CHAPTER 8 WATCH TIMER
User’s Manual U15075EJ2V1UD
179
8.3 Watch Timer Control Register
The watch timer is controlled by the watch timer mode control register (WTM).
• Watch timer mode control register (WTM)
WTM selects a count clock for the watch timer and specifies whether to enable operation of the timer. It also
specifies the prescaler interval and how the 5-bit counter is controlled.
WTM is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets WTM to 00H.
Figure 8-2. Format of Watch Timer Mode Control Register
Watch timer count clock selection
WTM7
Prescaler interval selection
WTM6
0
0
0
0
1
1
2
4
/f
W
(488 s)
2
5
/f
W
(977 s)
2
6
/f
W
(1.95 ms)
2
7
/f
W
(3.91 ms)
2
8
/f
W
(7.81 ms)
2
9
/f
W
(15.6 ms)
WTM5
0
0
1
1
0
0
WTM4
0
1
0
1
0
1
Control of 5-bit counter operation
WTM1
0
1
Cleared after stop
Started
Watch timer operation
WTM0
0
1
Operation disabled (both prescaler and timer cleared)
Operation enabled
Other than above
f
X
/2
7
f
XT
(39.1 kHz)
(32.768 kHz)
Setting prohibited
WTM7
WTM6
WTM5
WTM4
0
0
WTM1
WTM0
WTM
7
6
5
4
Symbol
Address
After reset
R/W
FF4AH
00H
R/W
3
2
1
0
0
1
µ
µ
Remarks 1.
f
W
: Watch timer clock frequency (f
X
/2
7
or f
XT
)
2.
f
X
: Main system clock oscillation frequency
3.
f
XT
: Subsystem clock oscillation frequency
4.
The parenthesized values apply to operation at f
W
= 32.768 kHz.