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 (fW)
0
fX/27 (39.1 kHz)
1 fXT (32.768 kHz) or fXT/2 (16.384 kHz)Note
WTM6 WTM5 WTM4 Selection of prescaler interval time
0 0 0
24/fW
0 0 1
25/fW
0 1 0
26/fW
0 1 1
27/fW
1 0 0
28/fW
1 0 1
29/fW
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 T his is the frequency (fXT or fXT/2) set via the watch timer interrupt time selection register (WTIM).
Remarks 1. f
W: Watch timer clock frequency (fX/27, fXT, or fXT/2)
2. f
X: Main system clock oscillation frequency
3. f
XT: Subsystem clock oscillation frequency
4. The parenthesized values apply to operation at fX = 5.0 MHz or fXT = 32.768 kHz.