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HT45R4U Folha de dados(PDF) 46 Page - Holtek Semiconductor Inc |
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HT45R4U Folha de dados(HTML) 46 Page - Holtek Semiconductor Inc |
46 / 105 page Rev. 1.10 46 �a��� 1�� �01� Rev. 1.10 47 �a��� 1�� �01� HT45R4U TinyPowerTM A/D Type e-Banking ASSP OTP MCU with LCD Timer/Event Counter Pins Internal Filter TheexternalTimer/EventCounterpinsareconnectedtoaninternalfiltertoreducethepossibility ofunwantedeventcountingeventsorinaccuratepulsewidthmeasurementsduetoadversenoiseor spikesontheexternalTimer/EventCounterinputsignal.Asthisinternalfiltercircuitwillconsume alimitedamountofpower,aconfigurationoptionisprovidedtoswitchoffthefilterfunction,an optionwhichmaybebeneficialinpowersensitiveapplications,butinwhichtheintegrityofthe inputsignalishigh.Caremustbetakenwhenusingthefilteron/offconfigurationoptionasitwill beappliednotonlytobothexternalTimer/EventCounterpinsbutalsototheexternalinterruptinput pins.IndividualTimer/EventCounterorexternalinterruptpinscannotbeselectedtohaveafilteron/ offfunction. Programming Considerations Whenconfiguredtoruninthetimermode,theinternalsystemclockisusedasthetimerclocksource andisthereforesynchronisedwiththeoveralloperationofthemicrocontroller.Inthismodewhenthe appropriatetimerregisterisfull,themicrocontrollerwillgenerateaninternalinterruptsignaldirecting theprogramflowtotherespectiveinternalinterruptvector.Forthepulsewidthmeasurementmode, theinternalsystemclockisalsousedasthetimerclocksourcebutthetimerwillonlyrunwhenthe correctlogicconditionappearsontheexternaltimerinputpin.Asthisisanexternaleventandnot synchronizedwiththeinternaltimerclock,themicrocontrollerwillonlyseethisexternaleventwhen thenexttimerclockpulsearrives.Asaresult,theremaybesmalldifferencesinmeasuredvalues requiringprogrammerstotakethisintoaccountduringprogramming.Thesameappliesifthetimeris configuredtobeintheeventcountingmode,whichagainisanexternaleventandnotsynchronised withtheinternalsystemortimerclock. WhentheTimer/EventCounterisread,orifdataiswrittentothepreloadregister,theclockisinhibited toavoiderrors,howeverasthismayresultinacountingerror,thisshouldbetakenintoaccountbythe programmer.Caremustbetakentoensurethatthetimersareproperlyinitialisedbeforeusingthem forthefirsttime.Theassociatedtimerenablebitsintheinterruptcontrolregistermustbeproperlyset otherwisetheinternalinterruptassociatedwiththetimerwillremaininactive.Theedgeselect,timer modeandclocksourcecontrolbitsintimercontrolregistermustalsobecorrectlysettoensurethe timerisproperlyconfiguredfortherequiredapplication.Itisalsoimportanttoensurethataninitial valueisfirstloadedintothetimerregistersbeforethetimerisswitchedon;thisisbecauseafterpower- ontheinitialvaluesofthetimerregistersareunknown.Afterthetimerhasbeeninitialisedthetimer canbeturnedonandoffbycontrollingtheenablebitinthetimercontrolregister.Notethatsetting thetimerenablebithightoturnthetimeron,shouldonlybeexecutedafterthetimermodebitshave beenproperlysetup.Settingthetimerenablebithightogetherwithamodebitmodification,may leadtoimpropertimeroperationifexecutedasasingletimercontrolregisterbytewriteinstruction. WhentheTimer/Eventcounteroverflows,itscorrespondinginterruptrequestflagintheinterrupt controlregisterwillbeset.Ifthetimerinterruptisenabledthiswillinturngenerateaninterrupt signal.Howeverirrespectiveofwhethertheinterruptsareenabledornot,aTimer/Eventcounter overflowwillalsogenerateawake-upsignalifthedeviceisinaPower-downcondition.This situationmayoccuriftheTimer/EventCounterisintheEventCountingModeandiftheexternal signalcontinuestochangestate.Insuchacase,theTimer/EventCounterwillcontinuetocount theseexternaleventsandifanoverflowoccursthedevicewillbewokenupfromitsPower-down condition.Topreventsuchawake-upfromoccurring,thetimerinterruptrequestflagshouldfirstbe sethighbeforeissuingtheHALTinstructiontoenterthePowerDownMode. |
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