MB95630H Series
112
FUJITSU SEMICONDUCTOR LIMITED
MN702-00009-2v0-E
CHAPTER 9 WATCH PRESCALER
9.1 Overview
9.1
Overview
The watch prescaler is a 16-bit down-counting, free-run counter, which is
synchronized with the subclock divided by two or the sub-CR clock divided by
two. It has an interval timer function that continuously generates interrupt
requests at regular intervals.
■
Interval Timer Function
The interval timer function continuously generates interrupt requests at regular intervals, using
the subclock divided by two or the sub-CR clock divided by two as its count clock.
•
The counter of the watch prescaler counts down and an interrupt request is generated
whenever the selected interval time has elapsed.
•
The interval time can be selected from the following eight types:
Table 9.1-1 shows the interval times of the watch prescaler.
*1: 2/F
CRL
=20 µs when F
CRL
=100 kHz
*2: 2/F
CL
=61.035 µs when F
CL
=32.768 kHz
Note:
Refer to the device data sheet for the accuracy of the sub-CR clock frequency.
Table 9.1-1
Interval Times of Watch Prescaler
Interval time
(Sub-CR clock)
(2
n
×
2/F
CRL
*
1
)
Interval time
(Subclock)
(2
n
×
2/F
CL
*
2
)
n=10
20.48 ms
62.5 ms
n=11
40.96 ms
125 ms
n=12
81.92 ms
250 ms
n=13
163.84 ms
500 ms
n=14
327.68 ms
1 s
n=15
655.36 ms
2 s
n=16
1.311 s
4 s
n=17
2.621 s
8 s
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