HT45F2020 datasheet(14/85 Pages) HOLTEK

14 / 85 page

Rev. 1.00

April 11, 2017

Rev. 1.00

April 11, 2017

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

ThelowerbyteoftheProgramCounter,knownastheProgramCounterLowregisterorPCL,is

availableforprogramcontrolandisareadableandwriteableregister.Bytransferringdatadirectly

intothisregister,ashortprogramjumpcanbeexecuteddirectly.However,asonlythislowbyte

isavailableformanipulation,thejumpsarelimitedtothepresentpageofmemorythatis256

locations.Whensuchprogramjumpsareexecuteditshouldalsobenotedthatadummycycle

willbeinserted.ManipulatingthePCLregistermaycauseprogrambranching,soanextracycleis

neededtopre-fetch.

Stack

ThisisaspecialpartofthememorywhichisusedtosavethecontentsoftheProgramCounter

only.Thestackisorganizedinto2levelsandneitherpartofthedatanorpartoftheprogramspace,

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.

Stack

Pointer

Stack Level 2

Stack Level 1

Program Memory

Program Counter

Bottom of Stack

Top of Stack

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

• Rotation:RRA,RR,RRCA,RRC,RLA,RL,RLCA,RLC

• IncrementandDecrement:INCA,INC,DECA,DEC

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

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