀcontrolꢀ
byꢀloadingꢀtheꢀrequiredꢀaddressꢀintoꢀtheꢀProgramꢀCounter.ꢀForꢀconditionalꢀskipꢀinstructions,ꢀonceꢀ
theꢀconditionꢀhasꢀbeenꢀmet,ꢀtheꢀnextꢀinstruction,ꢀwhichꢀhasꢀalreadyꢀbeenꢀfetchedꢀduringꢀtheꢀpresentꢀ
instructionꢀexecution,ꢀisꢀdiscardedꢀandꢀaꢀdummyꢀcycleꢀtakesꢀitsꢀplaceꢀwhileꢀtheꢀcorrectꢀinstructionꢀisꢀ
obtained.
Program Counter
Program Counter High Byte
PCL Register
PC9~PC8
PCL7~PCL0
TheꢀlowerꢀbyteꢀofꢀtheꢀProgramꢀCounter,ꢀknownꢀasꢀtheꢀProgramꢀCounterꢀLowꢀregisterꢀorꢀPCL,ꢀisꢀ
availableꢀforꢀprogramꢀcontrolꢀandꢀisꢀaꢀreadableꢀandꢀwriteableꢀregister.ꢀByꢀtransferringꢀdataꢀdirectlyꢀ
intoꢀthisꢀregister,ꢀaꢀshortꢀprogramꢀjumpꢀcanꢀbeꢀexecutedꢀdirectly,ꢀhowever,ꢀasꢀonlyꢀthisꢀlowꢀbyteꢀ
isꢀavailableꢀforꢀmanipulation,ꢀtheꢀjumpsꢀareꢀlimitedꢀtoꢀtheꢀpresentꢀpageꢀofꢀmemory,ꢀthatꢀisꢀ256ꢀ
locations.ꢀWhenꢀsuchꢀprogramꢀjumpsꢀareꢀexecutedꢀitꢀshouldꢀalsoꢀbeꢀnotedꢀthatꢀaꢀdummyꢀcycleꢀwillꢀ
beꢀinserted.ꢀ
TheꢀlowerꢀbyteꢀofꢀtheꢀProgramꢀCounterꢀisꢀfullyꢀaccessibleꢀunderꢀprogramꢀcontrol.ꢀManipulatingꢀtheꢀ
PCLꢀmightꢀcauseꢀprogramꢀbranching,ꢀsoꢀanꢀextraꢀcycleꢀisꢀneededꢀtoꢀpre-fetch.ꢀFurtherꢀinformationꢀ
onꢀtheꢀPCLꢀregisterꢀcanꢀbeꢀfoundꢀinꢀtheꢀSpecialꢀFunctionꢀRegisterꢀsection.
Rev. 0.00
17
�eꢀteꢁꢂeꢃ ꢄꢅꢆ ꢄ01ꢄ
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
