HT45FH4M
Lithium Battery Backup Power ASSP MCU
Status Register – STATUS
Thisꢀ8-bitꢀregisterꢀcontainsꢀtheꢀzeroꢀflagꢀ(Z),ꢀcarryꢀflagꢀ(C),ꢀauxiliaryꢀcarryꢀflagꢀ(AC),ꢀoverflowꢀflagꢀ
(OV),ꢀpowerꢀdownꢀflagꢀ(PDF),ꢀandꢀwatchdogꢀtime-outꢀflagꢀ(TO).ꢀTheseꢀarithmetic/logicalꢀoperationꢀ
andꢀsystemꢀmanagementꢀflagsꢀareꢀusedꢀtoꢀrecordꢀtheꢀstatusꢀandꢀoperationꢀofꢀtheꢀmicrocontroller.ꢀ
WithꢀtheꢀexceptionꢀofꢀtheꢀTOꢀandꢀPDFꢀflags,ꢀbitsꢀinꢀtheꢀstatusꢀregisterꢀcanꢀbeꢀalteredꢀbyꢀinstructionsꢀ
likeꢀmostꢀotherꢀregisters.ꢀAnyꢀdataꢀwrittenꢀintoꢀtheꢀstatusꢀregisterꢀwillꢀnotꢀchangeꢀtheꢀTOꢀorꢀPDFꢀflag.ꢀ
Inꢀaddition,ꢀoperationsꢀrelatedꢀtoꢀtheꢀstatusꢀregisterꢀmayꢀgiveꢀdifferentꢀresultsꢀdueꢀtoꢀtheꢀdifferentꢀ
instructionꢀoperations.ꢀTheꢀTOꢀflagꢀcanꢀbeꢀaffectedꢀonlyꢀbyꢀaꢀsystemꢀpower-up,ꢀaꢀWDTꢀtime-outꢀorꢀ
byꢀexecutingꢀtheꢀ“CLRꢀWDT”ꢀorꢀ“HALT”ꢀinstruction.ꢀTheꢀPDFꢀflagꢀisꢀaffectedꢀonlyꢀbyꢀexecutingꢀ
theꢀ“HALT”ꢀorꢀ“CLRꢀWDT”ꢀinstructionꢀorꢀduringꢀaꢀsystemꢀpower-up.
TheꢀZ,ꢀOV,ꢀACꢀandꢀCꢀflagsꢀgenerallyꢀreflectꢀtheꢀstatusꢀofꢀtheꢀlatestꢀoperations.
•ꢀ Cꢀisꢀsetꢀifꢀanꢀoperationꢀresultsꢀinꢀaꢀcarryꢀduringꢀanꢀadditionꢀoperationꢀorꢀifꢀaꢀborrowꢀdoesꢀnotꢀtakeꢀ
placeꢀduringꢀaꢀsubtractionꢀoperation;ꢀotherwiseꢀCꢀisꢀcleared.ꢀCꢀisꢀalsoꢀaffectedꢀbyꢀaꢀrotateꢀthroughꢀ
carryꢀinstruction.
•ꢀ ACꢀisꢀsetꢀifꢀanꢀoperationꢀresultsꢀinꢀaꢀcarryꢀoutꢀofꢀtheꢀlowꢀnibblesꢀinꢀaddition,ꢀorꢀnoꢀborrowꢀfromꢀ
theꢀhighꢀnibbleꢀintoꢀtheꢀlowꢀnibbleꢀinꢀsubtraction;ꢀotherwiseꢀACꢀisꢀcleared.ꢀ
•ꢀ Zꢀisꢀsetꢀifꢀtheꢀresultꢀofꢀanꢀarithmeticꢀorꢀlogicalꢀoperationꢀisꢀzero;ꢀotherwiseꢀZꢀisꢀcleared.
•ꢀ OVꢀisꢀsetꢀifꢀanꢀoperationꢀresultsꢀinꢀaꢀcarryꢀintoꢀtheꢀhighest-orderꢀbitꢀbutꢀnotꢀaꢀcarryꢀoutꢀofꢀtheꢀ
highest-orderꢀbit,ꢀorꢀviceꢀversa;ꢀotherwiseꢀOVꢀisꢀcleared.ꢀ
•ꢀ PDFꢀisꢀclearedꢀbyꢀaꢀsystemꢀpower-upꢀorꢀexecutingꢀtheꢀ“CLRꢀWDT”ꢀinstruction.ꢀPDFꢀisꢀsetꢀbyꢀ
executingꢀtheꢀ“HALT”ꢀinstruction.
•ꢀ TOꢀisꢀclearedꢀbyꢀaꢀsystemꢀpower-upꢀorꢀexecutingꢀtheꢀ“CLRꢀWDT”ꢀorꢀ“HALT”ꢀinstruction.ꢀTOꢀisꢀ
setꢀbyꢀaꢀWDTꢀtime-out.
Inꢀaddition,ꢀonꢀenteringꢀanꢀinterruptꢀsequenceꢀorꢀexecutingꢀaꢀsubroutineꢀcall,ꢀtheꢀstatusꢀregisterꢀwillꢀ
notꢀbeꢀpushedꢀontoꢀtheꢀstackꢀautomatically.ꢀIfꢀtheꢀcontentsꢀofꢀtheꢀstatusꢀregistersꢀareꢀimportantꢀandꢀifꢀ
theꢀsubroutineꢀcanꢀcorruptꢀtheꢀstatusꢀregister,ꢀprecautionsꢀmustꢀbeꢀtakenꢀtoꢀcorrectlyꢀsaveꢀit.
Rev. 1.10
ꢅꢃ
�anꢀaꢁꢂ 1ꢃꢄ ꢅ01ꢆ
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
