HT45F2020 datasheet(34/85 Pages) HOLTEK

34 / 85 page

Rev. 1.00

April 11, 2017

Rev. 1.00

April 11, 2017

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

Watchdog Timer Operation

TheWatchdogTimeroperatesbyprovidingadeviceresetwhenitstimeroverflows.Thismeans

thatintheapplicationprogramandduringnormaloperationtheuserhastostrategicallyclearthe

WatchdogTimerbeforeitoverflowstopreventtheWatchdogTimerfromexecutingareset.Thisis

doneusingtheclearwatchdoginstructions.Iftheprogrammalfunctionsforwhateverreason,jumps

toanunknownlocation,orentersanendlessloop,theseclearinstructionswillnotbeexecutedinthe

correctmanner,inwhichcasetheWatchdogTimerwilloverflowandresetthedevice.Withregardto

theWatchdogTimerenable/disablefunction,therearefivebits,WE4~WE0,intheWDTCregister

toofferadditionalenable/disableandresetcontroloftheWatchdogTimer.TheWDTfunction

willbedisabledwhentheWE4~WE0bitsaresettoavalueof10101B.TheWDTfunctionwillbe

enablediftheWE4~WE0bitsvalueisequalto01010B.IftheWE4~WE0bitsaresettoanyother

valuesbytheenvironmentalnoiseorsoftwaresetting,except01010Band10101B,itwillresetthe

deviceafteradelaytime,tSRESET.Afterpoweronthesebitswillhavethevalueof01010B.

WE4~WE0 Bits

WDT Function

10101B

Disable

01010B

Enable

Any other value

Reset MCU

Watchdog Timer Enable/Disable Control

Undernormalprogramoperation,aWatchdogTimertime-outwillinitialiseadeviceresetandset

thestatusbitTO.However,ifthesystemisintheSLEEPorIDLEMode,whenaWatchdogTimer

time-outoccurs,theTObitinthestatusregisterwillbesetandonlytheProgramCounterandStack

Pointerwillbereset.ThreemethodscanbeadoptedtoclearthecontentsoftheWatchdogTimer.

ThefirstisaWDTreset,whichmeansacertainvalueexcept01010Band10101Bwrittenintothe

WE4~WE0bitfiled,thesecondisusingtheWatchdogTimersoftwareclearinstructionandthethird

isviaaHALTinstruction.

ThereisonlyonemethodofusingsoftwareinstructiontocleartheWatchdogTimer.Thatistouse

thesingle“CLRWDT”instructiontocleartheWDT.

Themaximumtimeoutperiodiswhenthe215divisionratioisselected.Asanexample,witha

32kHzLIRCoscillatorasitssourceclock,thiswillgiveamaximumwatchdogperiodofaround1

secondsforthe215divisionratio,andaminimumtimeoutof8msforthe28divisionration.

“

CLR WDT”Instruction

8-stage Divider

WDT Prescaler

WE4~WE0 bits

WDTC

Reset MCU

LIRC

fLIRC

fLIRC/28

8-to- 1 MUX

CLR

WS2~WS0

WDT Time-out

(28/fLIRC ~215/fLIRC)

“

HALT”Instruction

Watchdog Timer

HT45F2020 датащи(PDF) 34 Page - Holtek Semiconductor Inc

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