CHAPTER 9 WATCHDOG TIMER
Preliminary User’s Manual U16898EJ1V0UD
143
9.3 Registers Controlling Watchdog Timer
The watchdog timer is controlled by the following two registers.
•
Watchdog timer mode register (WDTM)
•
Watchdog timer enable register (WDTE)
(1) Watchdog timer mode register (WDTM)
This register sets the overflow time and operation clock of the watchdog timer.
This register can be set by an 8-bit memory manipulation instruction and can be read many times, but can be
written only once after reset is released.
Reset input sets this register to 67H.
Figure 9-2. Format of Watchdog Timer Mode Register (WDTM)
0
WDCS0
1
WDCS1
2
WDCS2
3
WDCS3
4
WDCS4
5
1
6
1
7
0
Symbol
WDTM
Address: FF48H After reset: 67H R/W
WDCS4
Note 1
WDCS3
Note 1
Operation
clock
selection
0
0
Low-speed Ring-OSC clock (f
RL
)
0
1
Clock to peripheral hardware (f
XP
)
1
×
Watchdog timer operation stopped
Overflow time setting
WDCS2
Note 2
WDCS1
Note 2
WDCS0
Note 2
During low-speed Ring-OSC
clock operation
During operation of clock to
peripheral hardware
0 0 0
f
RL
/2
11
(8.53 ms)
f
XP
/2
13
(819.2
µ
s)
0 0 1
f
RL
/2
12
(17.07 ms)
f
XP
/2
14
(1.64 ms)
0 1 0
f
RL
/2
13
(34.13 ms)
f
XP
/2
15
(3.28 ms)
0 1 1
f
RL
/2
14
(68.27 ms)
f
XP
/2
16
(6.55 ms)
1 0 0
f
RL
/2
15
(136.53 ms)
f
XP
/2
17
(13.11 ms)
1 0 1
f
RL
/2
16
(273.07 ms)
f
XP
/2
18
(26.21 ms)
1 1 0
f
RL
/2
17
(546.13 ms)
f
XP
/2
19
(52.43 ms)
1 1 1
f
RL
/2
18
(1.09 s)
f
XP
/2
20
(104.86 ms)
Notes 1. If “low-speed Ring-OSC cannot be stopped” is specified by the option byte, this cannot be set.
The low-speed Ring-OSC clock will be selected no matter what value is written.
2. Reset is released at the maximum cycle (WDCS2, 1, 0 = 1, 1, 1).
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