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HT46R0042 Datasheet(PDF) 12 Page - Holtek Semiconductor Inc |
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HT46R0042 Datasheet(HTML) 12 Page - Holtek Semiconductor Inc |
12 / 83 page Rev. 1.00 1� ��to�e� ��� �01� Rev. 1.00 13 ��to�e� ��� �01� HT46R0042 Cost-Effective A/D 8-Bit OTP MCU HT46R0042 Cost-Effective A/D 8-Bit OTP MCU Program Counter – PC Duringprogramexecution,theProgramCounterisusedtokeeptrackoftheaddressofthe nextinstructiontobeexecuted.Itisautomaticallyincrementedbyoneeachtimeaninstruction isexecutedexceptforinstructions,suchas“JMP”or“CALL”thatdemandajumptoanon- consecutiveProgramMemoryaddress.Itmustbenotedthatonlythelower8bits,knownasthe ProgramCounterLowRegister,aredirectlyaddressablebyuser. Whenexecutinginstructionsrequiringjumpingtonon-consecutiveaddressessuchasajump instruction,asubroutinecall,interruptorreset,etc,themicrocontrollermanagesprogramcontrol byloadingtherequiredaddressintotheProgramCounter.Forconditionalskipinstructions,once theconditionhasbeenmet,thenextinstruction,whichhasalreadybeenfetchedduringthepresent instructionexecution,isdiscardedandadummycycletakesitsplacewhilethecorrectinstructionis obtained. Program Counter High Byte of Program Low Byte of Program PC10~PC8 PCL�~PCL0 ThelowerbyteoftheProgramCounter,knownastheProgramCounterLowregisterorPCL,is availableforprogramcontrolandisareadableandwriteableregister.Bytransferringdatadirectly intothisregister,ashortprogramjumpcanbeexecuteddirectly.However,asonlythislowbyte isavailableformanipulation,thejumpsarelimitedinthepresentpageofmemory,whichhave 256locations.Whensuchprogramjumpsareexecuteditshouldalsobenotedthatadummycycle willbeinserted.ThelowerbyteoftheProgramCounterisfullyaccessibleunderprogramcontrol. ManipulatingthePCLmightcauseprogrambranching,soanextracycleisneededtopre-fetch. Stack ThisisaspecialpartofthememorywhichisusedtosavethecontentsoftheProgramCounteronly. Thedevicestackisorganizedinto4levelsandneitherpartofthedatanorpartoftheprogramspace, andisneitherreadablenorwriteable.TheactivatedlevelisindexedbytheStackPointer,andis neitherreadablenorwriteable.Atasubroutinecallorinterruptacknowledgesignal,thecontentsof theProgramCounterarepushedontothestack.Attheendofasubroutineoraninterruptroutine, signaledbyareturninstruction,RETorRETI,theProgramCounterisrestoredtoitspreviousvalue fromthestack.Afteradevicereset,theStackPointerwillpointtothetopofthestack. Pr ogr am C ount er St a ck Lev el 1 St a ck Lev el 2 St a ck Lev el 3 St a ck Lev el 4 Pr ogr am Me mo ry To p of S ta ck St ac k Po in te r Bo tt om o f St ac k Ifthestackisfullandanenabledinterrupttakesplace,theinterruptrequestflagwillberecordedbut theacknowledgesignalwillbeinhibited.WhentheStackPointerisdecremented,byRETorRETI, theinterruptwillbeserviced.Thisfeaturepreventsstackoverflowallowingtheprogrammertouse thestructuremoreeasily.However,whenthestackisfull,aCALLsubroutineinstructioncanstill beexecutedwhichwillresultinastackoverflow.Precautionsshouldbetakentoavoidsuchcases whichmightcauseunpredictableprogrambranching. |
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