AXIOMTEK eBOX550-100-FL Series, User Manual

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eBOX550-100-FL Series U
ser’s Manual
Watchdog Timer
63
APPENDIX A
WATCHDOG 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 slo w 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 execute at least once every 10ms.
Initialize watchdog timer with a value bigger than 10ms. If the soft ware has no problems;
watchdog timer will never expire because software will always restart the counter before
it reaches zero.