AXIOMTEK IPC974-519-FL, User Manual

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IPC974 Series U
ser’s Manual
Watchdog Timer
83
APPENDIX A
WATCHDOG TIMER
A.1 About Watchdog Timer
Software stability is major issue in most applications. Some embedded systems are not
watched by an operator 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 solutions in this regard.
The watchdog timer is a counter that triggers a system to reset when it counts down to zero
from a preset value. The software starts the 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.
A.2 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 software has no problems, watchdog
timer will never expire because software will always restart the counter before it reaches zero.