Chapter 11 Watchdog Timer; Functions Of Watchdog Timer - NEC 78K0 User Manual

11.1 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 22 RESET FUNCTION.
During Ring-OSC Clock Operation
11
f /2
R
12
f /2
R
13
f /2
R
14
f /2
R
15
f /2
R
16
f /2
R
17
f /2
R
18
f /2
R
Remarks 1. f
The operation mode of the watchdog timer (WDT) is switched according to the mask option setting of the on-chip
Ring-OSC as shown in Table 11-2.
262

CHAPTER 11 WATCHDOG TIMER

Table 11-1. Loop Detection Time of Watchdog Timer
Loop Detection Time
(8.53 ms)
(17.07 ms)
(34.13 ms)
(68.27 ms)
(136.53 ms)
(273.07 ms)
(546.13 ms)
(1.09 s)
: Ring-OSC clock oscillation frequency
R
2. f : X1 input clock oscillation frequency
XP
3. Figures in parentheses apply to operation at f
User's Manual U15947EJ2V0UD
During X1 Input Clock Operation
µ
13
f /2 (819.2 s)
XP
14
f /2 (1.64 ms)
XP
15
f /2 (3.28 ms)
XP
16
f /2 (6.55 ms)
XP
17
f /2 (13.11 ms)
XP
18
f /2 (26.21 ms)
XP
19
f /2 (52.43 ms)
XP
20
f /2 (104.86 ms)
XP
*
= 240 kHz (TYP.), f
R
= 10 MHz
XP