NEC mPD789026 Subseries, User Manual

Page: 115 / 213

User's Manual U11919EJ3V0UM00
115
CHAPTER 8 WATCHDOG TIMER
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
Inadvertent Loop
Detection Time
At f
X
= 5.0 MHz
2
11
×
1/f
X
410
µ
s
2
13
×
1/f
X
1.64 ms
2
15
×
1/f
X
6.55 ms
2
17
×
1/f
X
26.2 ms
f
X
: System clock oscillation frequency
(2) Interval timer
The interval timer generates an interrupt at a given interval set in advance.
Table 8-2. Interval Time
Interval At f
X
= 5.0 MHz
2
11
×
1/f
X
410
µ
s
2
13
×
1/f
X
1.64 ms
2
15
×
1/f
X
6.55 ms
2
17
×
1/f
X
26.2 ms
f
X
: System clock oscillation frequency