HT45F4M datasheet(16/138 Pages) HOLTEK

16 / 138 page

Rev. 1.10

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Rev. 1.10

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HT45F4M

Lithium Battery Backup Power ASSP MCU

HT45F4M

Lithium Battery Backup Power ASSP MCU

Stack

ThisisaspecialpartofthememorywhichisusedtosavethecontentsoftheProgramCounter

only.Thestackisneitherpartofthedatanorpartoftheprogramspace,andisneitherreadablenor

writeable.TheactivatedlevelisindexedbytheStackPointer,andisneitherreadablenorwriteable.

Atasubroutinecallorinterruptacknowledgesignal,thecontentsoftheProgramCounterarepushed

ontothestack.Attheendofasubroutineoraninterruptroutine,signaledbyareturninstruction,

RETorRETI,theProgramCounterisrestoredtoitspreviousvaluefromthestack.Afteradevice

reset,theStackPointerwillpointtothetopofthestack.

Ifthestackisfullandanenabledinterrupttakesplace,theinterruptrequestflagwillberecorded

buttheacknowledgesignalwillbeinhibited.WhentheStackPointerisdecremented,byRETor

RETI,theinterruptwillbeserviced.Thisfeaturepreventsstackoverflowallowingtheprogrammer

tousethestructuremoreeasily.However,whenthestackisfull,aCALLsubroutineinstructioncan

stillbeexecutedwhichwillresultinastackoverflow.Precautionsshouldbetakentoavoidsuch

caseswhichmightcauseunpredictableprogrambranching.Ifthestackisoverflow,thefirstProgram

Countersaveinthestackwillbelost.

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

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Me mo ry

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St ac k

Po in te r

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Arithmetic and Logic Unit – ALU

Thearithmetic-logicunitorALUisacriticalareaofthemicrocontrollerthatcarriesoutarithmetic

andlogicoperationsoftheinstructionset.Connectedtothemainmicrocontrollerdatabus,theALU

receivesrelatedinstructioncodesandperformstherequiredarithmeticorlogicaloperationsafter

whichtheresultwillbeplacedinthespecifiedregister.AstheseALUcalculationoroperationsmay

resultincarry,borroworotherstatuschanges,thestatusregisterwillbecorrespondinglyupdatedto

reflectthesechanges.TheALUsupportsthefollowingfunctions:

• Arithmeticoperations:ADD,ADDM,ADC,ADCM,SUB,SUBM,SBC,SBCM,DAA

• Logicoperations:AND,OR,XOR,ANDM,ORM,XORM,CPL,CPLA

• RotationRRA,RR,RRCA,RRC,RLA,RL,RLCA,RLC

• IncrementandDecrementINCA,INC,DECA,DEC

• Branchdecision,JMP,SZ,SZA,SNZ,SIZ,SDZ,SIZA,SDZA,CALL,RET,RETI

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