User’s Manual U18172EJ2V0UD
137
CHAPTER 8 WATCHDOG TIMER
8.1 Functions of Watchdog Timer
The watchdog timer is used to detect an inadvertent program loop. If a program loop is detected, an internal reset
signal is generated.
When a reset occurs due to the watchdog timer, bit 4 (WDTRF) of the reset control flag register (RESF) is set to 1.
For details of RESF, see
CHAPTER 12 RESET FUNCTION
.
Table 8-1. Loop Detection Time of Watchdog Timer
Loop Detection Time
During Low-Speed Internal oscillation Clock Operation
During System Clock Operation
2
11
/f
RL
(4.27 ms)
2
13
/f
X
(819.2
µ
s)
2
12
/f
RL
(8.53 ms)
2
14
/f
X
(1.64 ms)
2
13
/f
RL
(17.07 ms)
2
15
/f
X
(3.28 ms)
2
14
/f
RL
(34.13 ms)
2
16
/f
X
(6.55 ms)
2
15
/f
RL
(68.27 ms)
2
17
/f
X
(13.11 ms)
2
16
/f
RL
(136.53 ms)
2
18
/f
X
(26.21 ms)
2
17
/f
RL
(273.07 ms)
2
19
/f
X
(52.43 ms)
2
18
/f
RL
(546.13 ms)
2
20
/f
X
(104.86 ms)
Remarks 1.
f
RL
: Low-speed internal oscillation clock oscillation frequency
2.
f
X
: System clock oscillation frequency
3.
Figures in parentheses apply to operation at f
RL
= 480 kHz (MAX.), f
X
= 10 MHz.
The operation mode of the watchdog timer (WDT) is switched according to the option byte setting of the on-chip
low-speed internal oscillator as shown in Table 8-2.