HT45F39 datasheet(35/102 Pages) HOLTEK

35 / 102 page

Rev. 1.10

July 01, 2016

Rev. 1.10

July 01, 2016

HT45F39/HT45F391

Ultrasonic Distance Measurement 8-bit Flash MCU

HT45F39/HT45F391

Ultrasonic Distance Measurement 8-bit Flash MCU

Bit0

WRF:WDTControlregistersoftwareresetflag

0:Notoccurred

1:Occurred

Thisbitissetto1bytheWDTControlregistersoftwareresetandclearedbythe

applicationprogram.Notethatthisbitcanonlybeclearedto0bytheapplication

program.

Watchdog Timer Operation

TheWatchdogTimerclocksourceisprovidedbytheinternalclock,whichissourcedfromthe

LIRCoscillator.Itisalwaysenable.TheWatchdogTimeroperatesbyprovidingadevicereset

whenitstimeroverflows.Thismeansthatintheapplicationprogramandduringnormaloperation

theuserhastostrategicallycleartheWatchdogTimerbeforeitoverflowstopreventtheWatchdog

Timerfromexecutingareset.Thisisdoneusingtheclearwatchdoginstructions.Iftheprogram

malfunctionsforwhateverreason,jumpstoanunknownlocation,orentersanendlessloop,these

clearinstructionswillnotbeexecutedinthecorrectmanner,inwhichcasetheWatchdogTimerwill

overflowandresetthedevices.WithregardtotheWatchdogTimerenable/disablefunction,thereare

fivebits,WE4~WE0,intheWDTCregistertoofferadditionalenable/disableandresetcontrolof

theWatchdogTimer.

WDT Function Control

WhentheWE4~WE0bitvalueisequalto01010Bor10101B,theWDTfunctionisenabled.

However,iftheWE4~WE0bitsarechangedtoanyothervaluesexcept01010Band10101B,which

maybecausedbyexternalinfluencessuchasenvironmentalnoise,itwillresetthemicrocontroller

after2~3LIRCclockcycles.

WE4 ~ WE0 Bits

WDT Function

01010B or 10101B

Enable

Any other value

Reset MCU

Watchdog Timer Enable/Disable Control

Undernormalprogramoperation,aWatchdogTimertime-outwillinitialiseadeviceresetandset

thestatusbitTO.However,ifthesystemisintheSLEEPMode,whenaWatchdogTimertime-out

occurs,theTObitinthestatusregisterwillbesetandonlytheProgramCounterandStackPointer

willbereset.ThreemethodscanbeadoptedtocleartheWatchdogTimercontents.Thefirstisa

WDTreset,whichmeansavalueotherthan01010Bor10101BiswrittenintotheWE4~WE0bit

locations,thesecondistousetheWatchdogTimersoftwareclearinstructionsandthethirdisvia

aHALTinstruction.ThereisonlyonemethodofusingsoftwareinstructiontocleartheWatchdog

Timerandthatistousethesingle"CLRWDT"instructiontocleartheWDT.

Themaximumtimeoutperiodiswhenthe218divisionratioisselected.Asanexample,witha32

kHzLIRCoscillatorasitssourceclock,thiswillgiveamaximumwatchdogperiodofaround8

secondsforthe218divisionratio,andaminimumtimeoutof7.8msforthe28divisionration.

“

CLR WDT”Instruction

8-stage Divider

WDT Prescaler

WE4~WE0 bits

WDTC Register

Reset MCU

LIRC

fSUB

fSUB/28

8-to-1 MUX

CLR

WS2~WS0

(fSUB/28 ~ fSUB/218)

WDT Time-out

(28/fSUB ~ 218/fSUB)

“

HALT”Instruction

Watchdog Timer

HT45F39 Datasheet(PDF) 35 Page - Holtek Semiconductor Inc

HT45F39 Datasheet(HTML) 35 Page - Holtek Semiconductor Inc

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