Holtek HT66F0175 - Pro�Rammin� Considerations; Watchdog Timer; Watchdo� Timer Clock So�Rce; Watchdo� Timer Control Re�Ister

Rev. 1.50 54 August 28, 2017 Rev. 1.50 55 August 28, 2017
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
Programming Considerations
ThehighspeedandlowspeedoscillatorsbothusethesameSSTcounter.Forexample,ifthesystem
iswokenupfromtheSLEEP0ModeandboththeHIRCandLXToscillatorsneedtostart-upfrom
anoffstate.TheLXToscillatorusestheSSTcounteraftertheHIRCoscillatorhasnisheditsSST
period.
• IfthedevicesarewokenupfromtheSLEEP0ModetotheNORMALMode,thehighspeed
systemoscillatorneedsanSSTperiod.ThedeviceswillexecuterstinstructionafterHTOis
“1”.Atthistime,theLXToscillatormaynotbestabilityiff
SUB
isfromLXToscillator.The
samesituationoccursinthepower-onstate.TheLXToscillatorisnotreadyyetwhentherst
instructionisexecuted.
• IfthedevicesarewokenupfromtheSLEEP1ModetoNORMALMode,andthesystemclock
sourceisfromtheHXToscillatorandFSTENis“1”,thesystemclockcanbeswitchedtothe
LIRCoscillatorafterwakeup.
• Thereareperipheralfunctions,suchasWDTandTMs,forwhichthef
SYS
isused.Ifthesystem
clocksourceisswitchedfromf
H
tof
SUB
,theclocksourcetotheperipheralfunctionsmentioned
abovewillchangeaccordingly.
• Theon/offconditionoff
SUB
andf
S
dependsuponwhethertheWDTisenabledordisabledasthe
WDTclocksourceisselectedfromf
SUB
.
Watchdog Timer
TheWatchdogTimerisprovidedtopreventprogrammalfunctionsorsequencesfromjumpingto
unknownlocations,duetocertainuncontrollableexternaleventssuchaselectricalnoise.
Watchdog Timer Clock Source
TheWatchdogTimerclocksourceisprovidedbytheinternalclock,f
SUB
,whichisinturnsupplied
bytheLIRCorLXToscillator.TheLXToscillatorissuppliedbyanexternal32.768kHzcrystal.
TheLIRCinternaloscillatorhasanapproximatefrequencyof32kHzatasupplyvoltageof
5V.However,itshouldbenotedthatthisspecifiedinternalclockfrequencycanvarywithV
DD
,
temperatureandprocessvariations.TheWatchdogTimersourceclockisthensubdividedbyaratio
of2
8
to2
18
togivelongertimeouts,theactualvaluebeingchosenusingtheWS2~WS0bitsinthe
WDTCregister.
Watchdog Timer Control Register
Asingleregister,WDTC,controlstherequiredtimeoutperiodaswellastheenable/disable
operation.ThisregistercontrolstheoveralloperationoftheWatchdogTimer.