CHAPTER 10 INTERVAL TIMER, WATCH TIMER
User’s Manual U16896EJ2V0UD
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10.3 Cautions
(1) Operation as watch timer
Some time is required before the first watch timer interrupt request signal (INTWT) is generated after operation
is enabled (WTM.WTM1 and WTM.WTM0 bits = 11).
Figure 10-4. Example of Generation of Watch Timer Interrupt Request Signal (INTWT)
(When Interrupt Period = 0.5 s)
It takes 0.515625 (max.) seconds for the first INTWT signal to be generated (2
9
×
1/32768 = 0.015625 (max.)
seconds longer). An INTWT signal is then generated every 0.5 seconds.
0.5 s
0.5 s
0.515625 s
WTM0, WTM1
INTWT
(2) When watch timer and interval timer BRG operate simultaneously
When using the subclock as the count clock for the watch timer, the interval time of interval timer BRG can be
set to any value. Changing the interval time does not affect the watch timer (before changing the interval time,
stop operation).
When using the main clock as the count clock for the watch timer, set the interval time of interval timer BRG to
approximately 65.536 kHz. Do not change this value.
(3) When interval timer BRG and interval timer WT operate simultaneously
When using the subclock as the count clock for interval timer WT, the interval times of interval timers BRG and
WT can be set to any values. They can also be changed later (before changing the value, stop operation).
When using the main clock as the count clock for interval timer WT, the interval time of interval timer BRG can
be set to any value, but cannot be changed later (it can be changed only when interval timer WT stops
operation). The interval time of interval timer WT can be set to
×
2
5
to
×
2
12
of the set value of interval timer
BRG. It can also be changed later.
(4) When watch timer and interval timer WT operate simultaneously
The interval time of interval timer WT can be set to a value between 488
μ
s and 62.5 ms. It cannot be
changed later.
Do not stop interval timer WT (clear (0) the WTM.WTM0 bit) while the watch timer is operating. If the WTM0
bit is set (1) after it had been cleared (0), the watch timer will have a discrepancy of up to 0.5 or 0.25 seconds.
(5) When watch timer, interval timer BRG, and interval timer WT operate simultaneously
When using the subclock as the count clock for the watch timer, the interval times of interval timers BRG and
WT can be set to any values. The interval time of interval timer BRG can be changed later (before changing
the value, stop operation).
When using the main clock as the count clock for the watch timer, set the interval time of interval timer BRG to
approximately 65.536 kHz. It cannot be changed later. The interval time of interval timer WT can be set to a
value between 488
μ
s and 62.5 ms. It cannot be changed later.
Do not stop interval timer BRG (clear (0) the PRSM.BGCE bit) or interval timer WT (clear (0) the WTM.WTM0
bit) while the watch timer is operating.
