Chapter 8 Watchdog Timer; Watchdog Timer Functions - NEC mPD789026 Subseries User Manual

8.1 Watchdog Timer Functions

The watchdog timer has the following functions:
• Watchdog timer
• Interval timer
Caution Select the watchdog timer mode or interval timer mode by using the watchdog timer mode
register (WDTM).
(1) Watchdog timer
The watchdog timer is used to detect inadvertent program loops. When an inadvertent loop is detected, a
non-maskable interrupt or the RESET signal can be generated.
Table 8-1. Inadvertent Loop Detection Time of Watchdog Timer
(2) Interval timer
The interval timer generates an interrupt at a given interval set in advance.

CHAPTER 8 WATCHDOG TIMER

Inadvertent Loop
Detection Time
× 1/f
11
2
X
× 1/f
13
2
X
× 1/f
15
2
X
× 1/f
17
2
X
f : System clock oscillation frequency
X
Table 8-2. Interval Time
Interval
× 1/f
11
2
X
× 1/f
13
2
X
× 1/f
15
2
X
× 1/f
17
2
X
f : System clock oscillation frequency
X
User's Manual U11919EJ3V0UM00
At f = 5.0 MHz
X
410 µ s
1.64 ms
6.55 ms
26.2 ms
At f = 5.0 MHz
X
410 µ s
1.64 ms
6.55 ms
26.2 ms
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