NEC uPD78P078 - Manual (Page 269)

269
CHAPTER 11 WATCH TIMER
11.1 Watch Timer Functions
The watch timer has the following functions.
• Watch timer
• Interval timer
The watch timer and the interval timer can be used simultaneously.
(1) Watch timer
When the 32.768-kHz subsystem clock is used, a flag (WTIF) is set at 0.5-second or 0.25-second intervals.
When the 4.19-MHz (standard: 4.194304 MHz) main system clock is used, a flag (WTIF) is set at 0.5-second
or 0.25-second intervals.
Caution 0.5-second intervals cannot be generated with the 5.0-MHz main system clock. You should
switch to the 32.768 kHz subsystem clock to generate 0.5-second intervals.
(2) Interval timer
Interrupt requests (INTTM3) are generated at the preset time interval.
Table 11-1. 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
2 4 x 1/f
W
410
µ
s 488
µ
s 488
µ
s
2 5 x 1/f
W
819
µ
s 977
µ
s 977
µ
s
2 6 x 1/f
W
1.64 ms 1.95 ms 1.95 ms
2 7 x 1/f W 3.28 ms 3.91 ms 3.91 ms
2 8 x 1/f W 6.55 ms 7.81 ms 7.81 ms
2 9 x 1/f W 13.1 ms 15.6 ms 15.6 ms
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 )
Interval Time