Control Registers For Watch Timer; Format Of Watch Timer Mode Control Register - NEC PD789488 User Manual

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