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CHAPTER 10 WATCH TIMER
223
CHAPTER 10 WATCH TIMER
10.1 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.
When the 8.38 MHz main system 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.
When a frequency other than above is used, a flag (WTIF) is not set at 0.5/0.25 or 0.5/1.0 intervals.
Caution When 8.38 MHz or 4.19 MHz frequency is used, a time interval has a little error.
(2) Interval timer
Interrupt requests (INTTM3) are generated at the preset time interval.
Table 10-1. Interval Timer Interval Time
Interval Time
When operated
When operated at
When operated at
When operated at
at f
X
= 10.0 MHz
f
X
= 8.38 MHz
f
X
= 4.19 MHz
f
XT
= 32.768 kHz
2
4
×
1/f
W
409.6
µ
s
489
µ
s
978
µ
s
488
µ
s
2
5
×
1/f
W
819.2
µ
s
978
µ
s
1.96 ms
977
µ
s
2
6
×
1/f
W
1.64 ms
1.96 ms
3.91 ms
1.95 ms
2
7
×
1/f
W
3.28 ms
3.91 ms
7.82 ms
3.91 ms
2
8
×
1/f
W
6.55 ms
7.82 ms
15.6 ms
7.81 ms
2
9
×
1/f
W
13.1 ms
15.6 ms
31.3 ms
15.6 ms
Remarks
f
X
: Main system clock oscillation frequency
f
XT
: Subsystem clock oscillation frequency
f
W
: Watch timer clock frequency (f
X
/2
8
or f
XT
)
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