Register Controlling Watch Timer - NEC 78K0 Series User Manual

10.3 Register Controlling Watch Timer

The watch timer is controlled by the watch timer operation mode register (WTM).
• 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 a 1-bit or 8-bit memory manipulation instruction.
Reset signal generation sets WTM to 00H.
Figure 10-2. Format of Watch Timer Operation Mode Register (WTM)
Address: FF6FH After reset: 00H
Symbol 7
WTM WTM7
WTM7
0
1
WTM6
0
0
0
0
1
1
1
1
WTM3
0
0
1
1
WTM1
0
1
WTM0
0
1
CHAPTER 10 WATCH TIMER
R/W
6 5
WTM6 WTM5 WTM4
Watch timer count clock selection (f
f = 32.768 kHz f
SUB PRS
−
7
f /2 15.625 kHz
PRS
f 32.768 kHz
SUB
WTM5 WTM4
4
0 0 2 /f
5
0 1 2 /f
6
1 0 2 /f
7
1 1 2 /f
8
0 0 2 /f
9
0 1 2 /f
10
1 0 2 /f
11
1 1 2 /f
WTM2
14
0 2 /f
W
13
1 2 /f
W
5
0 2 /f
W
4
1 2 /f
W
Clear after operation stop
Start
Operation stop (clear both prescaler and 5-bit counter)
Operation enable
Preliminary User's Manual U17260EJ3V1UD
4 3 2
WTM3 WTM2
= 2 MHz f = 5 MHz
PRS
39.062 kHz
−
Prescaler interval time selection
W
W
W
W
W
W
W
W
Selection of watch timer interrupt time
5-bit counter operation control
Watch timer operation enable
<1> <0>
WTM1 WTM0
)
W
f = 10 MHz f = 20 MHz
PRS PRS
78.125 kHz 156.25 kHz
289