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after reset.
Once you have enabled the watchdog timer, your program must trigger the watchdog
timer every time before it times out. After you trigger the watchdog timer, it will be
set to non-zero value to watchdog counter and start to count down again. If your
program fails to trigger the watchdog timer before time-out, it will generate a reset
pulse to reset the system.
The factor of the watchdog timer time-out constant is approximately 1 second. The
period for the watchdog timer time-out is between 1 to FF timer factors.
If you want to reset your system when watchdog times out, the following table listed
the relation of timer factors between time-out periods.
Time Factor
1
2
3
4
5
"
"
"
FF
Watchdog Timer Enabled
To Enabled the watchdog timer, you have to output a byte of timer factor to the
watchdog register whose address is 2Eh and data port is 2fH. The following is an
Assemble program, which demonstrates how to enable the watchdog timer and set
the time-out period at 28 seconds.
;------------------------------------------------------------------------------------------
; Enter the extended function mode, interruptible double-write
;------------------------------------------------------------------------------------------
Mov
dx, 2eh
Mov
al, 87h
Out
dx,al
Out
dx,al
Mov
al,07h
Time-Out Period
(Seconds)
2
3
4
5
"
"
"
FF
; Enter to extended function mode
Time-Out Period
(Minutes)
1 1
2
3
4
5
"
"
"
FF
Korenix | Software Installation
49
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