HT45F3420 datasheet(21/141 Pages) HOLTEK

21 / 141 page

Rev. 1.31

April 11, 2017

Rev. 1.31

April 11, 2017

HT45F3420/HT45F3430

Personal Care Flash MCU

HT45F3420/HT45F3430

Personal Care Flash MCU

ThelowerbyteoftheProgramCounter,knownastheProgramCounterLowregisterorPCL,is

availableforprogramcontrolandisareadableandwriteableregister.Bytransferringdatadirectly

intothisregister,ashortprogramjumpcanbeexecuteddirectly,however,asonlythislowbyte

isavailableformanipulation,thejumpsarelimitedtothepresentpageofmemory,thatis256

locations.Whensuchprogramjumpsareexecuteditshouldalsobenotedthatadummycycle

willbeinserted.ManipulatingthePCLregistermaycauseprogrambranching,soanextracycleis

neededtopre-fetch.

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 og ra m Co un te r

St ac k Le ve l 1

St ac k Le ve l 4

Pr og ra m

Me mo ry

T op o f S ta ck

St ac k

Po in te r

Bo tt om o f St ac k

St ac k Le ve l 2

St ac k Le ve l 3

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

HT45F3420 Datasheet(PDF) 21 Page - Holtek Semiconductor Inc

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