NEC uPD78P078 Manuale Utente
275
CHAPTER 12 WATCHDOG TIMER
12.1 Watchdog Timer Functions
The watchdog timer has the following functions.
• Watchdog timer
• Interval timer
Caution Select the watchdog timer mode or the interval timer mode with the watchdog timer mode
register (WDTM) (the watchdog timer and the interval timer cannot be used simultaneously).
(1) Watchdog timer mode
An inadvertent program loop (runaway) is detected. Upon detection of the runaway, a non-maskable
interrupt request or RESET can be generated.
Table 12-1. Watchdog Timer Runaway Times
Runaway Detection Time
MCS = 1
MCS = 0
2
11
x 1/f
XX
2
11
x 1/f
X
(410
µ
s)
2
12
x 1/f
X
(819
µ
s)
2
12
x 1/f
XX
2
12
x 1/f
X
(819
µ
s)
2
13
x 1/f
X
(1.64 ms)
2
13
x 1/f
XX
2
13
x 1/f
X
(1.64 ms)
2
14
x 1/f
X
(3.28 ms)
2
14
x 1/f
XX
2
14
x 1/f
X
(3.28 ms)
2
15
x 1/f
X
(6.55 ms)
2
15
x 1/f
XX
2
15
x 1/f
X
(6.55 ms)
2
16
x 1/f
X
(13.1 ms)
2
16
x 1/f
XX
2
16
x 1/f
X
(13.1 ms)
2
17
x 1/f
X
(26.2 ms)
2
17
x 1/f
XX
2
17
x 1/f
X
(26.2 ms)
2
18
x 1/f
X
(52.4 ms)
2
19
x 1/f
XX
2
19
x 1/f
X
(104.9 ms)
2
20
x 1/f
X
(209.7 ms)
Remarks 1. f
XX
: Main system clock frequency (f
X
or f
X
/2)
2. f
X
: Main system clock oscillation frequency
3. MCS : Bit 0 of oscillation mode selection register (OSMS)
4. Figures in parentheses apply to operation with f
X
= 5.0 MHz.