HT45FH4M
Lithium Battery Backup Power ASSP MCU
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System Clock and Pipelining
Forꢀinstructionsꢀinvolvingꢀbranches,ꢀsuchꢀasꢀjumpꢀorꢀcallꢀinstructions,ꢀtwoꢀmachineꢀcyclesꢀareꢀ
requiredꢀtoꢀcompleteꢀinstructionꢀexecution.ꢀAnꢀextraꢀcycleꢀisꢀrequiredꢀasꢀtheꢀprogramꢀtakesꢀoneꢀ
cycleꢀtoꢀfirstꢀobtainꢀtheꢀactualꢀjumpꢀorꢀcallꢀaddressꢀandꢀthenꢀanotherꢀcycleꢀtoꢀactuallyꢀexecuteꢀtheꢀ
branch.ꢀTheꢀrequirementꢀforꢀthisꢀextraꢀcycleꢀshouldꢀbeꢀtakenꢀintoꢀaccountꢀbyꢀprogrammersꢀinꢀtimingꢀ
sensitiveꢀapplications.
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Instruction Fetching
Program Counter
Duringꢀprogramꢀexecution,ꢀtheꢀProgramꢀCounterꢀisꢀusedꢀtoꢀkeepꢀtrackꢀofꢀtheꢀaddressꢀofꢀtheꢀ
nextꢀinstructionꢀtoꢀbeꢀexecuted.ꢀItꢀisꢀautomaticallyꢀincrementedꢀbyꢀoneꢀeachꢀtimeꢀanꢀinstructionꢀ
isꢀexecutedꢀexceptꢀforꢀinstructions,ꢀsuchꢀasꢀ“JMP”ꢀorꢀ“CALL”ꢀthatꢀdemandꢀaꢀjumpꢀtoꢀaꢀnon-
consecutiveꢀProgramꢀMemoryꢀaddress.ꢀOnlyꢀtheꢀlowerꢀ8ꢀbits,ꢀknownꢀasꢀtheꢀProgramꢀCounterꢀLowꢀ
Register,ꢀareꢀdirectlyꢀaddressableꢀbyꢀtheꢀapplicationꢀprogram.
Whenꢀexecutingꢀinstructionsꢀrequiringꢀjumpsꢀtoꢀnon-consecutiveꢀaddressesꢀsuchꢀasꢀaꢀjumpꢀinstruction,ꢀ
aꢀsubroutineꢀcall,ꢀinterruptꢀorꢀreset,ꢀetc.,ꢀtheꢀmicrocontrollerꢀmanagesꢀprogramꢀcontrolꢀbyꢀloadingꢀtheꢀ
requiredꢀaddressꢀintoꢀtheꢀProgramꢀCounter.ꢀForꢀconditionalꢀskipꢀinstructions,ꢀonceꢀtheꢀconditionꢀhasꢀ
beenꢀmet,ꢀtheꢀnextꢀinstruction,ꢀwhichꢀhasꢀalreadyꢀbeenꢀfetchedꢀduringꢀtheꢀpresentꢀinstructionꢀexecution,ꢀ
isꢀdiscardedꢀandꢀaꢀdummyꢀcycleꢀtakesꢀitsꢀplaceꢀwhileꢀtheꢀcorrectꢀinstructionꢀisꢀobtained.
Program Counter
Program Counter High byte
PCL Register
PC10~PC8
PCL7~PCL0
Rev. 1.10
1ꢃ
�anꢀaꢁꢂ 1ꢃꢄ ꢅ01ꢆ
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
