User’s Guide
Watch Dog Timer
A-1
Appendix A
Watchdog Timer
Watchdog Timer Configuration
The watchdog timer will reset the system automatically if the system
program does not refresh the watchdog timer during the watchdog time out
interval. It is defined at I/O port
0443H
and
043H
to enable/disable the
watchdog time out function.
Regarding to the watchdog function, user must have a program to set the
watchdog time out value, and refresh the watchdog timer cycle. If the system
program goes into a dead loop or goes into an abnormal cycle, the watchdog
timer cannot be refreshed immediately. Meanwhile, the system will be reset
by watchdog timer automatically. The watchdog timer will be refreshed by
“disable watchdog output” then “enable watchdog output”.
The following flowchart shows the normal structure of system program.
Watchdog timer examples:
(1)
Setup watchdog timer time out value
:
mov al,0ah
mov dx,70h
out dx,al
jmp short $+2
mov dx,71h
in al,dx
jmp short $+2
and al,0f0h
add ax,TimeValue
; TimeValue= 00h..0fh, reference as
following watchdog time out table
out dx,al
jmp short $+2
mov al, 0bh
mov dx, 70h
