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Os motores de busca de Datasheet de Componentes eletrônicos |
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Os motores de busca de Datasheet de Componentes eletrônicos |
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HT68FB240 Folha de dados(PDF) 45 Page - Holtek Semiconductor Inc |
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HT68FB240 Folha de dados(HTML) 45 Page - Holtek Semiconductor Inc |
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45 / 133 page  Rev. 1.00 �� ���i� 1�� �01� Rev. 1.00 �5 ���i� 1�� �01� HT68FB240 USB Low Speed 8-Bit Flash MCU Standby Current Considerations AsthemainreasonforenteringtheSLEEPorIDLEModeistokeepthecurrentconsumptionofthe devicetoaslowavalueaspossible,perhapsonlyintheorderofseveralmicro-ampsexceptinthe IDLE1Mode,thereareotherconsiderationswhichmustalsobetakenintoaccountbythecircuit designerifthepowerconsumptionistobeminimised.SpecialattentionmustbemadetotheI/Opins onthedevice.Allhigh-impedanceinputpinsmustbeconnectedtoeitherafixedhighorlowlevelas anyfloatinginputpinscouldcreateinternaloscillationsandresultinincreasedcurrentconsumption. Thisalsoappliestothedevicewhichhasdifferentpackagetypes,astheremaybeunbonbedpins. Thesemusteitherbesetupasoutputsorifsetupasinputsmusthavepull-highresistorsconnected. Caremustalsobetakenwiththeloads,whichareconnectedtoI/Opins,whicharesetupasoutputs. Theseshouldbeplacedinaconditioninwhichminimumcurrentisdrawnorconnectedonlyto externalcircuitsthatdonotdrawcurrent,suchasotherCMOSinputs.Alsonotethatadditional standbycurrentwillalsoberequirediftheLIRCoscillatorisenabled. IntheIDLE1Modethesystemoscillatorison,ifthesystemoscillatorisfromthehighspeedsystem oscillator,theadditionalstandbycurrentwillalsobeperhapsintheorderofseveralhundredmicro- amps. Wake-up AfterthesystementerstheSLEEPorIDLEMode,itcanbewokenupfromoneofvarioussources listedasfollows: • AnexternalorUSBreset • AnexternalfallingedgeonPorts • Asysteminterrupt • AWDToverflow IfthesystemiswokenupbyanexternalorUSBreset,thedevicewillexperienceafullsystemreset, however,ifthedeviceiswokenupbyaWDToverflow,aWatchdogTimerresetwillbeinitiated. Althoughbothofthesewake-upmethodswillinitiatearesetoperation,theactualsourceofthe wake-upcanbedeterminedbyexaminingtheTOandPDFflags.ThePDFflagisclearedbya systempower-uporexecutingtheclearWatchdogTimerinstructionsandissetwhenexecutingthe "HALT"instruction.TheTOflagissetifaWDTtime-outoccurs,andcausesawake-upthatonly resetstheProgramCounterandStackPointer,theotherflagsremainintheiroriginalstatus. EachpinonPortscanbesetupusingthePAWUandPXWUregisterstopermitanegativetransition onthepintowake-upthesystem.WhenaPortpinwake-upoccurs,theprogramwillresume executionattheinstructionfollowingthe"HALT"instruction.Ifthesystemiswokenupbyan interrupt,thentwopossiblesituationsmayoccur.Thefirstiswheretherelatedinterruptisdisabled ortheinterruptisenabledbutthestackisfull,inwhichcasetheprogramwillresumeexecutionat theinstructionfollowingthe"HALT"instruction.Inthissituation,theinterruptwhichwoke-upthe devicewillnotbeimmediatelyserviced,butwillratherbeservicedlaterwhentherelatedinterruptis finallyenabledorwhenastacklevelbecomesfree.Theothersituationiswheretherelatedinterrupt isenabledandthestackisnotfull,inwhichcasetheregularinterruptresponsetakesplace.Ifan interruptrequestflagissethighbeforeenteringtheSLEEPorIDLEMode,thewake-upfunctionof therelatedinterruptwillbedisabled. |
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