HT45F3W datasheet(20/167 Pages) HOLTEK

20 / 167 page

Rev. 1.50

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HT45F3W

R-Type Blood Pressure Meter Flash MCU

HT45F3W

R-Type Blood Pressure Meter Flash MCU

Stack

ThisisaspecialpartofthememorywhichisusedtosavethecontentsoftheProgramCounteronly.

Thestackisorganizedinto12levelsandneitherpartofthedatanorpartoftheprogramspace,

andisneitherreadablenorwriteable.TheactivatedlevelisindexedbytheStackPointer,andis

neitherreadablenorwriteable.Atasubroutinecallorinterruptacknowledgesignal,thecontentsof

theProgramCounterarepushedontothestack.Attheendofasubroutineoraninterruptroutine,

signaledbyareturninstruction,RETorRETI,theProgramCounterisrestoredtoitspreviousvalue

fromthestack.Afteradevicereset,theStackPointerwillpointtothetopofthestack.

Ifthestackisfullandanenabledinterrupttakesplace,theinterruptrequestflagwillberecordedbut

theacknowledgesignalwillbeinhibited.WhentheStackPointerisdecremented,byRETorRETI,

theinterruptwillbeserviced.Thisfeaturepreventsstackoverflowallowingtheprogrammertouse

thestructuremoreeasily.However,whenthestackisfull,aCALLsubroutineinstructioncanstill

beexecutedwhichwillresultinastackoverflow.Precautionsshouldbetakentoavoidsuchcases

whichmightcauseunpredictableprogrambranching.

Ifthestackisoverflow,thefirstProgramCountersaveinthestackwillbelost.

Pr og ra m Co un te r

St ac k Le ve l 1

St ac k Le ve l 2

St ac k Le ve l 3

St ac k Le ve l 12

Pr og ra m

Me mo ry

T op of S ta ck

St ac k

Po in te r

Bo tt om o f St ac k

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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