Peak 555A User’s Guide
Watch Dog Timer A-6
e.
Clear WDT (this operation should be repeatedly executed before
WDT time
out, e.g. if WDT time out set at 16 sec., then to clear WDT,
the instruction
should be executed within 16 sec. repeatedly)
MOV
DX, 0F2
IN
AL, DX
f.
Disable WDT
MOV
DX, 70
MOV
AL, 7D
OUT
DX, AL
MOV
DX, 71
IN
AL, DX
AND
AL, 0F7
OUT
DX, AL
MOV
BL, AL
MOV
DX, 70
MOV
AL, 7D
OUT
DX, AL
MOV
DX, 71
MOV
AL, BL
OUT
DX, AL
You can also combine programming procedure b+c+d with same subroutine, for
example, set WDT=1 sec, select NMI and go to enable WDT. The instruction as
followings.
MOV
AL, 01E
; Directly write to port F2 to set WDT=1 sec, select
NMI
and Enable WDT
MOV
DX, 0F2
OUT
DX, AL
MOV
DX, 70
; Save to CMOS index 7D
MOV
AL, 7D
OUT
DX, AL
MOV
AL, 01E
MOV
DX, 71
OUT
DX, AL
