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HT45F39 Datasheet(PDF) 33 Page - Holtek Semiconductor Inc |
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HT45F39 Datasheet(HTML) 33 Page - Holtek Semiconductor Inc |
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33 / 102 page  Rev. 1.10 32 July 01, 2016 Rev. 1.10 33 July 01, 2016 HT45F39/HT45F391 Ultrasonic Distance Measurement 8-bit Flash MCU HT45F39/HT45F391 Ultrasonic Distance Measurement 8-bit Flash MCU Standby Current Considerations AsthemainreasonforenteringtheSLEEPModeistokeepthecurrentconsumptionofthe devicestoaslowavalueaspossible,perhapsonlyintheorderofseveralmicro-amps,thereare otherconsiderationswhichmustalsobetakenintoaccountbythecircuitdesignerifthepower consumptionistobeminimised.SpecialattentionmustbemadetotheI/Opinsonthedevices.All high-impedanceinputpinsmustbeconnectedtoeitherafixedhighorlowlevelasanyfloatinginput pinscouldcreateinternaloscillationsandresultinincreasedcurrentconsumption. Caremustalsobetakenwiththeloads,whichareconnectedtoI/Opins,whicharesetupasoutputs. Theseshouldbeplacedinaconditioninwhichminimumcurrentisdrawnorconnectedonlyto externalcircuitsthatdonotdrawcurrent,suchasotherCMOSinputs.Alsonotethatadditional standbycurrentwillalsoberequirediftheLIRCoscillatorisenabled. Wake-up AfterthesystementerstheSLEEPMode,itcanbewokenupfromoneofvarioussourceslistedas follows: • AnexternalfallingedgeonPortA • Asysteminterrupt • AWDToverflow IfthesystemiswokenupbyaWDToverflow,aWatchdogTimerresetwillbeinitiated.Although bothofthesewake-upmethodswillinitiatearesetoperation,theactualsourceofthewake-upcan bedeterminedbyexaminingtheTOandPDFflags.ThePDFflagisclearedbyasystempower-upor executingtheclearWatchdogTimerinstructionsandissetwhenexecutingthe"HALT"instruction. TheTOflagissetifaWDTtime-outoccurs,andcausesawake-upthatonlyresetstheProgram CounterandStackPointer,theotherflagsremainintheiroriginalstatus. EachpinonPortAcanbesetupusingthePAWKregistertopermitanegativetransitiononthe pintowake-upthesystem.WhenaPortApinwake-upoccurs,theprogramwillresumeexecution attheinstructionfollowingthe"HALT"instruction.Ifthesystemiswokenupbyaninterrupt,then twopossiblesituationsmayoccur.Thefirstiswheretherelatedinterruptisdisabledortheinterrupt isenabledbutthestackisfull,inwhichcasetheprogramwillresumeexecutionattheinstruction followingthe"HALT"instruction.Inthissituation,theinterruptwhichwoke-upthedeviceswillnot beimmediatelyserviced,butwillratherbeservicedlaterwhentherelatedinterruptisfinallyenabled orwhenastacklevelbecomesfree.Theothersituationiswheretherelatedinterruptisenabledandthe stackisnotfull,inwhichcasetheregularinterruptresponsetakesplace.Ifaninterruptrequestflagisset highbeforeenteringtheSLEEPMode,thewake-upfunctionoftherelatedinterruptwillbedisabled. Programming Considerations IfthedevicesarewokenupfromtheSLEEPModetotheNORMALMode,thehighspeedsystem oscillatorneedsanSSTperiod.ThedevicewillexecutefirstinstructionafterTOis"1". |
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