Interval Timer Operation - NEC 78K0 User Manual

10.4.2 Interval timer operation

The watch timer operates as interval timer which generates interrupt requests (INTWTI) repeatedly at an interval of
the preset count value.
The interval time can be selected with bits 4 to 6 (WTM4 to WTM6) of the watch timer operation mode register
(WTM).
When bit 0 (WTM0) of the WTM is set to 1, the count operation starts. When this bit is cleared to 0, the count
operation stops.
WTM6 WTM5 WTM4
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
Remark f : X1 input clock oscillation frequency
X
f : Subsystem clock oscillation frequency
XT
f : Watch timer clock frequency
W
Figure 10-3. Operation Timing of Watch Timer/Interval Timer
5-bit counter
Count clock
Watch timer
interrupt INTWT
Interval timer
interrupt INTWTI
Remark f : Watch timer clock frequency
W
n: The number of times of interval timer operations
Figures in parentheses are for operation with f
260
CHAPTER 10 WATCH TIMER
Table 10-5. Interval Timer Interval Time
Interval Time
4
2 /f
W
5
2 /f
W
6
2 /f
W
7
2 /f
W
8
2 /f
W
9
2 /f
W
10
2 /f
W
11
2 /f
W
0H
Start
Interrupt time of watch timer (0.5 s)
Interval time
(T)
n × T
User's Manual U15947EJ2V0UD
When Operated at
f = 32.768 kHz (WTM7 = 1)
XT
µ
488 s
µ
977 s
1.95 ms
3.91 ms
7.81 ms
15.6 ms
31.3 ms
62.5 ms
*
Overflow
Interrupt time of watch timer (0.5 s)
T
= 32.768 kHz (WTM7 = 1, WTM3, WTM2 = 0, 0)
W
When Operated at
f = 10 MHz (WTM7 = 0)
X
µ
205 s
µ
410 s
µ
820 s
1.64 ms
3.28 ms
6.55 ms
13.1 ms
26.2 ms
Overflow
n × T