Electronics America Single-Chip Microcontrollers User's Manual

User’s Manual U15331EJ4V1UD 167
CHAPTER 9 WATCHDOG TIMER
9.1 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 a program loop. When a program loop is detected, a non-maskable
interrupt or the RESET signal can be generated.
Table 9-1. Watchdog Timer Program Loop Detection Time
Program Loop Detection Time At fX = 5.0 MHz
2
11
× 1/fX 410 µ s
2
13
× 1/fX 1.64 ms
2
15
× 1/fX 6.55 ms
2
17
× 1/fX 26.2 ms
fX: Main system clock oscillation frequency
(2) Interval timer
The interval timer generates an interrupt at an arbitrary preset interval.
Table 9-2. Interval Time
Interval At fX = 5.0 MHz
2
11
× 1/fX 410 µ s
2
13
× 1/fX 1.64 ms
2
15
× 1/fX 6.55 ms
2
17
× 1/fX 26.2 ms
fX: Main system clock oscillation frequency