HT45F2020 datasheet(32/85 Pages) HOLTEK

32 / 85 page

Rev. 1.00

April 11, 2017

Rev. 1.00

April 11, 2017

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

Standby Current Considerations

AsthemainreasonforenteringtheSLEEPorIDLEModeistokeepthecurrentconsumptionofthe

devicetoaslowavalueaspossible,perhapsonlyintheorderofseveralmicro-ampsexceptinthe

IDLE1andIDLE2Mode,thereareotherconsiderationswhichmustalsobetakenintoaccountby

thecircuitdesignerifthepowerconsumptionistobeminimised.Specialattentionmustbemade

totheI/Opinsonthedevice.Allhigh-impedanceinputpinsmustbeconnectedtoeitherafixed

highorlowlevelasanyfloatinginputpinscouldcreateinternaloscillationsandresultinincreased

currentconsumption.Thesemusteitherbesetupasoutputsorifsetupasinputsmusthavepull-high

resistorsconnected.

Caremustalsobetakenwiththeloads,whichareconnectedtoI/Opins,whicharesetupasoutputs.

Theseshouldbeplacedinaconditioninwhichminimumcurrentisdrawnorconnectedonlyto

externalcircuitsthatdonotdrawcurrent,suchasotherCMOSinputs.Alsonotethatadditional

standbycurrentwillalsoberequirediftheLIRCoscillatorhasenabled.

IntheIDLE1andIDLE2Modethehighspeedoscillatorison,iftheperipheralfunctionclock

sourceisderivedfromthehighspeedoscillator,theadditionalstandbycurrentwillalsobeperhaps

intheorderofseveralhundredmicro-amps.

Wake-up

TominimisepowerconsumptionthedevicecanentertheSLEEPoranyIDLEMode,wherethe

CPUwillbeswitchedoff.However,whenthedeviceiswokenupagain,itwilltakeaconsiderable

timefortheoriginalsystemoscillatortorestart,stabliseandallownormaloperationtoresume.

AfterthesystementerstheSLEEPorIDLEMode,itcanbewokenupfromoneofvarioussources

listedasfollows:

• AnexternalfallingedgeonPortA

• Asysteminterrupt

• AWDToverflow

Whenthedeviceexecutesthe“HALT”instruction,thePDFflagwillbesetto1.ThePDFflagwill

beclearedto0ifthedeviceexperiencesasystempower-uporexecutestheclearWatchdogTimer

instruction.IfthesystemiswokenupbyaWDToverflow,aWatchdogTimerresetwillbeinitiated

andtheTOflagwillbesetto1.TheTOflagissetifaWDTtime-outoccursandcausesawake-up

thatonlyresetstheProgramCounterandStackPointer,otherflagsremainintheiroriginalstatus.

EachpinonPortAcanbesetupusingthePAWUregistertopermitanegativetransitiononthepin

towakeupthesystem.WhenaPortApinwake-upoccurs,theprogramwillresumeexecutionat

theinstructionfollowingthe“HALT”instruction.Ifthesystemiswokenupbyaninterrupt,then

twopossiblesituationsmayoccur.Thefirstiswheretherelatedinterruptisdisabledortheinterrupt

isenabledbutthestackisfull,inwhichcasetheprogramwillresumeexecutionattheinstruction

followingthe“HALT”instruction.Inthissituation,theinterruptwhichwokeupthedevicewillnot

beimmediatelyserviced,butwillratherbeservicedlaterwhentherelatedinterruptisfinallyenabled

orwhenastacklevelbecomesfree.Theothersituationiswheretherelatedinterruptisenabledand

thestackisnotfull,inwhichcasetheregularinterruptresponsetakesplace.Ifaninterruptrequest

flagissethighbeforeenteringtheSLEEPorIDLEMode,thewake-upfunctionoftherelated

interruptwillbedisabled.

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