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User’s Manual U12697EJ3V0UM
CHAPTER 11 WATCH TIMER
11.1 Function
The watch timer has the following functions:
•
Watch timer
•
Interval timer
The watch timer and interval timer functions can be used at the same time.
(1) Watch timer
The watch timer generates an interrupt request (INTWT) at time intervals of 2
14
/f
W
or 2
5
/f
W
by using the main
system clock of 4.19 MHz or subsystem clock of 32.768 kHz.
Caution
A time interval of 0.5 second cannot be generated by the 12.5 MHz main system clock. Use
the 32.768 kHz subsystem clock to generate the 0.5-second time interval.
Remark
f
W
: Watch timer clock oscillation frequency (f
XX
/2
7
or f
XT
)
f
XX
: Main system clock oscillation frequency
f
XT
: Subsystem clock oscillation frequency
(2) Interval timer
The watch timer generates an interrupt request (INTTM3) at time intervals specified in advance.
Table 11-1. Interval Time of Interval Timer
Interval Time
f
XX
= 12.5 MHz
f
XX
= 4.19 MHz
f
XT
= 32.768 kHz
2
11
×
1/f
XX
164
µ
s
488
µ
s
488
µ
s
2
12
×
1/f
XX
328
µ
s
977
µ
s
977
µ
s
2
13
×
1/f
XX
655
µ
s
1.95 ms
1.95 ms
2
14
×
1/f
XX
1.31 ms
3.91 ms
3.91 ms
2
15
×
1/f
XX
2.62ms
7.81 ms
7.81 ms
2
16
×
1/f
XX
5.24 ms
15.6 ms
15.6 ms
Remark
f
XX
: Main system clock oscillation frequency
f
XT
: Subsystem clock oscillation frequency
