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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
out dx, al
jmp short $+2
mov dx, 71h
in al, dx
jmp short $+2
or al, 08h
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