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User’s Manual U11302EJ4V0UM
CHAPTER 8 WATCH TIMER
8.1 Watch Timer Functions
The watch timer has the following functions.
•
Watch timer
•
Interval timer
The watch timer and the interval timer can be used simultaneously.
(1) Watch timer
When the 32.768 kHz subsystem clock is used, a flag (WTIF) is set at 0.5-second or 0.25-second intervals.
In addition, when the 4.19 MHz (standard: 4.194304 MHz) main system clock is used, a flag (WTIF) is set
at 0.5-second or 1-second intervals.
Caution
0.5-second intervals cannot be generated with the 5.0 MHz main system clock. Switch
to the 32.768 kHz subsystem clock to generate 0.5-second intervals.
(2) Interval timer
Interrupt requests (INTTM3) are generated at the preset time interval.
Table 8-1. Interval Timer Interval Time
Interval Time
When Operated
When Operated at
When Operated at
at f
X
= 5.0 MHz
f
X
= 4.19 MHz
f
XT
= 32.768 kHz
2
12
x 1/f
X
819
µ
s
978
µ
s
488
µ
s
2
13
x 1/f
X
1.64 ms
1.96 ms
977
µ
s
2
14
x 1/f
X
3.28 ms
3.91 ms
1.95 ms
2
15
x 1/f
X
6.55 ms
7.82 ms
3.91 ms
2
16
x 1/f
X
13.1 ms
15.6 ms
7.81 ms
2
17
x 1/f
X
26.2 ms
31.3 ms
15.6 ms
f
X
:
Main system clock oscillation frequency
f
XT
: Subsystem clock oscillation frequency