HT66F25D datasheet(49/175 Pages) HOLTEK

49 / 175 page

A/D Flash Type 8-bit MCU with EEPROM

HT66F24D/HT66F25D

Rev. 1.10

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Rev. 1.10

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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

standbycurrentwillalsoberequirediftheconfigurationoptionshaveenabledtheLXTortheLIRC

oscillator.

IntheIDLE1Modethesystemoscillatorison,ifthesystemoscillatorisfromthehighspeedsystem

oscillator,theadditionalstandbycurrentwillalsobeperhapsintheorderofseveralhundredmicro-amps.

Wake-up

AfterthesystementerstheSLEEPorIDLEMode,itcanbewokenupfromoneofvarioussources

listedasfollows:

• AnexternalfallingedgeonPortA

• Asysteminterrupt

• AWDToverflow

IfthedeviceiswokenupbyaWDToverflow,aWatchdogTimerresetwillbeinitiated.IfaWDT

time-outoccurs,itwillsetTOflagandcauseawake-upthatonlyresetstheProgramCounterand

StackPointer,theotherflagsremainintheiroriginalstatus.

EachpinonPortAcanbesetupusingthePAWUregistertopermitanegativetransitiononthepin

towake-upthesystem.WhenaPortApinwake-upoccurs,theprogramwillresumeexecutionat

theinstructionfollowingtheHALTinstruction.Ifthesystemiswokenupbyaninterrupt,thentwo

possiblesituationsmayoccur.Thefirstiswheretherelatedinterruptisdisabledortheinterrupt

isenabledbutthestackisfull,inwhichcasetheprogramwillresumeexecutionattheinstruction

followingtheHALTinstruction.Inthissituation,theinterruptwhichwoke-upthedevicewillnotbe

immediatelyserviced,butwillratherbeservicedlaterwhentherelatedinterruptisfinallyenabledor

whenastacklevelbecomesfree.Theothersituationiswheretherelatedinterruptisenabledandthe

stackisnotfull,inwhichcasetheregularinterruptresponsetakesplace.Ifaninterruptrequestflag

issethighbeforeenteringtheSLEEPorIDLEMode,thewake-upfunctionoftherelatedinterrupt

willbedisabled.

Programming Considerations

TheHXTandLXToscillatorsbothusethesameSSTcounter.Forexample,ifthesystemiswoken

upfromtheSLEEP0ModeandboththeHXTandLXToscillatorsneedtostart-upfromanoffstate.

TheLXToscillatorusestheSSTcounterafterHXToscillatorhasfinisheditsSSTperiod.

IfthedeviceiswokenupfromtheSLEEP0ModetotheNORMALMode,thehighspeedsystem

oscillatorneedsanSSTperiod.ThedevicewillexecutefirstinstructionaftertheHTObitissetto1.

Atthistime,theLXToscillatormaynotbestabilityiffSUBisfromLXToscillator.Thesamesituation

occursinthepower-onstate.TheLXToscillatorisnotreadyyetwhenthefirstinstructionisexecuted.

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