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HT45R4U датащи(PDF) 67 Page - Holtek Semiconductor Inc |
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HT45R4U датащи(HTML) 67 Page - Holtek Semiconductor Inc |
67 / 105 page Rev. 1.10 66 �a��� 1�� �01� Rev. 1.10 67 �a��� 1�� �01� HT45R4U TinyPowerTM A/D Type e-Banking ASSP OTP MCU with LCD Reset and Initialisation Aresetfunctionisafundamentalpartofanymicrocontrollerensuringthatthedevicecanbeset tosomepredeterminedconditionirrespectiveofoutsideparameters.Themostimportantreset conditionisafterpowerisfirstappliedtothemicrocontroller.Inthiscase,internalcircuitrywill ensurethatthemicrocontroller,afterashortdelay,willbeinawelldefinedstateandreadyto executethefirstprograminstruction.Afterthispower-onreset,certainimportantinternalregisters willbesettodefinedstatesbeforetheprogramcommences.OneoftheseregistersistheProgram Counter,whichwillberesettozeroforcingthemicrocontrollertobeginprogramexecutionfromthe lowestProgramMemoryaddress. Inadditiontothepower-onreset,situationsmayarisewhereitisnecessarytoforcefullyapplya resetconditionwhenthemicrocontrollerisrunning.Oneexampleofthisiswhereafterpowerhas beenappliedandthemicrocontrollerisalreadyrunning,theRESlineisforcefullypulledlow.In suchacase,knownasanormaloperationreset,someoftheregistersremainunchangedallowing themicrocontrollertoproceedwithnormaloperationaftertheresetlineisallowedtoreturnhigh. AnothertypeofresetiswhentheWatchdogTimeroverflowsandresetsthemicrocontroller.All typesofresetoperationsresultindifferentregisterconditionsbeingsetup. AnotherresetexistsintheformofaLowVoltageReset,LVR,whereafullreset,similartotheRES resetisimplementedinsituationswherethepowersupplyvoltagefallsbelowacertainthreshold. Reset Functions Therearefivewaysinwhichamicrocontrollerresetcanoccur,througheventsoccurringbothinternally andexternally: Power-on Reset Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisfirstappliedtothe microcontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromthefirstmemory address,apower-onresetalsoensuresthatcertainotherregistersarepresettoknownconditions.Allthe I/Oportandportcontrolregisterswillpowerupinahighconditionensuringthatallpinswillbefirstset toinputs. AlthoughthemicrocontrollerhasaninternalRCresetfunction,iftheVDDpowersupplyrisetime isnotfastenoughordoesnotstabilisequicklyatpower-on,theinternalresetfunctionmaybe incapableofprovidingproperresetoperation.Forthisreasonitisrecommendedthatanexternal RCnetworkisconnectedtotheRESpin,whoseadditionaltimedelaywillensurethattheRESpin remainslowforanextendedperiodtoallowthepowersupplytostabilise.Duringthistimedelay, normaloperationofthemicrocontrollerwillbeinhibited.AftertheRESlinereachesacertain voltagevalue,theresetdelaytimetRSTDisinvokedtoprovideanextradelaytimeafterwhichthe microcontrollerwillbeginnormaloperation.TheabbreviationSSTinthefiguresstandsforSystem Start-upTimer. RE S VD D SS T Ti me - out Ch ip R es et 0. 9 V DD t RS TD Power-On Reset Timing Chart FormostapplicationsaresistorconnectedbetweenVDDandtheRESpinandacapacitorconnected betweenVSSandtheRESpinwillprovideasuitableexternalresetcircuit.Anywiringconnectedto theRESpinshouldbekeptasshortaspossibletominimiseanystraynoiseinterference. |
Аналогичный номер детали - HT45R4U |
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Аналогичное описание - HT45R4U |
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