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HT45F39 Datasheet(PDF) 36 Page - Holtek Semiconductor Inc |
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HT45F39 Datasheet(HTML) 36 Page - Holtek Semiconductor Inc |
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36 / 102 page  Rev. 1.10 36 July 01, 2016 Rev. 1.10 37 July 01, 2016 HT45F39/HT45F391 Ultrasonic Distance Measurement 8-bit Flash MCU HT45F39/HT45F391 Ultrasonic Distance Measurement 8-bit Flash MCU Reset and Initialisation Aresetfunctionisafundamentalpartofanymicrocontrollerensuringthatthedevicescanbesetto somepredeterminedconditionirrespectiveofoutsideparameters.Ahardwareresetwillofcoursebe automaticallyimplementedafterthedevicesarepowered-on,howeverthereareanumberofother hardwareandsoftwareresetsourcesthatcanbeimplementeddynamicallywhenthedevicesarerunning. Reset Overview Themostimportantresetconditionisafterpowerisfirstappliedtothemicrocontroller.Inthiscase, internalcircuitrywillensurethatthemicrocontroller,afterashortdelay,willbeinawelldefined stateandreadytoexecutethefirstprograminstruction.Afterthispower-onreset,certainimportant internalregisterswillbesettodefinedstatesbeforetheprograminstructionscommenceexecution. OneoftheseregistersistheProgramCounter,whichwillberesettozeroforcingthemicrocontroller tobeginprogramexecutionfromthelowestProgramMemoryaddress. Thedevicesprovideseveralresetsourcestogeneratetheinternalresetsignal,providingextended MCUprotection.Thedifferenttypesofresetsarelistedintheaccompanyingtable. Reset Name Abbreviation Indication Bit Register Notes Power-On Reset POR — — Auto generated at power on Low-Voltage Reset LVR LVRF CTRL Low VDD voltage LVRC Register Setting Sofe Reset — LRF CTRL Write to LVRC register Watchdog Reset WDT TO STATUS WDT time-out WDTC Register Setting Software Reset — WRF CTRL Write to WDTC register Reset Source Summary Inadditiontothepower-onreset,situationsmayarisewhereitisnecessarytoforcefullyapplya resetconditionwhenthemicrocontrollerisrunning.AnothertypeofresetiswhentheWatchdog Timeroverflowsandresetsthemicrocontroller.Alltypesofresetoperationsresultindifferent registerconditionsbeingsetup.AnotherresetexistsintheformofaLowVoltageReset,LVR,where afullreset,similartothepowersupplyvoltagefallsbelowacertainthreshold. Reset Functions Thereareseveralwaysinwhichamicrocontrollerresetcanoccur,througheventsoccurringboth internallyandexternally: Power-on Reset Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisfirstappliedto themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromthefirst memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown conditions.AlltheI/Oportandportcontrolregisterswillpowerupinahighconditionensuringthat allpinswillbefirstsettoinputs. VDD Power-on Reset SST Time-out t RSTD Note:tRSTDispower-ondelay,typicaltime=100ms Power-On Reset Timing Chart |
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