HT82B42RE datasheet(45/84 Pages) HOLTEK

45 / 84 page

Rev. 1.10

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Rev. 1.10

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HT82B42R/HT82B42RE

I/O MCU with USB Interface

Standby Current Considerations

AsthemainreasonforenteringthePowerDownModeistokeepthecurrentconsumptionofthe

microcontrollertoaslowavalueaspossible,perhapsonlyintheorderofseveralmicro-amps,there

areotherconsiderationswhichmustalsobetakenintoaccountbythecircuitdesignerifthepower

consumptionistobeminimised.

SpecialattentionmustbemadetotheI/Opinsonthedevice.Allhigh-impedanceinputpinsmust

beconnectedtoeitherafixedhighorlowlevelasanyfloatinginputpinscouldcreateinternal

oscillationsandresultinincreasedcurrentconsumption.Caremustalsobetakenwiththeloads,

whichareconnectedtoI/Opins,whicharesetupasoutputs.Theseshouldbeplacedinacondition

inwhichminimumcurrentisdrawnorconnectedonlytoexternalcircuitsthatdonotdrawcurrent,

suchasotherCMOSinputs.

IftheconfigurationoptionshaveenabledtheWatchdogTimerinternaloscillatorthenthiswill

continuetorunwheninthePowerDownModeandwillthusconsumesomepower.Forpower

sensitiveapplicationsitmaybethereforepreferabletousethesystemclocksourcefortheWatchdog

Timer.

Wake-up

AfterthesystementersthePowerDownMode,itcanbewokenupfromoneofvarioussources

listedasfollows:

• Anexternalreset

• AnexternalfallingedgeWake-up

• Asysteminterrupt

• AWDToverflow

Ifthesystemiswokenupbyanexternalreset,thedevicewillexperienceafullsystemreset,

however,ifthedeviceiswokenupbyaWDToverflow,aWatchdogTimerresetwillbeinitiated.

Althoughbothofthesewake-upmethodswillinitiatearesetoperation,theactualsourceofthe

wake-upcanbedeterminedbyexaminingtheTOandPDFflags.ThePDFflagisclearedbya

systempower-uporexecutingtheclearWatchdogTimerinstructionsandissetwhenexecutingthe

"HALT"instruction.TheTOflagissetifaWDTtime-outoccurs,andcausesawake-upthatonly

resetstheProgramCounterandStackPointer,theotherflagsremainintheiroriginalstatus.

Eachpincanbesetupviaanindividualconfigurationoptiontopermitanegativetransitiononthe

pintowake-upthesystem.Whenapinwake-upoccurs,theprogramwillresumeexecutionatthe

instructionfollowingthe"HALT"instruction.

Ifthesystemiswokenupbyaninterrupt,thentwopossiblesituationsmayoccur.Thefirstiswhere

therelatedinterruptisdisabledortheinterruptisenabledbutthestackisfull,inwhichcasethe

programwillresumeexecutionattheinstructionfollowingthe"HALT"instruction.Inthissituation,

theinterruptwhichwoke-upthedevicewillnotbeimmediatelyserviced,butwillratherbeserviced

laterwhentherelatedinterruptisfinallyenabledorwhenastacklevelbecomesfree.Theother

situationiswheretherelatedinterruptisenabledandthestackisnotfull,inwhichcasetheregular

interruptresponsetakesplace.Ifaninterruptrequestflagissetto"1"beforeenteringthePower

DownMode,thewake-upfunctionoftherelatedinterruptwillbedisabled.

Nomatterwhatthesourceofthewake-upeventis,onceawake-upsituationoccurs,atimeperiod

equalto1024systemclockperiodswillberequiredbeforenormalsystemoperationresumes.

However,ifthewake-uphasoriginatedduetoaninterrupt,theactualinterruptsubroutineexecution

willbedelayedbyanadditionaloneormorecycles.Ifthewake-upresultsintheexecutionofthe

nextinstructionfollowingthe"HALT"instruction,thiswillbeexecutedimmediatelyafterthe1024

systemclockperioddelayhasended.

HT82B42RE Datasheet(PDF) 45 Page - Holtek Semiconductor Inc

HT82B42RE Datasheet(HTML) 45 Page - Holtek Semiconductor Inc

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