NEC mPD780208 Subseries, Руководство пользователя

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CHAPTER 8 WATCH TIMER
173
User’s Manual U11302EJ4V0UM
8.4 Watch Timer Operations
8.4.1 Watch timer operation
When the 32.768 kHz subsystem 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.
The watch timer sets the test input flag (WTIF) to 1 at a 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 1 again
after setting TMC22 to 0 (maximum error: 26.2 ms when operated at 5.0 MHz).
8.4.2 Interval timer operation
The watch timer operates as an interval timer that generates interrupt requests repeatedly at an interval of the
preset count value.
The interval time can be selected using bits 4 to 6 (TMC24 to TMC26) of the watch timer mode control register
(TMC2).
Table 8-3. Interval Timer Interval Time
TMC26 TMC25 TMC24 Interval Time
When Operated at When Operated at When Operated at
f
X
= 5.0 MHz f
X
= 4.19 MHz f
XT
= 32.768 kHz
0 0 0 2
4
x 1/f
W
819
µ
s 978
µ
s 488
µ
s
0 0 1 2
5
x 1/f
W
1.64 ms 1.96 ms 977
µ
s
0 1 0 2
6
x 1/f
W
3.28 ms 3.91 ms 1.95 ms
0 1 1 2
7
x 1/f
W
6.55 ms 7.82 ms 3.91 ms
1 0 0 2
8
x 1/f
W
13.1 ms 15.6 ms 7.81 ms
1 0 1 2 9 x 1/f
W
26.2 ms 31.3 ms 15.6 ms
Other than above Setting prohibited
f
X
: Main system clock oscillation frequency
f
XT
: Subsystem clock oscillation frequency
f
W
: Watch timer clock frequency (f
X
/2 8 or f
XT
)