CHAPTER 9 WATCHDOG TIMER
Preliminary User’s Manual U16846EJ1V0UD
176
(2) Watchdog timer enable register (WDTE)
Writing ACH to WDTE clears the watchdog timer counter and starts counting again.
This register can be set by an 8-bit memory manipulation instruction.
RESET input sets this register to 9AH.
Figure 9-3. Format of Watchdog Timer Enable Register (WDTE)
0
1
2
3
4
5
6
7
Symbol
WDTE
Address: FF99H After reset: 9AH R/W
Cautions 1. If a value other than ACH is written to WDTE, an internal reset signal is generated. If
the source clock to the watchdog timer is stopped, however, an internal reset signal
is generated when the source clock to the watchdog timer resumes operation.
2. If a 1-bit memory manipulation instruction is executed for WDTE, an internal reset
signal is generated. If the source clock to the watchdog timer is stopped, however,
an internal reset signal is generated when the source clock to the watchdog timer
resumes operation.
3. The value read from WDTE is 9AH (this differs from the written value (ACH)).
The relationship between the watchdog timer operation and the internal reset signal generated by the watchdog
timer is shown below.
Table 9-4. Relationship Between Watchdog Timer Operation and
Internal Reset Signal Generated by Watchdog Timer
“Ring-OSC Can Be Stopped by Software” Is Selected by Option Byte
Watchdog Timer Stopped
Watchdog
Timer
Operation
Internal
Reset Signal
Generation Cause
“Ring-OSC Cannot Be
Stopped by Software” Is
Selected by Option Byte
(Watchdog Timer Is
Always Operating)
Watchdog Timer Is
Operating
WDCS4 Is Set to 1
Source Clock to
Watchdog Timer Is
Stopped
Watchdog timer
overflows
Internal reset signal is
generated.
Internal reset signal is
generated.
−
−
Write to WDTM for the
second time
Internal reset signal is
generated.
Internal reset signal is
generated.
Internal reset signal is
not generated and the
watchdog timer does
not resume operation.
Internal reset signal is
generated when the
source clock to the
watchdog timer
resumes operation.
Write other than “ACH”
to WDTE
Access WDTE by 1-bit
memory manipulation
instruction
Internal reset signal is
generated.
Internal reset signal is
generated.
Internal reset signal is
not generated.
Internal reset signal is
generated when the
source clock to the
watchdog timer
resumes operation.