NEC PD78055 Benutzerhandbuch
246
CHAPTER 10 WATCH TIMER
10.4 Watch Timer Operations
10.4.1 Watch timer operation
When the 32.768-kHz subsystem clock or 4.19-MHz main system clock is used, the timer operates as a watch
timer with a 0.5-second or 0.25-second interval.
The watch timer sets the test input 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: 26.2 ms when operated at f
XX
= 5.0 MHz).
10.4.2 Interval timer operation
The watch timer operates as interval timer which generates interrupt requests repeatedly at an interval of the preset
count value.
The interval time can be selected with bits 4 to 6 (TMC24 to TMC26) of the watch timer mode control register.
Table 10-3. Interval Timer Interval Time
When operated at
When operated at
When operated at
f
XX
= 5.0 MHz
f
XX
= 4.19 MHz
f
XT
= 32.768 kHz
0
0
0
2
4
×
1/f
W
410
µ
s
488
µ
s
488
µ
s
0
0
1
2
5
×
1/f
W
819
µ
s
977
µ
s
977
µ
s
0
1
0
2
6
×
1/f
W
1.64 ms
1.95 ms
1.95 ms
0
1
1
2
7
×
1/f
W
3.28 ms
3.91 ms
3.91 ms
1
0
0
2
8
×
1/f
W
6.55 ms
7.81 ms
7.81 ms
1
0
1
2
9
×
1/f
W
13.1 ms
15.6 ms
15.6 ms
Other than above
Setting prohibited
Remark
f
XX
:
Main system clock frequency (f
X
or f
X
/2)
f
X
:
Main system clock oscillation frequency
f
XT
:
Subsystem clock oscillation frequency
f
W
:
Watch timer clock frequency (f
XX
/2
7
or f
XT
)
TMC26 TMC25 TMC24
Interval Time