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CHAPTER 11 WATCH TIMER
11.1 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 4.19-MHz (standard: 4.194304 MHz) main system clock is used, a flag (WTIF) is set at 0.5-second
or 0.25-second intervals.
Caution 0.5-second intervals cannot be generated with the 5.0-MHz main system clock. You should
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 11-1. Interval Timer Interval Time
When operated at When operated at When operated at
f
XX = 5.0 MHz fXX = 4.19 MHz fXT = 32.768 kHz
2
4
x 1/fW 410
µ
s 488
µ
s 488
µ
s
2
5
x 1/fW 819
µ
s 977
µ
s 977
µ
s
2
6
x 1/fW 1.64 ms 1.95 ms 1.95 ms
2
7
x 1/fW 3.28 ms 3.91 ms 3.91 ms
2
8
x 1/fW 6.55 ms 7.81 ms 7.81 ms
2
9
x 1/fW 13.1 ms 15.6 ms 15.6 ms
f
XX : Main system clock frequency (fX or fX/2)
fX : Main system clock oscillation frequency
fXT : Subsystem clock oscillation frequency
f
W : Watch timer clock frequency (fXX/2
7
or fXT)
Interval Time