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Preliminary User’s Manual U16846EJ1V0UD
CHAPTER 9 WATCHDOG TIMER
9.1 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 16 RESET FUNCTION.
Table 9-1. Loop Detection Time of Watchdog Timer
Loop Detection Time
During Ring-OSC Clock Operation
During High-Speed System Clock Operation
f
R
/2
11
(8.53 ms)
f
XP
/2
13
(819.2
µ
s)
f
R
/2
12
(17.07 ms)
f
XP
/2
14
(1.64 ms)
f
R
/2
13
(34.13 ms)
f
XP
/2
15
(3.28 ms)
f
R
/2
14
(68.27 ms)
f
XP
/2
16
(6.55 ms)
f
R
/2
15
(136.53 ms)
f
XP
/2
17
(13.11 ms)
f
R
/2
16
(273.07 ms)
f
XP
/2
18
(26.21 ms)
f
R
/2
17
(546.13 ms)
f
XP
/2
19
(52.43 ms)
f
R
/2
18
(1.09 s)
f
XP
/2
20
(104.86 ms)
Remarks 1. f
R
: Ring-OSC clock oscillation frequency
2. f
XP
: High-speed system clock oscillation frequency
3. Figures in parentheses apply to operation at f
R
= 240 kHz (TYP.), f
XP
= 10 MHz
The operation mode of the watchdog timer (WDT) is switched according to the option byte setting of the on-chip
Ring-OSC as shown in Table 9-2.