Holtek HT66F002 - Reset and Initialisation

Rev. 1.71 48 April 11, 2017 Rev. 1.71 49 April 11, 2017
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
Themaximumtime-outperiodiswhenthe2
15
divisionratioisselected.Asanexample,witha32
kHzLIRCoscillatorasitssourceclock,thiswillgiveamaximumwatchdogperiodofaround1
secondforthe2
15
divisionratio,andaminimumtimeoutof7.8msforthe2
8
divisionration.
“CLR WDT”Instruction
11-stage Divider
7-stage Divider
WE4~WE0 bitsWDTC Register
Reset MCU
LIRC
f
LIRC
8-to-1 MUX
CLR
WS2~WS0
(f
LIRC
/2
1
~ f
LIRC
/2
11
)
WDT Time-out
(2
8
/f
LIRC
~ 2
15
/f
LIRC
)
RES pin reset
“HALT”Instruction
Watchdog Timer
Reset and Initialisation
Aresetfunctionisafundamentalpartofanymicrocontrollerensuringthatthedevicescanbeset
tosomepredeterminedconditionirrespectiveofoutsideparameters.Themostimportantreset
conditionisafterpowerisrstappliedtothemicrocontroller.Inthiscase,internalcircuitrywill
ensurethatthemicrocontroller,afterashortdelay,willbeinawelldefinedstateandreadyto
executetherstprograminstruction.Afterthispower-onreset,certainimportantinternalregisters
willbesettodenedstatesbeforetheprogramcommences.OneoftheseregistersistheProgram
Counter,whichwillberesettozeroforcingthemicrocontrollertobeginprogramexecutionfromthe
lowestProgramMemoryaddress.
Inadditiontothepower-onreset,situationsmayarisewhereitisnecessarytoforcefullyapply
aresetconditionwhenthemicrocontrollerisrunning.Oneexampleofthisiswhereafterpower
hasbeenappliedandthemicrocontrollerisalreadyrunning,theRESlineisforcefullypulledlow.
Insuchacase,knownasanormaloperationreset,someofthemicrocontrollerregistersremain
unchangedallowingthemicrocontrollertoproceedwithnormaloperationaftertheresetlineis
allowedtoreturnhigh.
AnothertypeofresetiswhentheWatchdogTimeroverflowsandresetsthemicrocontroller.All
typesofresetoperationsresultindifferentregisterconditionsbeingsetup.Anotherresetexistsinthe
formofaLowVoltageReset,LVR,whereafullresetisimplementedinsituationswherethepower
supplyvoltagefallsbelowacertainthreshold.