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HT66F005 Datasheet(PDF) 44 Page - Holtek Semiconductor Inc |
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HT66F005 Datasheet(HTML) 44 Page - Holtek Semiconductor Inc |
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44 / 109 page  Rev. 1.30 44 ���i� ��� �01� Rev. 1.30 45 ���i� ��� �01� HT66F005/HT66F006 Cost-Effective A/D Flash MCU with EEPROM HT66F005/HT66F006 Cost-Effective A/D Flash MCU with EEPROM Watchdog Timer Operation TheWatchdogTimeroperatesbyprovidingadeviceresetwhenitstimeroverflows.Thismeans thatintheapplicationprogramandduringnormaloperationtheuserhastostrategicallyclearthe WatchdogTimerbeforeitoverflowstopreventtheWatchdogTimerfromexecutingareset.Thisis doneusingtheclearwatchdoginstructions.Iftheprogrammalfunctionsforwhateverreason,jumps toanunknownlocation,orentersanendlessloop,theseclearinstructionswillnotbeexecutedinthe correctmanner,inwhichcasetheWatchdogTimerwilloverflowandresetthedevice.TheWatchdog Timeroption,suchasalwaysenableorsoftwarecontrolisselectedusingconfigurationoption.With regardtotheWatchdogTimerenable/disablefunction,therearealsofivebits,WE4~WE0,inthe WDTCregistertoofferadditionalenable/disableandresetcontroloftheWatchdogTimer. WDT Always Enabled IftheWDTconfigurationoptionhasselectedthattheWDTisalwaysenabled,theWE4~WE0 bitsstillhaveaneffectontheWDTfunction.WhentheWE4~WE0bitvalueisequalto01010B or10101B,theWDTfunctionisenabled.However,iftheWE4~WE0bitsarechangedtoany othervaluesexcept01010Band10101B,whichmaybecausedbyexternalinfluencessuchas environmentalnoise,itwillresetthemicrocontrollerafter2~3LIRCclockcycles. WDT Enable/Disabled using the WDT Control Register IftheWDTconfigurationoptionhasselectedthattheWDTisenabled/disabledusingtheWDT controlregister,theWE4~WE0valuescandeterminewhichmodetheWDToperatesin.TheWDT willbedisabledwhentheWE4~WE0bitsaresettoavalueof10101B.TheWDTfunctionwillbe enablediftheWE4~WE0bitvalueisequalto01010B.IftheWE4~WE0bitsaresettoanyother valuesotherthan01010Band10101B,itwillresetthedeviceafter2~3LIRCclockcycles.After poweronthesebitswillhavethevalueof01010B. WDT Configuration Option WE4 ~ WE0 Bits WDT Function ��ways Enab�ed 01010B o� 10101B Enab�e �ny othe� va�ue Reset MCU Cont�o��ed by WDTC Registe� 10101B Disab�e 01010B Enab�e �ny othe� va�ue Reset MCU Watchdog Timer Enable/Disable Control Undernormalprogramoperation,aWatchdogTimertime-outwillinitialiseadeviceresetandset thestatusbitTO.However,ifthesystemisintheSLEEPorIDLEMode,whenaWatchdogTimer time-outoccurs,theTObitinthestatusregisterwillbesetandonlytheProgramCounterandStack Pointerwillbereset.ThreemethodscanbeadoptedtocleartheWatchdogTimercontents.Thefirst isaWDTreset,whichmeansavalueotherthan01010Bor10101BiswrittenintotheWE4~WE0 bitlocations,thesecondistousetheWatchdogTimersoftwareclearinstructionsandthethirdisvia aHALTinstruction.ThereisonlyonemethodofusingsoftwareinstructiontocleartheWatchdog Timerandthatistousethesingle“CLRWDT”instructiontocleartheWDT. Themaximumtimeoutperiodiswhenthe218divisionratioisselected.Asanexample,withthe 32kHzLIRCoscillatorasitssourceclock,thiswillgiveamaximumwatchdogperiodofaround8 secondsforthe218divisionratio,andaminimumtimeoutof7.8msforthe28divisionration. |
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