Programming The Watchdog Timer - Advantech PCM-3345 Manual

E.1

Programming the watchdog timer

The default configuration of the timer is enabled with system reset.
To enable the watchdog timer, you must make 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 port 443 at time intervals 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 port 443.
If CPU processing comes to a standstill because of EMI or a software
problem, your program's signals to I/O port address 443 of the timer
will be interrupted. The timer will then automatically reset the CPU or
invoke an IRQ, and data processing will continue normally.
You must make 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.
The following example shows how you might program the watchdog
timer in BASIC:
6 4 PCM-3345 User's Manual