NEC PD78F9488 - Manual (Page 163)

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.