Operation; Operation As Watchdog Timer - NEC V850ES/SA2 UPD703201 Manual

9.4

Operation

9.4.1

Operation as watchdog timer

Watchdog timer operation to detect a program loop is selected by setting bit 4 (WDTM4) of the watchdog timer
mode register (WDTM) to 1.
The count clock (program loop detection time interval) of the watchdog timer can be selected with bits WDCS0 to
WDCS2 of the watchdog timer clock selection register (WDCS). The count operation is started by setting bit 7 (RUN)
of the WDTM register to 1. When, after the count operation is started, the RUN bit is again set to 1 within the set
program loop detection time interval, the watchdog timer is cleared and the count operation starts again.
If the program loop detection time is exceeded without the RUN bit being set to 1, a reset (WDTRES) or a non-
maskable interrupt request signal (INTWDT) is generated, depending on the value of bit WDTM3 of the WDTM
register.
The count operation of the watchdog timer stops in the software STOP mode and IDLE mode. Therefore, set the
RUN bit to 1 before the software STOP mode or IDLE mode is entered in order to clear the watchdog timer.
Because the watchdog timer operates in the HALT mode, do not use the watchdog timer when using the HALT
mode.
Caution Once the WDTM4 bit is cleared to 0 (thereby selecting the interval timer mode), the watchdog
timer mode is not entered as long as RESET is not input.
When the subclock is selected for the CPU clock, the count operation of the watchdog timer
stops (the value of the watchdog timer is maintained).
2
2
2
2
2
2
2
2
Remark
278
CHAPTER 9 WATCHDOG TIMER FUNCTIONS
Table 9-2. Program Loop Detection Time of Watchdog Timer
Clock
f = 17 MHz
X
964 µ s
14
/f
X
15
/f 1.928 ms
X
16
/f 3.855 ms
X
17
/f 7.710 ms
X
18
/f 15.42 ms
X
19
/f 30.84 ms
X
20
/f 61.68 ms
X
22
/f 246.7 ms
X
f = f : Watchdog timer clock frequency
XW X
Preliminary User's Manual U15905EJ1V0UD
Program Loop Detection Time
f = 13.5 MHz f
X XX
1.214 ms 2.048 ms
2.427 ms 4.096 ms
4.855 ms 8.192 ms
9.709 ms 16.38 ms
19.42 ms 32.77 ms
33.84 ms 65.54 ms
77.67 ms 131.1 ms
310.7 ms 524.3 ms
= 8 MHz