Operation; Operating As Watchdog Timer - NEC V850/SA1 mPD703015 Preliminary User's Manual

9.4 Operation

9.4.1 Operating as watchdog timer

Set bit 4 (WDTM4) of the watchdog timer mode register (WDTM) to 1 to operate as a watchdog timer to detect
program runaway.
Setting bit 7 (RUN) of WDTM to 1 starts the count. After counting starts, if RUN is set to 1 again within the set
time interval for runaway detection, the watchdog timer is cleared and counting starts again.
If RUN is not set to 1 and the runaway detection time has elapsed, a nonmaskable interrupt (INTWDT) is
generated (no reset functions).
The watchdog timer stops running in the STOP mode and IDLE mode. Consequently, set RUN to 1 and clear the
watchdog timer before entering the STOP mode or IDLE mode. However, in the case of STOP mode, clearing or
holding the watchdog timer differs (CESEL = 0: clear, CESEL = 1: hold) according to the value of CESEL bit of the
power saving control register (PSC). Do not set the watchdog timer when operating the HALT mode since the
watchdog timer running in HALT mode.
Cautions 1. Sometimes, the actual runaway detection time is a maximum of 0.5% less than the set time.
2. When the subclock is selected in a CPU clock, the watchdog timer stops (retains) counting.
Note Parenthesized values apply when fxx = 17 MHz.
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CHAPTER 9 WATCHDOG TIMER
Table 9-4. Runaway Detection Time of Watchdog Timer
Runaway Detection Time
/fxx (964 µ s)
14
2
15
2 /fxx (1.928 ms)
16
2 /fxx (3.855 ms)
17
2 /fxx (7.710 ms)
18
2 /fxx (15.42 ms)
19
2 /fxx (30.84 ms)
20
2 /fxx (61.68 ms)
22
2 /fxx (246.7 ms)
Note