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543H. This must be done within the time out period that is selected
by software, please refer to the example program.
A tolerance of at least 5% must be maintained to avoid unknown
routines within the operating system (DOS), such as disk I/O that
can be very time consuming. Therefore if the time out period has
been set to 10 seconds, the I/O port 543H must be read within 7
seconds.
Note: when exiting a program it is necessary to disable the
WatchDog Timer, otherwise the system will reset.
Example assembly program:
TIMER_PORT = 543H
TIMER_START = 543H
TIMER_STOP = 943H
;; INITIAL TIME PERIOD COUNTER
MOV DX, TIME_PORT
OUT AL, 8:8 SECONDS
;; ADD YOUR APPLICATION HERE
MOV DX, TIMER_START
IN AL, DX. ;; START COUNTER
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;; ADD YOUR APPLICATION HERE
W_LOOP:
MOV DX, TIMER_STOP
IN AL, DX
MOV DX, TIMER_START
IN AL, DX. ;; RESTART COUNTER
;; ADD YOUR APPLICATION HERE
CMP EXIT_AP, 0
JNE W_LOOP
MOV DX, TIMER_STOP
IN AL, DX
;; EXIT AP