Chapter 9 Watchdog Timer; Functions Of Watchdog Timer - NEC 78K0S/KB1+ User Manual

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 15 RESET FUNCTION.
During Low-Speed Internal Oscillation Clock
11
2 /f (4.27 ms)
RL
12
2 /f (8.53 ms)
RL
13
2 /f (17.07 ms)
RL
14
2 /f (34.13 ms)
RL
15
2 /f (68.27 ms)
RL
16
2 /f (136.53 ms)
RL
17
2 /f (273.07 ms)
RL
18
2 /f (546.13 ms)
RL
Remarks 1. f : Low-speed internal oscillation clock frequency
RL
2. f : System clock oscillation frequency
X
3. Figures in parentheses apply to operation at f
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 9-2.
148

CHAPTER 9 WATCHDOG TIMER

Table 9-1. Loop Detection Time of Watchdog Timer
Loop Detection Time
Operation
User's Manual U17446EJ3V1UD
During System Clock Operation
μ
13
2 /f (819.2 s)
X
14
2 /f (1.64 ms)
X
15
2 /f (3.28 ms)
X
16
2 /f (6.55 ms)
X
17
2 /f (13.11 ms)
X
18
2 /f (26.21 ms)
X
19
2 /f (52.43 ms)
X
20
2 /f (104.86 ms)
X
= 480 kHz (MAX.), f
RL
= 10 MHz.
X