CHAPTER 8 WATCH TIMER
User’s Manual U15331EJ4V1UD
163
8.3 Control Registers for Watch Timer
The watch timer is controlled by the following registers.
•
Watch timer mode control register (WTM)
•
Watch timer interrupt time selection register (WTIM)
(1) Watch timer mode control register (WTM)
This register is used to control the watch timer count clock, operation enable/disable status, prescaler interval
time, and the 5-bit counter operation.
WTM is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets this register to 00H.
Figure 8-2. Format of Watch Timer Mode Control Register
Symbol
7 6 5 4 3 2
<1>
<0>
Address
After
reset
R/W
WTM WTM7 WTM6 WTM5 WTM4
0
0
WTM1 WTM0 FF4AH 00H R/W
WTM7
Selection of watch timer count clock (f
W
)
0
f
X
/2
7
(39.1 kHz)
1
f
XT
(32.768 kHz) or f
XT
/2 (16.384 kHz)
Note
WTM6
WTM5
WTM4
Selection
of prescaler interval time
0 0 0
2
4
/f
W
0 0 1
2
5
/f
W
0 1 0
2
6
/f
W
0 1 1
2
7
/f
W
1 0 0
2
8
/f
W
1 0 1
2
9
/f
W
Other than above
Setting prohibited
WTM1
Control of 5-bit counter operation
0
Cleared after stopping operation
1
Start
WTM0
Watch timer operation enable/disable
0
Operation stopped (prescaler and timer are both cleared)
1
Operation
enabled
Note
This is the frequency (f
XT
or f
XT
/2) set via the watch timer interrupt time selection register (WTIM).
Remarks 1.
f
W
: Watch timer clock frequency (f
X
/2
7
, f
XT
, or f
XT
/2)
2.
f
X
: Main system clock oscillation frequency
3.
f
XT
: Subsystem clock oscillation frequency
4.
The parenthesized values apply to operation at f
X
= 5.0 MHz or f
XT
= 32.768 kHz.