Advantech PCM-5825, User Manual

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106 PCM-5825 User's Manual
D.1 Programming the watchdog timer
Jumper J3 controls the watchdog settings. The default configura-
tion of the timer is enabled via a system reset.
To enable the watchdog timer, you must write a program which
writes 1 to I/O port address 443 (hex) at regular intervals. The first
time your program reads the port, it enables the watchdog timer.
After that, your program must write 1 to the port at time interval of
less than 1.6 seconds, otherwise the watchdog timer will activate
and reset the CPU or generate an interrupt on IRQ11. When you
want to disable the watchdog timer, your program should write 0
to I/O port 443.
If CPU processing comes to a standstill because of EMI or a
software bug, your program's signals to I/O port 443 to the timer
will be interrupted. The timer will then automatically reset the
CPU or invoke an IRQ, and data processing will continue normal-
ly.
You must write your program so that it writes 1 to I/O port 443 at
an interval shorter than the timer's preset interval. The timer's
intervals have a tolerance of ± 30%, so you should program an
instruction that will refresh the timer about every second.