HT45F56 datasheet(37/90 Pages) HOLTEK

37 / 90 page

Rev. 1.11

April 11, 2017

Rev. 1.11

April 11, 2017

HT45F56

Shock Detector Flash MCU

HT45F56

Shock Detector Flash MCU

Standby Current Considerations

AsthemainreasonforenteringtheSLEEPorIDLEModeistokeepthecurrentconsumptionofthe

devicetoaslowavalueaspossible,perhapsonlyintheorderofseveralmicro-ampsexceptinthe

IDLE1Mode,thereareotherconsiderationswhichmustalsobetakenintoaccountbythecircuit

designerifthepowerconsumptionistobeminimised.SpecialattentionmustbemadetotheI/Opins

onthedevice.Allhigh-impedanceinputpinsmustbeconnectedtoeitherafixedhighorlowlevelas

anyfloatinginputpinscouldcreateinternaloscillationsandresultinincreasedcurrentconsumption.

Thisalsoappliestodeviceswhichhavedifferentpackagetypes,astheremaybeunbonbedpins.

Thesemusteitherbesetupasoutputsorifsetupasinputsmusthavepull-highresistorsconnected.

Caremustalsobetakenwiththeloads,whichareconnectedtoI/Opins,whicharesetupasoutputs.

Theseshouldbeplacedinaconditioninwhichminimumcurrentisdrawnorconnectedonlyto

externalcircuitsthatdonotdrawcurrent,suchasotherCMOSinputs.IntheIDLE1Modethe

systenoscillatorison,iftheperipheralfunctionclocksourceisderivedfromthehighspeedsystem

oscillator,theadditionalstandbycurrentwillalsobeperhapsintheorderofseveralhundredmicro-

amps.

Wake-up

TominimisepowerconsumptionthedevicecanentertheSLEEPoranyIDLEMode,wherethe

CPUwillbeswitchedoff.However,whenthedeviceiswokenupagain,itwilltakeaconsiderable

timefortheoriginalsystemoscillatortorestart,stabliseandallownormaloperationtoresume.

AfterthesystementerstheSLEEPorIDLEMode,itcanbewokenupfromoneofvarioussources

listedasfollows:

• Anexternalreset

• AnexternalfallingedgeonPortA

• Asysteminterrupt

• AWDToverflow

Ifthesystemiswokenupbyanexternalreset,thedevicewillexperienceafullsystemreset.

However,ifthedeviceiswokenupbyaWDToverflow,aWatchdogTimerresetwillbeinitiated.

Althoughbothofthesewake-upmethodswillinitiatearesetoperation,theactualsourceofthe

wake-upcanbedeterminedbyexaminingtheTOandPDFflags.ThePDFflagisclearedbya

systempower-uporexecutingtheclearWatchdogTimerinstructionsandissetwhenexecutingthe

“HALT”instruction.TheTOflagissetifaWDTtime-outoccurs,andcausesawake-upthatonly

resetstheProgramCounterandStackPointer,theotherflagsremainintheiroriginalstatus.

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.

HT45F56 Datasheet(PDF) 37 Page - Holtek Semiconductor Inc

HT45F56 Datasheet(HTML) 37 Page - Holtek Semiconductor Inc

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