CHAPTER 10 WATCHDOG TIMER
Preliminary User’s Manual U16315EJ1V0UD
212
10.3 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 10-2. 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: FF98H After reset: 67H R/W
WDCS4
Note 1
WDCS3
Note 1
Operation clock selection
0
0
Ring-OSC clock (f
R
)
0
1
X1 input clock (f
XP
)
1
×
Watchdog timer operation stopped
Overflow time setting
WDCS2
Note 2
WDCS1
Note 2
WDCS0
Note 2
During Ring-OSC clock
operation
During X1 input clock operation
0
0
0
f
R
/2
11
(8.53 ms)
f
XP
/2
13
(819.2
µ
s)
0
0
1
f
R
/2
12
(17.07 ms)
f
XP
/2
14
(1.64 ms)
0
1
0
f
R
/2
13
(34.13 ms)
f
XP
/2
15
(3.28 ms)
0
1
1
f
R
/2
14
(68.27 ms)
f
XP
/2
16
(6.55 ms)
1
0
0
f
R
/2
15
(136.53 ms)
f
XP
/2
17
(13.11 ms)
1
0
1
f
R
/2
16
(273.07 ms)
f
XP
/2
18
(26.21 ms)
1
1
0
f
R
/2
17
(546.13 ms)
f
XP
/2
19
(52.43 ms)
1
1
1
f
R
/2
18
(1.09 s)
f
XP
/2
20
(104.86 ms)
Notes 1.
If “Ring-OSC cannot be stopped” is specified by a mask option, this cannot be set. The 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).
Cautions 1. If data is written to WDTM, a wait cycle is generated. Do not write data to WDTM
when the CPU is operating on the subsystem clock and the X1 input clock is
stopped. For details, refer to CHAPTER 29 CAUTIONS FOR WAIT.
2. Set bits 7, 6, and 5 to 0, 1, and 1, respectively (when “Ring-OSC cannot be stopped”
is selected by a mask option, other values are ignored).