CHAPTER 9 WATCHDOG TIMER
User’s Manual U13850EJ6V0UD
265
9.4 Operation
9.4.1 Operation as watchdog timer
Set bit 4 (WDTM4) of the watchdog timer mode register (WDTM) to 1 to operate as a watchdog timer to detect an
inadvertent program loop.
Setting bit 7 (RUN) of WDTM to 1 starts the count operation. After counting starts, if RUN is set to 1 again within
the set time interval for inadvertent program loop detection, the watchdog timer is cleared and counting starts again.
If RUN is not set to 1 and the inadvertent program loop detection time has elapsed, a non-maskable interrupt
(INTWDT) is generated (no reset functions).
The watchdog timer stops running in the IDLE mode and STOP mode. Consequently, set RUN to 1 and clear the
watchdog timer before entering the IDLE mode or STOP mode. Do not set the watchdog timer when operating the
HALT mode since the watchdog timer running in HALT mode.
Cautions 1. The actual inadvertent program loop detection time may be up to 2
10
/f
XX
seconds less than
the set time.
2.
When the subclock is selected for the CPU clock, the watchdog timer stops (retains)
counting.
Table 9-4. Inadvertent Program Loop Detection Time of Watchdog Timer
Inadvertent Program Loop Detection Time
Clock
f
XX
= 20 MHz
Note
f
XX
= 12.58 MHz
2
14
/f
XX
819.2
µ
s
1.3 ms
2
15
/f
XX
1.6 ms
2.6 ms
2
16
/f
XX
3.3 ms
5.2 ms
2
17
/f
XX
6.6 ms
10.4 ms
2
18
/f
XX
13.1 ms
20.8 ms
2
19
/f
XX
26.2 ms
41.6 ms
2
20
/f
XX
52.4 ms
83.3 ms
2
22
/f
XX
209.7 ms
333.4 ms
Note
Only in the V850/SB1.