NEC mPD780024AS Series, Preliminary User'S Manual

Page: 154 / 311

154
CHAPTER 8 WATCH TIMER
Preliminary User’s Manual U16035EJ1V0UM
8.3 Register to Control Watch Timer
Watch timer operation mode register (WTM) is a register to control watch timer.
• Watch timer operation mode register (WTM)
This register sets the watch timer count clock, enables/disables operation, prescaler interval time, and 5-bit
counter operation control.
WTM is set by an 8-bit memory manipulation instruction.
RESET input sets WTM to 00H.
Figure 8-2. Format of Watch Timer Operation Mode Register (WTM)
Address: FF41H After reset: 00H R/W
Symbol 7 6 5 4 3 2 1 0
WTM WTM7 WTM6 WTM5 WTM4 0 0 WTM1 WTM0
WTM7 Watch timer count clock selection
0 f
X
/2
7
(65.4 kHz)
1 f
XT
(32.768 kHz)
WTM6 WTM5 WTM4 Prescaler interval time selection
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 5-bit counter operation control
0 Clear after operation stop
1 Start
WTM0 Watch timer operation enable
0 Operation stop (clear both prescaler and timer)
1 Operation enable
Caution Do not change the count clock and interval time (by setting bits 4 to 7 (WTM4 to WTM7) of WTM)
during watch timer operation.
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. Figures in parentheses apply to operation with f
X
= 8.38 MHz, f
XT
= 32.768 kHz.