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CHAPTER 11 WATCHDOG TIMER
11.4 Operation of Watchdog Timer
11.4.1 Operation as watchdog timer
The watchdog timer detects an inadvertent program loop when bit 4 (WDTM4) of the watchdog timer mode register
(WDTM) is set to 1.
The count clock (inadvertent loop detection time interval) of the watchdog timer can be selected by bits 0 through
2 (TCL20-TCL22) of the timer clock select register 2 (TCL2). By setting bit 7 (RUN) of WDTM to 1, the watchdog
timer is started. Set RUN to 1 within the set inadvertent loop detection time interval after the watchdog timer has
been started. By setting RUN to 1, the watchdog timer can be cleared and started counting. If RUN is not set to
1, and the inadvertent loop detection time is exceeded, the system is reset or a non-maskable interrupt is generated
by the value of bit 3 (WDTM3) of WDTM.
The watchdog timer continues operation in the HALT mode, but stops in the STOP mode. Therefore, set RUN
to 1 before entering the STOP mode to clear the watchdog timer, and then execute the STOP instruction.
Cautions 1. The actual inadvertent loop detection time may be up to 0.5% shorter than the set time.
2. The count operation of the watchdog timer is stopped when the subsystem clock is selected
as the CPU clock.
Table 11-4. Inadvertent Loop Detection Time of Watchdog Timer
TCL22
TCL21
TCL20
Inadvertent Loop Detection Time
At f
X
= 10.0 MHz
0
0
0
2
12
×
1/f
X
409.6
μ
s
0
0
1
2
13
×
1/f
X
819.2
μ
s
0
1
0
2
14
×
1/f
X
1.64 ms
0
1
1
2
15
×
1/f
X
3.28 ms
1
0
0
2
16
×
1/f
X
6.55 ms
1
0
1
2
17
×
1/f
X
13.1 ms
1
1
0
2
18
×
1/f
X
26.2 ms
1
1
1
2
20
×
1/f
X
104.9 ms
Remarks
1.
f
X
2.
TCL20-TCL22: Bits 0 through 2 of timer clock select register 2 (TCL2)
: Main system clock oscillation frequency