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HT66F019 Datasheet(PDF) 52 Page - Holtek Semiconductor Inc |
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HT66F019 Datasheet(HTML) 52 Page - Holtek Semiconductor Inc |
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52 / 175 page  Rev. 1.00 5� De�e��e� 01� �01� Rev. 1.00 53 De�e��e� 01� �01� HT66F019 A/D Flash MCU with EEPROM HT66F019 A/D Flash MCU with EEPROM Reset and Initialisation Aresetfunctionisafundamentalpartofanymicrocontrollerensuringthatthedevicecanbeset tosomepredeterminedconditionirrespectiveofoutsideparameters.Themostimportantreset conditionisafterpowerisfirstappliedtothemicrocontroller.Inthiscase,internalcircuitrywill ensurethatthemicrocontroller,afterashortdelay,willbeinawell-definedstateandreadyto executethefirstprograminstruction.Afterthispower-onreset,certainimportantinternalregisters willbesettodefinedstatesbeforetheprogramcommences.OneoftheseregistersistheProgram Counter,whichwillberesettozeroforcingthemicrocontrollertobeginprogramexecutionfromthe lowestProgramMemoryaddress. AnothertypeofresetiswhentheWatchdogTimeroverflowsandresetsthemicrocontroller.All typesofresetoperationsresultindifferentregisterconditionsbeingsetup.Anotherresetexistsinthe formofaLowVoltageReset,LVR,whereafullresetisimplementedinsituationswherethepower supplyvoltagefallsbelowacertainthreshold. Reset Functions Thereareseveralwaysinwhichamicrocontrollerresetcanoccur,througheventsoccurring internally. Power-on Reset Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisfirstappliedto themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromthefirst memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown conditions.AlltheI/Oportsandportcontrolregisterswillpowerupinahighconditionensuring thatallI/Oportswillbefirstsettoinputs. VDD Powe�-on Reset SST Ti�e-out tRSTD Power-On Reset Timing Chart Low Voltage Reset – LVR Themicrocontrollercontainsalowvoltageresetcircuitinordertomonitorthesupplyvoltageofthe device.TheLVRfunctionisalwaysenabledwithaspecificLVRvoltageVLVR.Ifthesupplyvoltage ofthedevicedropstowithinarangeof0.9V~VLVRsuchasmightoccurwhenchangingthebattery, theLVRwillautomaticallyresetthedeviceinternallyandtheLVRFbitintheCTRLregisterwill alsobesethigh.ForavalidLVRsignal,alowsupplyvoltage,i.e.,avoltageintherangebetween 0.9V~VLVRmustexistforatimegreaterthanthatspecifiedbytLVRintheLVD/LVRElectrical Characteristics.Ifthelowsupplyvoltagestatedoesnotexceedthisvalue,theLVRwillignorethe lowsupplyvoltageandwillnotperformaresetfunction.TheactualVLVRvaluecanbeselected bytheLVS7~LVS0bitsintheLVRCregister.IftheLVS7~LVS0bitsarechangedtosomecertain valuesbytheenvironmentalnoiseorsoftwaresetting,theLVRwillresetthedeviceafteradelay time,tSRESET.Whenthishappens,theLRFbitintheCTRLregisterwillbesethigh.Afterpoweron theregisterwillhavethevalueof01010101B.NotethattheLVRfunctionwillbeautomatically disabledwhenthedeviceenterstheSLEEPorIDLEmode. LVR Inte�nal Reset tRSTD + tSST Low Voltage Reset Timing Chart |
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