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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.
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.
WDTS1
0
0
1
1
System clock is decided by the CPU mode control register (CPUM).
[
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
W
D
T
C
2
0
0
0
0
1
1
1
1
Table 9-3-1
WDTS0
0
1
0
1
Chapter 2
2-5. Clock Switching ]
The Lowest Value for Watchdog Timer Clear
W
D
T
C
1
W
A
0
0
1
1
0
0
1
1
Watchdog Timer Period
Watchdog time-out period
16
2
X system clock
18
2
X system clock
20
2
X system clock
2
22
X system clock
W
a
c t
h
d
o
T
C
0
o f
0
1
0
1
0
1
0
1
Chapter 9 Watchdog Timer
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Operation
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IX - 5
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