Appendix Bwatch Dog Timer - AXIOMTEK OPS830 Series User Manual

OPS830 Series User's Manual
APPENDIX B
WATCH DOG TIMER
About Watchdog Timer
Software stability is major issue in most application. Some embedded systems are not
watched by human for 24 hours. It is usually too slow to wait for someone to reboot
when computer hangs. The systems need to be able to reset automatically when things
go wrong. The watchdog timer gives us solution.
The watchdog timer is a counter that triggers a system reset when it counts down to
zero from a preset value. The software starts counter with an initial value and must reset
it periodically. If the counter ever reaches zero which means the software has crashed,
the system will reboot.
How to Use Watchdog Timer
The I/O port base addresses of watchdog timer are 2E (hex) and 2F (hex). The 2E (hex)
and 2F (hex) are address and data port respectively.
Assume that program A is put in a loop that must e xecute at least once every 10ms.
Initialize watchdog timer with a value bigger than 10ms. If the software has no problems;
watchdog timer will never expire because software will always restart the counter before
it reaches zero.
Watch Dog Timer 53