BS85B12-3/BS85C20-3/BS85C20-5
Touch Key Flash MCU with LCD/LED Driver
Watchdog Timer
TheꢀWatchdogꢀTimerꢀisꢀprovidedꢀtoꢀpreventꢀprogramꢀmalfunctionsꢀorꢀsequencesꢀfromꢀjumpingꢀtoꢀ
unknownꢀlocations,ꢀdueꢀtoꢀcertainꢀuncontrollableꢀexternalꢀeventsꢀsuchꢀasꢀelectricalꢀnoise.
Watchdog Timer Clock Source
TheꢀWatchdogꢀTimerꢀclockꢀsourceꢀisꢀprovidedꢀbyꢀtheꢀinternalꢀlowꢀspeedꢀoscillator,ꢀfLIRC.ꢀTheꢀ
WatchdogꢀTimerꢀsourceꢀclockꢀisꢀthenꢀsubdividedꢀbyꢀaꢀratioꢀofꢀ28ꢀtoꢀ215ꢀtoꢀgiveꢀlongerꢀtimeouts,ꢀ
theꢀactualꢀvalueꢀbeingꢀchosenꢀusingꢀtheꢀWS2~WS0ꢀbitsꢀinꢀtheꢀWDTCꢀregister.ꢀTheꢀLIRCꢀinternalꢀ
oscillatorꢀhasꢀanꢀapproximateꢀperiodꢀofꢀ32kHzꢀatꢀaꢀsupplyꢀvoltageꢀofꢀ5V.
However,ꢀitꢀshouldꢀbeꢀnotedꢀthatꢀthisꢀspecifiedꢀinternalꢀclockꢀperiodꢀcanꢀvaryꢀwithꢀVDD,ꢀtemperatureꢀ
andꢀprocessꢀvariations.
Watchdog Timer Control Register
Aꢀsingleꢀregister,ꢀWDTC,ꢀcontrolsꢀtheꢀrequiredꢀtimeoutꢀperiod.
WDTC Register
Bit
Name
R/W
7
FSYSON
R/W
6
5
4
3
D3
R/W
1
2
D2
R/W
0
1
D1
R/W
1
0
D0
R/W
0
WS2
R/W
1
WS1
R/W
1
WS0
R/W
1
POR
0
Bitꢀ7ꢀꢀ
FSYSON:ꢀfSYSꢀcontrolꢀinꢀIDLEꢀModeꢀ
ꢀ 0:ꢀdisableꢀ
ꢀ 1:ꢀenable
Bitꢀ6~4ꢀ
WS2, WS1, WS0ꢀ:ꢀWDTꢀtime-outꢀperiodꢀselectionꢀ
ꢀ 000:ꢀ256/fLIRCꢀ
001:ꢀ512/fLIRCꢀ
ꢀ
010:ꢀ1024/fLIRCꢀ
ꢀ
011:ꢀ2048/fLIRCꢀ
ꢀ
100:ꢀ4096/fLIRCꢀ
ꢀ
101:ꢀ8192/fLIRCꢀ
ꢀ
110:ꢀ16384/fLIRCꢀ
ꢀ
111:ꢀ32768/fLIRC
ꢀ
TheseꢀthreeꢀbitsꢀdetermineꢀtheꢀdivisionꢀratioꢀofꢀtheꢀWatchdogꢀTimerꢀsourceꢀclock,ꢀ
whichꢀinꢀturnꢀdeterminesꢀtheꢀtimeoutꢀperiod.
Bitꢀ3~0ꢀ
Undefinedꢀbitꢀ
Theseꢀbitsꢀcanꢀbeꢀreadꢀorꢀwrittenꢀbyꢀuserꢀsoftwareꢀprogram.
Rev. 1.20
52
�ꢀꢁꢀst 10ꢂ 2012
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
