HT67F488 datasheet(49/171 Pages) HOLTEK

49 / 171 page

Rev. 1.60

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HT67F488/HT67F489

TinyPowerTM A/D Flash MCU with LCD & EEPROM

• TheWDTwillbeclearedandresumecountingiftheWDTisenabled.

• TheI/Oportswillmaintaintheirpresentconditions.

• Inthestatusregister,thePowerDownflag,PDF,willbesetandtheWatchdogtime-outflag,TO,

willbecleared.

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.Alsonotethatadditional

standbycurrentwillalsoberequiredifenabledtheLXTorLIRCoscillator.

IntheIDLE1Modethesystemoscillatorison,ifthesystemoscillatorisfromthehighspeedsystem

oscillator,theadditionalstandbycurrentwillalsobeperhapsintheorderofseveralhundredmicro-

amps.

Wake-up

AfterthesystementerstheSLEEPorIDLEMode,itcanbewokenupfromoneofvarioussources

listedasfollows:

• AnexternalfallingedgeonPortA

• Asysteminterrupt

• AWDToverflow

IfthedeviceiswokenupbyaWDToverflow,aWatchdogTimerresetwillbeinitiated.Although

bothofthesewake-upmethodswillinitiatearesetoperation,theactualsourceofthewake-upcan

bedeterminedbyexaminingtheTOandPDFflags.ThePDFflagisclearedbyasystempower-upor

executingtheclearWatchdogTimerinstructionsandissetwhenexecutingthe“HALT”instruction.

TheTOflagissetifaWDTtime-outoccurs,andcausesawake-upthatonlyresetstheProgram

CounterandStackPointer,theotherflagsremainintheiroriginalstatus.

EachpinonPortAcanbesetupusingthePAWUregistertopermitanegativetransitiononthepin

towake-upthesystem.WhenaPortApinwake-upoccurs,theprogramwillresumeexecutionat

theinstructionfollowingthe“HALT”instruction.Ifthesystemiswokenupbyaninterrupt,then

twopossiblesituationsmayoccur.Thefirstiswheretherelatedinterruptisdisabledortheinterrupt

isenabledbutthestackisfull,inwhichcasetheprogramwillresumeexecutionattheinstruction

followingthe“HALT”instruction.Inthissituation,theinterruptwhichwoke-upthedevicewillnot

beimmediatelyserviced,butwillratherbeservicedlaterwhentherelatedinterruptisfinallyenabled

orwhenastacklevelbecomesfree.Theothersituationiswheretherelatedinterruptisenabledand

thestackisnotfull,inwhichcasetheregularinterruptresponsetakesplace.Ifaninterruptrequest

flagissethighbeforeenteringtheSLEEPorIDLEMode,thewake-upfunctionoftherelated

interruptwillbedisabled.

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