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CHAPTER 10 WATCH TIMER
228
10.4 Watch Timer Operations
10.4.1 Watch timer operation
When the 32.768 kHz subsystem clock or 8.38 kHz main system clock is used, the timer operates as a watch timer
with a 0.5 second or 0.25 second interval. In addition, when the 4.19 MHz main system clock is used, the timer can
operate as a watch timer with a 0.5 second or 1 second interval.
Caution
When 8.38 MHz or 4.19 MHz frequency is used, the time interval is slightly off.
When f
X
= 8.38 MHz frequency is used,
2
8
×
2
14
=
2
22
= 0.5005136… (second)
f
X
8.38
×
10
6
When f
X
= 4.19 MHz frequency is used,
2
8
×
2
13
=
2
21
= 0.5005136… (second)
f
X
4.19
×
10
6
When f
XT
= 32.768 MHz frequency is used,
1
×
2
14
=
2
14
= 0.50000… (second)
f
XT
32.768
×
10
3
When f
X
= 10.0 MHz frequency is used (not intended),
2
8
×
2
14
=
2
22
= 0.4194304 (second)
f
X
10.0
×
10
6
The watch timer sets the interrupt request flag (WTIF) to 1 at the constant time interval. The standby state (STOP
mode/HALT mode) can be cleared by setting WTIF to 1.
When bit 2 (TMC22) of the watch timer mode control register (TMC2) is set to 0, the 5-bit counter is cleared and
the count operation stops.
For simultaneous operation of the interval timer, zero-second start can be achieved by setting TMC22 to 0
(maximum error: 15.6 ms when operated at f
XT
= 32.768 kHz).
Содержание 78011BGC AB8 Series
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