CHAPTER 8 WATCH TIMER
(1) Watch timer
The 4.19 MHz main system clock or 32.768 kHz subsystem clock is used to issue an interrupt request
(INTWT) at 0.5-second intervals.
Caution When the main system clock is operating at 5.0 MHz, it cannot be used to generate a 0.5-
second interval. In this case, the subsystem clock, which operates at 32.768 kHz, should
be used instead.
(2) Interval timer
The interval timer is used to generate an interrupt request (INTWTI) at specified intervals.
Table 8-1. Interval Generated Using the Interval Timer
Interval
24 × 1/fW
At fX = 5.0 MHz
409.6 µs
At fX = 4.19 MHz
489 µs
At fXT = 32.768 kHz
488 µs
25 × 1/fW
26 × 1/fW
27 × 1/fW
28 × 1/fW
29 × 1/fW
819.2 µs
1.64 ms
3.28 ms
6.55 ms
13.1 ms
978 µs
977 µs
1.96 ms
3.91 ms
7.82 ms
15.6 ms
1.95 ms
3.91 ms
7.81 ms
15.6 ms
Remarks 1. fW: Watch timer clock frequency (fX/27 or fXT)
2. fX: Main system clock oscillation frequency
3. fXT: Subsystem clock oscillation frequency
8.2 Watch Timer Configuration
The watch timer includes the following hardware.
Table 8-2. Watch Timer Configuration
Configuration
Item
Counter
5 bits × 1
Prescaler
9 bits × 1
Control register
Watch timer mode control register (WTM)
User’s Manual U15075EJ1V0UM00
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NEC [ NEC ]
