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CHAPTER 9 WATCHDOG TIMER
9.4 Watchdog Timer Operations
9.4.1 Watchdog timer operation
When bit 4 (WDTM4) of the watchdog timer mode register (WDTM) is set to 1, the watchdog timer is operated
to detect any inadvertent program loop.
The watchdog timer count clock (inadvertent program loop detection time interval) can be selected with bits 0 to
2 (TCL20 to TCL22) of the timer clock select register 2 (TCL2).
Watchdog timer starts by setting bit 7 (RUN) of WDTM to 1. After the watchdog timer is started, set RUN to 1
within the set inadvertent program loop detection time interval. The watchdog timer can be cleared and counting is
started by setting RUN to 1. If RUN is not set to 1 and the inadvertent program loop detection time is past, system
reset or a non-maskable interrupt request is generated according to the WDTM bit 3 (WDTM3) value.
The watchdog timer continues operating in the HALT mode but it stops in the STOP mode. Thus, set RUN to 1
before the STOP mode is set, clear the watchdog timer and then execute the STOP instruction.
Cautions 1. The actual inadvertent program loop detection time may be shorter than the set time by a
maximum of 0.5 %.
2. When the subsystem clock is selected for CPU clock, watchdog timer count operation is
stopped.
Table 9-4. Watchdog Timer Inadvertent Program Loop Detection Time
TCL22
TCL21
TCL20
Inadvertent Program
Loop Detection Time
MCS = 1
MCS = 0
0
0
0
2
11
×
1/f
XX
2
11
×
1/f
X
(410
μ
s)
2
12
×
1/f
X
(819
μ
s)
0
0
1
2
12
×
1/f
XX
2
12
×
1/f
X
(819
μ
s)
2
13
×
1/f
X
(1.64 ms)
0
1
0
2
13
×
1/f
XX
2
13
×
1/f
X
(1.64 ms)
2
14
×
1/f
X
(3.28 ms)
0
1
1
2
14
×
1/f
XX
2
14
×
1/f
X
(3.28 ms)
2
15
×
1/f
X
(6.55 ms)
1
0
0
2
15
×
1/f
XX
2
15
×
1/f
X
(6.55 ms)
2
16
×
1/f
X
(13.1 ms)
1
0
1
2
16
×
1/f
XX
2
16
×
1/f
X
(13.1 ms)
2
17
×
1/f
X
(26.2 ms)
1
1
0
2
17
×
1/f
XX
2
17
×
1/f
X
(26.2 ms)
2
18
×
1/f
X
(52.4 ms)
1
1
1
2
19
×
1/f
XX
2
19
×
1/f
X
(104.9 ms)
2
20
×
1/f
X
(209.7 ms)
Remarks 1.
f
XX
: Main system clock frequency (f
X
or f
X
/2)
: Main system clock oscillation frequency
3.
MCS : Oscillation mode selection register (OSMS) bit 0
4.
Figures in parentheses apply to operation with f
X
= 5.0 MHz.
2.
f
X