HT45F77 datasheet(37/203 Pages) HOLTEK

37 / 203 page

Rev. 1.20

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HT45F77

Body Fat Scale Flash MCU

HT45F77

Body Fat Scale Flash MCU

Accumulator – ACC

TheAccumulatoriscentraltotheoperationofanymicrocontrollerandiscloselyrelatedwith

operationscarriedoutbytheALU.TheAccumulatoristheplacewhereallintermediateresults

fromtheALUarestored.WithouttheAccumulatoritwouldbenecessarytowritetheresultof

eachcalculationorlogicaloperationsuchasaddition,subtraction,shift,etc.,totheDataMemory

resultinginhigherprogrammingandtimingoverheads.Datatransferoperationsusuallyinvolve

thetemporarystoragefunctionoftheAccumulator;forexample,whentransferringdatabetween

oneuserdefinedregisterandanother,itisnecessarytodothisbypassingthedatathroughthe

Accumulatorasnodirecttransferbetweentworegistersispermitted.

Program Counter Low Register – PCL

Toprovideadditionalprogramcontrolfunctions,thelowbyteoftheProgramCounterismade

accessibletoprogrammersbylocatingitwithintheSpecialPurposeareaoftheDataMemory.By

manipulatingthisregister,directjumpstootherprogramlocationsareeasilyimplemented.Loading

avaluedirectlyintothisPCLregisterwillcauseajumptothespecifiedProgramMemorylocation,

however,astheregisterisonly8-bitwide,onlyjumpswithinthecurrentProgramMemorypageare

permitted.Whensuchoperationsareused,notethatadummycyclewillbeinserted.

Look-up Table Registers – TBLP, TBHP, TBLH

Thesethreespecialfunctionregistersareusedtocontroloperationofthelook-uptablewhichis

storedintheProgramMemory.TBLPandTBHParethetablepointerandindicatesthelocation

wherethetabledataislocated.Theirvaluemustbesetupbeforeanytablereadcommandsare

executed.Theirvaluecanbechanged,forexampleusingthe"INC"or"DEC"instructions,allowing

foreasytabledatapointingandreading.TBLHisthelocationwherethehighorderbyteofthetable

dataisstoredafteratablereaddatainstructionhasbeenexecuted.Notethatthelowerordertable

databyteistransferredtoauserdefinedlocation.

Status Register – STATUS

This8-bitregistercontainstheSCflag,CZflag,zeroflag(Z),carryflag(C),auxiliarycarryflag(AC),

overflowflag(OV),powerdownflag(PDF),andwatchdogtime-outflag(TO).Thesearithmetic/

logicaloperationandsystemmanagementflagsareusedtorecordthestatusandoperationofthe

microcontroller.

WiththeexceptionoftheTOandPDFflags,bitsinthestatusregistercanbealteredbyinstructions

likemostotherregisters.AnydatawrittenintothestatusregisterwillnotchangetheTOorPDFflag.

Inaddition,operationsrelatedtothestatusregistermaygivedifferentresultsduetothedifferent

instructionoperations.TheTOflagcanbeaffectedonlybyasystempower-up,aWDTtime-outor

byexecutingthe"CLRWDT"or"HALT"instruction.ThePDFflagisaffectedonlybyexecuting

the"HALT"or"CLRWDT"instructionorduringasystempower-up.

TheZ,OV,AC,C,SCandCZflagsgenerallyreflectthestatusofthelatestoperations.

• Cissetifanoperationresultsinacarryduringanadditionoperationorifaborrowdoesnottake

placeduringasubtractionoperation;otherwiseCiscleared.Cisalsoaffectedbyarotatethrough

carryinstruction.

• ACissetifanoperationresultsinacarryoutofthelownibblesinaddition,ornoborrowfrom

thehighnibbleintothelownibbleinsubtraction;otherwiseACiscleared.

• Zissetiftheresultofanarithmeticorlogicaloperationiszero;otherwiseZiscleared.

• OVissetifanoperationresultsinacarryintothehighest-orderbitbutnotacarryoutofthe

highest-orderbit,orviceversa;otherwiseOViscleared.

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