AXIOMTEK tBOX311-820-FL Series, User Manual

Page: 75 / 88

tBOX311-820-FL Series User
’
s Manual
Watchdog Timer
67
APPENDIX A
WATCHDOG TIMER
About Watchdog Timer
Software stability is major issue in most applications. 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. It can be set by programming
its 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 the Watchdog Timer
A
ssembler Sample Code
;Enable WDT:
mov dx,2Eh
mov al,87h ;Un-lock super I/O
out dx,al
out dx,al
;Select Logic device:
mov dx,2Eh
mov al,07h
out dx,al
mov dx,2Fh
mov al,08h
out dx,al