ICP WAFER-5823, Руководство пользователя

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This will enable and activate the countdown timer which will
eventually time out and reset the CPU to ensure that this reset
condition does not occur, the Watch-Dog Timer must be
periodically refreshed by reading the same I/O port 043/843H
and 443H. 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 443H
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 = 443H
TIMER_START = 443H
TIMER_STOP = 843H
;;INITIAL TIME PERIOD COUNTER
MOV DX, TIME_PORT
MOV AL,8: ;;8 SECONDS
OUT DX,AL