5. Each Component Function
User’s Manual
73
How to Use the Watchdog Timer
YES
*WDT: Watch Dog Timer
Read port 4002h, stop the WDT, and turn off alarm output.
Output set data to port 4003h.
Output of A5h to port 4002h starts the WDT and output
of A5h to the same port clears the timer.
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...
Output data to ports 4001h and 4004h to set the
output mode of event, external alarm.
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NO
BIOS setting
Power ON
Instruct
WDT to stop
Set timer value
Start & clear WDT
Modify timer
value?
Set event
output control
Application
...
To modify the timer value during operation, the WDT
needs to be stopped temporarily.
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Figure 5.4. How to Use the Watchdog Timer
Example use
:
To assign IRQ5 to the event whose time-up value is 15sec:
Out 4004h 02h
: Set the event at the time of WDT expiration to IRQ5.
In 4002h
: Stop the WDT timer and cancel the alarm.
Out 4003h 0Fh
: Set the WDT expiration time to 15sec.
Out 4002h A5h
: Start the WDT.
In 4002h
: Stop the WDT and cancel the alarm.
