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Rev. 2.50 42 June 22, 2017 Rev. 2.50 43 June 22, 2017

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60

HT66FU30/HT66FU40/HT66FU50/HT66FU60

A/D Flash MCU with EEPROM

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60

HT66FU30/HT66FU40/HT66FU50/HT66FU60

A/D Flash MCU with EEPROM

Status Register – STATUS

This8-bitregistercontainsthezeroag(Z),carryag(C),auxiliarycarryag(AC),overowag

(OV),powerdownag(PDF),andwatchdogtime-outag(TO).Thesearithmetic/logicaloperation

andsystemmanagementagsareusedtorecordthestatusandoperationofthemicrocontroller.

WiththeexceptionoftheTOandPDFags,bitsinthestatusregistercanbealteredbyinstructions

likemostotherregisters.AnydatawrittenintothestatusregisterwillnotchangetheTOorPDFag.

Inaddition,operationsrelatedtothestatusregistermaygivedifferentresultsduetothedifferent

instructionoperations.TheTOagcanbeaffectedonlybyasystempower-up,aWDTtime-outor

byexecutingthe"CLRWDT"or"HALT"instruction.ThePDFagisaffectedonlybyexecuting

the"HALT"or"CLRWDT"instructionorduringasystempower-up.

TheZ,OV,ACandCagsgenerallyreectthestatusofthelatestoperations.

• Cissetifanoperationresultsinacarryduringanadditionoperationorifaborrowdoesnottake

placeduringasubtractionoperation;otherwiseCiscleared.Cisalsoaffectedbyarotatethrough

carryinstruction.

• ACissetifanoperationresultsinacarryoutofthelownibblesinaddition,ornoborrowfrom

thehighnibbleintothelownibbleinsubtraction;otherwiseACiscleared.

• Zissetiftheresultofanarithmeticorlogicaloperationiszero;otherwiseZiscleared.

• OVissetifanoperationresultsinacarryintothehighest-orderbitbutnotacarryoutofthe

highest-orderbit,orviceversa;otherwiseOViscleared.

• PDFisclearedbyasystempower-uporexecutingthe“CLRWDT”instruction.PDFissetby

executingthe“HALT”instruction.

• TOisclearedbyasystempower-uporexecutingthe“CLRWDT”or“HALT”instruction.TOis

setbyaWDTtime-out.

Inaddition,onenteringaninterruptsequenceorexecutingasubroutinecall,thestatusregisterwill

notbepushedontothestackautomatically.Ifthecontentsofthestatusregistersareimportantandif

thesubroutinecancorruptthestatusregister,precautionsmustbetakentocorrectlysaveit.

Holtek HT66F30 User Manual

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