HT45F12
8-Bit Flash MCU with Op Amps & Comparators
Stack
ThisꢀisꢀaꢀspecialꢀpartꢀofꢀtheꢀmemoryꢀwhichꢀisꢀusedꢀtoꢀsaveꢀtheꢀcontentsꢀofꢀtheꢀProgramꢀCounterꢀ
only.ꢀTheꢀstackꢀisꢀorganizedꢀintoꢀ4ꢀlevelsꢀandꢀneitherꢀpartꢀofꢀtheꢀdataꢀnorꢀpartꢀofꢀtheꢀprogramꢀspace,ꢀ
andꢀisꢀneitherꢀreadableꢀnorꢀwriteable.ꢀTheꢀactivatedꢀlevelꢀisꢀindexedꢀbyꢀtheꢀStackꢀPointer,ꢀandꢀisꢀ
neitherꢀreadableꢀnorꢀwriteable.ꢀAtꢀaꢀsubroutineꢀcallꢀorꢀinterruptꢀacknowledgeꢀsignal,ꢀtheꢀcontentsꢀofꢀ
theꢀProgramꢀCounterꢀareꢀpushedꢀontoꢀtheꢀstack.ꢀAtꢀtheꢀendꢀofꢀaꢀsubroutineꢀorꢀanꢀinterruptꢀroutine,ꢀ
signaledꢀbyꢀaꢀreturnꢀinstruction,ꢀRETꢀorꢀRETI,ꢀtheꢀProgramꢀCounterꢀisꢀrestoredꢀtoꢀitsꢀpreviousꢀvalueꢀ
fromꢀtheꢀstack.ꢀAfterꢀaꢀdeviceꢀreset,ꢀtheꢀStackꢀPointerꢀwillꢀpointꢀtoꢀtheꢀtopꢀofꢀtheꢀstack.
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Ifꢀtheꢀstackꢀisꢀfullꢀandꢀanꢀenabledꢀinterruptꢀtakesꢀplace,ꢀtheꢀinterruptꢀrequestꢀflagꢀwillꢀbeꢀrecordedꢀ
butꢀtheꢀacknowledgeꢀsignalꢀwillꢀbeꢀinhibited.ꢀWhenꢀtheꢀStackꢀPointerꢀisꢀdecremented,ꢀbyꢀRETꢀorꢀ
RETI,ꢀtheꢀinterruptꢀwillꢀbeꢀserviced.ꢀThisꢀfeatureꢀpreventsꢀstackꢀoverflowꢀallowingꢀtheꢀprogrammerꢀ
toꢀuseꢀtheꢀstructureꢀmoreꢀeasily.ꢀHowever,ꢀwhenꢀtheꢀstackꢀisꢀfull,ꢀaꢀCALLꢀsubroutineꢀinstructionꢀcanꢀ
stillꢀbeꢀexecutedꢀwhichꢀwillꢀresultꢀinꢀaꢀstackꢀoverflow.ꢀPrecautionsꢀshouldꢀbeꢀtakenꢀtoꢀavoidꢀsuchꢀ
casesꢀwhichꢀmightꢀcauseꢀunpredictableꢀprogramꢀbranching.ꢀIfꢀtheꢀstackꢀisꢀoverflow,ꢀtheꢀfirstꢀProgramꢀ
Counterꢀsaveꢀinꢀtheꢀstackꢀwillꢀbeꢀlost.
Arithmetic and Logic Unit – ALU
Theꢀarithmetic-logicꢀunitꢀorꢀALUꢀisꢀaꢀcriticalꢀareaꢀofꢀtheꢀmicrocontrollerꢀthatꢀcarriesꢀoutꢀarithmeticꢀ
andꢀlogicꢀoperationsꢀofꢀtheꢀinstructionꢀset.ꢀConnectedꢀtoꢀtheꢀmainꢀmicrocontrollerꢀdataꢀbus,ꢀtheꢀALUꢀ
receivesꢀrelatedꢀinstructionꢀcodesꢀandꢀperformsꢀtheꢀrequiredꢀarithmeticꢀorꢀlogicalꢀoperationsꢀafterꢀ
whichꢀtheꢀresultꢀwillꢀbeꢀplacedꢀinꢀtheꢀspecifiedꢀregister.ꢀAsꢀtheseꢀALUꢀcalculationꢀorꢀoperationsꢀmayꢀ
resultꢀinꢀcarry,ꢀborrowꢀorꢀotherꢀstatusꢀchanges,ꢀtheꢀstatusꢀregisterꢀwillꢀbeꢀcorrespondinglyꢀupdatedꢀtoꢀ
reflectꢀtheseꢀchanges.ꢀTheꢀALUꢀsupportsꢀtheꢀfollowingꢀfunctions:
•ꢀ Arithmeticꢀoperations:ꢀADD,ꢀADDM,ꢀADC,ꢀADCM,ꢀSUB,ꢀSUBM,ꢀSBC,ꢀSBCM,ꢀDAA
•ꢀ Logicꢀoperations:ꢀAND,ꢀOR,ꢀXOR,ꢀANDM,ꢀORM,ꢀXORM,ꢀCPL,ꢀCPLA
•ꢀ RotationꢀRRA,ꢀRR,ꢀRRCA,ꢀRRC,ꢀRLA,ꢀRL,ꢀRLCA,ꢀRLC
•ꢀ IncrementꢀandꢀDecrementꢀINCA,ꢀINC,ꢀDECA,ꢀDEC
•ꢀ Branchꢀdecision,ꢀJMP,ꢀSZ,ꢀSZA,ꢀSNZ,ꢀSIZ,ꢀSDZ,ꢀSIZA,ꢀSDZA,ꢀCALL,ꢀRET,ꢀRETI.
Rev. 0.00
18
�eꢀteꢁꢂeꢃ ꢄꢅꢆ ꢄ01ꢄ
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
