36
Programming Watchdog Timer
Network Application Platforms
Appendix A
Appendix A:
Programming Watchdog
Timer
A watchdog timer is a piece of hardware that can be
used to automatically detect system anomalies and reset
the processor in case there are any problems. Generally
speaking, a watchdog timer is based on a counter that
counts down from an initial value to zero. The software
selects the counter’s initial value and periodically restarts
it. Should the counter reach zero before the software
restarts it, the software is presumed to be malfunctioning
and the processor’s reset signal is asserted. Thus, the
processor will be restarted as if a human operator had
cycled the power.
For sample watchdog code, see
watchdog
folder on the
Driver and Manual CD
To program the watchdog timer, you must write a program
which writes I/ O port address 443 (hex). The output data is
a value of time interval. The value range is from 01 (hex) to
3E (hex), and the related time interval is 1 sec. to 62 sec.
Data Time Interval
01 1 sec.
02 2 sec.
03 3 sec.
04 4 sec.
..
..
..
3E 62 sec.
After data entry, your program must refresh the
watchdog timer by rewriting the I/O port 443 (hex) while
simultaneously setting it. When you want to disable the
watchdog timer, your program should read I/O port 443
(hex).
For sample watchdog code, see
watchdog
folder on the
Driver and Manual CD