HT66F20_13 datasheet(70/298 Pages) HOLTEK

70 / 298 page

Rev. 1.90

�e��a�� 18� �01�

Rev. 1.90

�e��a�� 18� �01�

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60

HT66FU30/HT66FU40/HT66FU50/HT66FU60

Enhanced A/D Flash Type 8-Bit MCU with EEPROM

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60

HT66FU30/HT66FU40/HT66FU50/HT66FU60

Enhanced A/D Flash Type 8-Bit MCU with EEPROM

Watchdog Timer Operation

TheWatchdogTimeroperatesbyprovidingadeviceresetwhenitstimeroverflows.Thismeans

thatintheapplicationprogramandduringnormaloperationtheuserhastostrategicallyclearthe

WatchdogTimerbeforeitoverflowstopreventtheWatchdogTimerfromexecutingareset.Thisis

doneusingtheclearwatchdoginstructions.Iftheprogrammalfunctionsforwhateverreason,jumps

toanunkownlocation,orentersanendlessloop,theseclearinstructionswillnotbeexecutedinthe

correctmanner,inwhichcasetheWatchdogTimerwilloverflowandresetthedevice.Someofthe

WatchdogTimeroptions,suchasenable/disable,clocksourceselectionandclearinstructiontype

areselectedusingconfigurationoptions.Inadditiontoaconfigurationoptiontoenable/disablethe

WatchdogTimer,therearealsofourbits,WDTEN3~WDTEN0,intheWDTCregistertoofferan

additionalenable/disablecontroloftheWatchdogTimer.TodisabletheWatchdogTimer,aswell

astheconfigurationoptionbeingsettodisable,theWDTEN3~WDTEN0bitsmustalsobesetto

aspecificvalueof"1010".AnyothervaluesforthesebitswillkeeptheWatchdogTimerenabled,

irrespectiveoftheconfigurationenable/disablesetting.Afterpoweronthesebitswillhavethevalue

of1010.IftheWatchdogTimerisuseditisrecommendedthattheyaresettoavalueof0101for

maximumnoiseimmunity.NotethatiftheWatchdogTimerhasbeendisabled,thenanyinstruction

relatingtoitsoperationwillresultinnooperation.

WDT Configuration Option

WDTEN3~WDTEN0 Bits

WDT

WDT Ena�le

××××

Ena�le

WDT Disa�le

Except 1010

Ena�le

WDT Disa�le

1010

Disa�le

Watchdog Timer Enable/Disable Control

Undernormalprogramoperation,aWatchdogTimertime-outwillinitialiseadeviceresetandset

thestatusbitTO.However,ifthesystemisintheSLEEPorIDLEMode,whenaWatchdogTimer

time-outoccurs,theTObitinthestatusregisterwillbesetandonlytheProgramCounterandStack

Pointerwillbereset.ThreemethodscanbeadoptedtoclearthecontentsoftheWatchdogTimer.

Thefirstisanexternalhardwarereset,whichmeansalowlevelontheRESpin,thesecondisusing

theWatchdogTimersoftwareclearinstructionsandthethirdisviaaHALTinstruction.

TherearetwomethodsofusingsoftwareinstructionstocleartheWatchdogTimer,oneofwhichmust

bechosenbyconfigurationoption.Thefirstoptionistousethesingle"CLRWDT"instructionwhile

thesecondistousethetwocommands"CLRWDT1"and"CLRWDT2".Forthefirstoption,a

simpleexecutionof"CLRWDT"willcleartheWDTwhileforthesecondoption,both"CLRWDT1"

and"CLRWDT2"mustbothbeexecutedalternatelytosuccessfullycleartheWatchdogTimer.

Notethatforthissecondoption,if"CLRWDT1"isusedtocleartheWatchdogTimer,successive

executionsofthisinstructionwillhavenoeffect,onlytheexecutionofa"CLRWDT2"instruction

willcleartheWatchdogTimer.Similarlyafterthe"CLRWDT2"instructionhasbeenexecuted,only

asuccessive"CLRWDT1"instructioncancleartheWatchdogTimer.

Themaximumtimeoutperiodiswhenthe215divisionratioisselected.Asanexample,witha

32.768kHzLXToscillatorasitssourceclock,thiswillgiveamaximumwatchdogperiodofaround

1secondforthe215divisionratio,andaminimumtimeoutof7.8msforthe28divisionration.Ifthe

fSYS/4clockisusedastheWatchdogTimerclocksource,itshouldbenotedthatwhenthesystem

enterstheSLEEPorIDLE0Mode,thentheinstructionclockisstoppedandtheWatchdogTimer

mayloseitsprotectingpurposes.Forsystemsthatoperateinnoisyenvironments,usingthefSUB

clocksourceisstronglyrecommended.

HT66F20 Datasheet(PDF) 70 Page - Holtek Semiconductor Inc

HT66F20 Datasheet(HTML) 70 Page - Holtek Semiconductor Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL