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HT45F4M Datasheet(PDF) 42 Page - Holtek Semiconductor Inc |
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HT45F4M Datasheet(HTML) 42 Page - Holtek Semiconductor Inc |
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42 / 138 page  Rev. 1.10 4� �an�a�� 1�� �01� Rev. 1.10 4� �an�a�� 1�� �01� HT45F4M Lithium Battery Backup Power ASSP MCU HT45F4M Lithium Battery Backup Power ASSP MCU CTRL Register Bit 7 6 5 4 3 2 1 0 Name FSYSON — — — — LVRF LRF WRF R/W R/W — — — — R/W R/W R/W POR 0 — — — — x 0 0 Bit 7 FSYSON: fSYS Cont�ol in IDLE Mode Desc�ibe elsewhe�e. Bit 6~� “—”: Unimplemented� �ead as 0 Bit � LVRF: LVR function reset flag Describeelsewhere. Bit1 LRF:LVRControlregistersoftwareresetflag Describeelsewhere. Bit0 WRF:WDTControlregistersoftwareresetflag 0:Notoccur 1:Occurred Thisbitissetto1bytheWDTControlregistersoftwareresetandclearedbytheapplication program.Notethatthisbitcanonlybeclearedto0bytheapplicationprogram. Watchdog Timer Operation TheWatchdogTimeroperatesbyprovidingadeviceresetwhenitstimeroverflows.Thismeans thatintheapplicationprogramandduringnormaloperationtheuserhastostrategicallyclearthe WatchdogTimerbeforeitoverflowstopreventtheWatchdogTimerfromexecutingareset.Thisis doneusingtheclearwatchdoginstructions.Iftheprogrammalfunctionsforwhateverreason,jumps toanunknownlocation,orentersanendlessloop,theclearWDTinstructionwillnotbeexecutedin thecorrectmanner,inwhichcasetheWatchdogTimerwilloverflowandresetthedevice.Thereare fivebits,WE4~WE0,intheWDTCregistertoenabletheWDTfunction.WhentheWE4~WE0bits valueisequalto01010Bor10101B,theWDTfunctionisenabled.However,iftheWE4~WE0bits arechangedtoanyothervaluesexcept01010Band10101B,whichiscausedbytheenvironmental noise,itwillresetthemicrocontrollerafter2~3LIRCclockcycles. WE4 ~ WE0 Bits WDT Function 01010B o� 10101B Enable An� othe� val�e Reset MCU Watchdog Timer Enable/Disable Control Undernormalprogramoperation,aWatchdogTimertime-outwillinitialiseadeviceresetandset thestatusbitTO.However,ifthesystemisintheSLEEPorIDLEMode,whenaWatchdogTimer time-outoccurs,theTObitinthestatusregisterwillbesetandonlytheProgramCounterandStack Pointerwillbereset.ThreemethodscanbeadoptedtoclearthecontentsoftheWatchdogTimer. ThefirstisaWDTreset,whichmeansacertainvalueiswrittenintotheWE4~WE0bitfiledexcept 01010Band10101B,thesecondisusingtheWatchdogTimersoftwareclearinstructionsandthe thirdisviaaHALTinstruction. ThereisonlyonemethodofusingsoftwareinstructiontocleartheWatchdogTimer.Thatistouse thesingle“CLRWDT”instructiontocleartheWDT. Themaximumtime-outperiodiswhenthe218divisionratioisselected.Asanexample,witha32 kHzLIRCoscillatorasitssourceclock,thiswillgiveamaximumwatchdogperiodofaround8 secondsforthe218divisionratio,andaminimumtimeoutof7.8msforthe28divisionration. |
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