HT66F018 datasheet(21/154 Pages) HOLTEK

21 / 154 page

Rev. 1.70

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HT66F018

A/D Flash MCU with EEPROM

HT66F018

A/D Flash MCU with EEPROM

Stack

ThisisaspecialpartofthememorywhichisusedtosavethecontentsoftheProgramCounter

only.Thestackisorganizedinto8levelsandneitherpartofthedatanorpartoftheprogramspace,

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.

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

HT66F018 Datasheet(PDF) 21 Page - Holtek Semiconductor Inc