S1C62740 TECHNICAL HARDWARE
EPSON
I-21
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Resetting Watchdog Timer)
Control of watchdog
timer
Table 4.2.1 lists the watchdog timer's control bits and their ad-
dresses.
Table 4.2.1 Control bits of watchdog timer
*1 Initial value at the time of initial reset
*5 Constantly "0" when being read
*2 Not set in the circuit
*6 Refer to main manual
*3 Undefined
*7 Page switching in I/O memory is not necessary
*4 Reset (0) immediately after being read
The 1/2 Hz and 1/4 Hz data of the watchdog timer can be read
out. These bits are read only, and writing operations are invalid.
At initial reset, the watchdog timer data is initialized to "00B".
WD0, WD1:
Watchdog timer data
(E5HD0, D1)
Address
Comment
Register
D3
D2
D1
D0
Name
Init
1
0
*1
E2H
TMRST
W
0
TMRST
Reset
–
0
–
*2
*5
*7
Unused
Clock timer and watchdog timer reset
WD0
WDRST
0
WD1
WD0
Reset
–
0
Reset
–
WD1
0
WDRST
E5H
*2
*5
Watchdog timer reset
Unused
Watchdog timer data (1/4 Hz)
Watchdog timer data (1/2 Hz)
R
WR
WDRST:
Watchdog timer reset
(E5HD3)
This is the bit for resetting the watchdog timer.
When "1" is written: Watchdog timer is reset
When "0" is written: No operation
Reading: Always "0"
When "1" is written to WDRST, the watchdog timer is reset, and the
operation restarts immediately after this. When "0" is written to
WDRST, no operation results.
This bit is dedicated for writing, and is always "0" for reading.
TMRST:
Clock timer reset
(E2HD0)
This is the bit for resetting the clock timer and the watchdog timer.
When "1" is written: Clock timer and watchdog timer are reset
When "0" is written: No operation
Reading: Always "0"
When "1" is written to TMRST, the clock timer and the watchdog
timer are reset, and the operation restarts immediately after this.
When "0" is written to TMRST, no operation results.
This bit is dedicated for writing, and is always "0" for reading.
Programming note
The watchdog timer must be reset within 3-second cycles. Because
of this, the watchdog timer data (WD0, WD1) cannot be used for
clocking of 3 seconds or more.