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Chapter 9 Watchdog Timer
Operation
8
WDTS1 WDTS0 Watchdog time-out period
00 2
16
Xsystemclock
01 2
18
Xsystemclock
10 2
20
Xsystemclock
11 2
22
Xsystemclock
Watchdog Timer Period
The watchdog timer period is decided by the bp2, 1 (WDTS1-0) of the watchdog timer control register
(WDCTR) and the system clock (fs). If the watchdog timer is not cleared till the set period of watchdog
timer, that is regarded as an error and the watchdog interrupt (WDIRQ) of the non-maskable interrupt
(NMI) is generated.
2CTDW1CTDW0CTAW
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000 timilon
001 2
7
Xkcolcmetsys
010 2
9
Xkcolcmetsys
011 2
11
Xkcolcmetsys
100 2
31
Xkcolcmetsys
10 1 2
51
Xkcolcmetsys
110 2
71
Xkcolcmetsys
111 2
91
Xkcolcmetsys
How to Clear Watchdog Timer
The watchdog timer can be cleared by writing to the watchdog timer control register (WDCTR). The
watchdog timer can be cleared regardless of the writing data to the register. The bit-set (BSET) that does
not change the value is recommended.
The watchdog timer period is generally decided from the execution time for main routine of program.
That should be set the longer period than the value of the execution time for main routine divided by
natural number (1, 2, , , ). And insert the instruction of the watchdog timer clear to the main routine as that
value makes the same cycle.
The Lowest Value for Watchdog Timer Clear
The lowest value for watchdog timer clear is decided by the bp5, 4, 3 (WDTC2, WDTC1, WDTC0) of the
watchdog timer control register (WDCTR).
Table 9-3-2 The Lowest Value for Watchdog Timer Clear
System clock is decided by the CPU mode control register (CPUM).
[
Chapter 2 2-5. Clock Switching ]
Table 9-3-1 Watchdog Timer Period