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HT45F65 Datasheet(PDF) 61 Page - Holtek Semiconductor Inc |
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HT45F65 Datasheet(HTML) 61 Page - Holtek Semiconductor Inc |
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61 / 231 page  Rev. 1.60 60 �ove��e� ��� �01� Rev. 1.60 61 �ove��e� ��� �01� HT45F65/HT45F66/HT45F67 Glucose Meter 8-Bit Flash MCU 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. AnothertypeofresetiswhentheWatchdogTimeroverflowsandresets.Alltypesofresetoperations resultindifferentregisterconditionsbeingsetup.AnotherresetexistsintheformofaLowVoltage Reset,LVR,whereafullreset,similartotheRESresetisimplementedinsituationswherethepower supplyvoltagefallsbelowacertainthreshold. Reset Functions Therearefivewaysinwhicharesetcanoccur,througheventsoccurringbothinternallyand externally: Power-on Reset Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisfirstappliedto themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromthefirst memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown conditions.AlltheI/Oportandportcontrolregisterswillpowerupinahighconditionensuringthat allI/Oportswillbefirstsettoinputs. RE S VD D In te r nal R es et 0. 9 V DD t RS TD + t SST t RS TD + t SST Power-On Reset Timing Chart RES Pin AstheresetpinissharedwithPC.0,theresetfunctionmustbeselectedusingaconfigurationoption. AlthoughthehasaninternalRCresetfunction,iftheVDDpowersupplyrisetimeisnotfastenough ordoesnotstabilisequicklyatpower-on,theinternalresetfunctionmaybeincapableofproviding properresetoperation.ForthisreasonitisrecommendedthatanexternalRCnetworkisconnected totheRESpin,whoseadditionaltimedelaywillensurethattheRESpinremainslowforanextended periodtoallowthepowersupplytostabilise.Duringthistimedelay,normaloperationofthewillbe inhibited.AftertheRESlinereachesacertainvoltagevalue,theresetdelaytimetRSTDisinvokedto provideanextradelaytimeafterwhichthewillbeginnormaloperation.TheabbreviationSSTinthe figuresstandsforSystemStart-upTimer. |
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