Epson S1C63558 - Manual (Page 34)

24 EPSON S1C63558 TECHNICAL MANUAL
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Watchdog Timer)
4.2.3 I/O memory of watchdog timer
Table 4.2.3.1 shows the I/O address and control bits for the watchdog timer.
Table 4.2.3.1 Control bits of watchdog timer
Address Comment
D3 D2
Register
D1 D0 Name Init
∗
1 1 0
FF07H
0 0 WDEN WDRST
R/W W R
0 ∗ 3
0
∗ 3
WDEN
WDRST
∗ 3
– ∗ 2
–
∗ 2
1
Reset
Enable
Reset
Disable
Invalid
Unused
Unused
Watchdog timer enable
Watchdog timer reset (writing)
*1 Initial value at initial reset
*2 Not set in the circuit
*3 Constantly "0" when being read
WDEN: Watchdog timer enable register (FF07H•D1)
Selects whether the watchdog timer is used (enabled) or not (disabled).
When "1" is written: Enabled
When "0" is written: Disabled
Reading: Valid
When "1" is written to the WDEN register, the watchdog timer starts count operation. When "0" is written,
the watchdog timer does not count and does not generate the interrupt (NMI).
At initial reset, this register is set to "1".
WDRST: Watchdog timer reset (FF07H•D0)
Resets 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 restarts immediately after that. When "0"
is written, no operation results.
This bit is dedicated for writing, and is always "0" for reading.
4.2.4 Programming notes
(1) When the watchdog timer is being used, the software must reset it within 3-second cycles.
(2) Because the watchdog timer is set in operation state by initial reset, set the watchdog timer to disabled
state (not used) before generating an interrupt (NMI) if it is not used.