CHAPTER 8 WATCH TIMER
8.3 Watch Timer Control Register
The watch timer is controlled by the watch timer mode control register (WTM).
•
Watch timer mode control register (WTM)
WTM selects a count clock for the watch timer and specifies whether to enable operation of the timer. It also
specifies the prescaler interval and how the 5-bit counter is controlled.
WTM is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets WTM to 00H.
Figure 8-2. Format of Watch Timer Mode Control Register
Symbol
WTM
7
6
5
4
3
0
2
0
1
0
Address
FF4AH
After reset
00H
R/W
R/W
WTM7
WTM6
WTM5
WTM4
WTM1
WTM0
WTM7
Watch timer count clock selection
f
f
X
/27
(39.1 kHz)
0
1
(32.768 kHz)
XT
WTM6
WTM5
WTM4
Prescaler interval selection
24/f
25/f
26/f
27/f
28/f
29/f
W
W
W
W
W
W
(488 s)
µ
0
0
0
0
1
1
0
0
1
1
0
0
0
1
0
1
0
1
(977 s)
µ
(1.95 ms)
(3.91 ms)
(7.81 ms)
(15.6 ms)
Other than above
Setting prohibited
WTM1
Control of 5-bit counter operation
0
1
Cleared after stop
Started
WTM0
Watch timer operation
0
1
Operation disabled (both prescaler and timer cleared)
Operation enabled
Remarks 1. fW: Watch timer clock frequency (fX/27 or fXT)
2. fX: Main system clock oscillation frequency
3. fXT: Subsystem clock oscillation frequency
4. The parenthesized values apply to operation at fW = 32.768 kHz.
User’s Manual U15075EJ1V0UM00
173
NEC [ NEC ]
