UPD78F0138 NEC, UPD78F0138 Datasheet - Page 234

• Manufacturer Part Number: UPD78F0138
• Description: (UPD78xxxx) 8-Bit Single-Chip Microcontrollers
• Manufacturer: NEC

9.4 Watch Timer Operations
9.4.1 Watch timer operation
subsystem clock.
operation starts. When these bits are set to 0, the 5-bit counter is cleared and the count operation stops.
setting WTM1 to 0. In this case, however, the 11-bit prescaler is not cleared. Therefore, an error up to 2
seconds occurs in the first overflow (INTWT) after zero-second start.
Remark
234
The watch timer generates an interrupt request (INTWT) at a specific time interval by using the X1 input clock or
When bit 0 (WTM0) and bit 1 (WTM1) of the watch timer operation mode register (WTM) are set to 1, the count
When the interval timer is simultaneously operated, zero-second start can be achieved only for the watch timer by
The interrupt request is generated at the following time intervals.
WTM3
0
0
1
1
f
f
f
X
XT
W
: X1 input clock oscillation frequency
: Watch timer clock frequency
: Subsystem clock oscillation frequency
WTM2
0
1
0
1
2
2
2
2
Interrupt Time Selection
14
13
5
4
/f
/f
/f
/f
W
W
W
W
Table 9-4. Watch Timer Interrupt Time
CHAPTER 9 WATCH TIMER
User’s Manual U16228EJ2V0UD
0.5 s
0.25 s
977
488
When Operated at f
µ
µ
s
s
(WTM7 = 1)
XT
= 32.768 kHz
0.210 s
0.105 s
410
205
When Operated at f
µ
µ
s
s
(WTM7 = 0)
X
= 10 MHz
11
× 1/f
W