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PC/104-Plus – CPU-1461 Module 45
How to turn the Watch Dog OFF
Make a call to INT52h with AH=00Dh. The Watch Dog will be disabled. Then the Watch Dog doesn’t need to
be periodically refreshed anymore.
Assembler code example:
MOV AH,00Dh
INT 052h
Directly accessing Watch Dog I/O mapped registers
This method must be used when the operating system you are using doesn’t allow you to use the System
BIOS calls, or when you need a different timeout than 2 seconds.
The following assembler code examples explain how to handle the Super I/O (SPIO) National PC87364
Watch Dog:
IO_SPIO_WDT_BASE EQU 7030h ; National PC87364 SPIO Watch Dog
Use the following code to Enable Watch Dog :
; Configure Watch Dog Mask Register ...
MOV DX,IO_SPIO_WDT_BASE+00001h ; Mask Register
IN AL,DX
AND AL,11110000b ; No IRQs refresh
OUT DX,AL
; Set Time Unit ...
MOV DX,IO_SPIO_WDT_BASE+002h ; Status Register
IN AL,DX
AND AL,NOT 10000100b ; Clear Time Unit
OUT DX,AL ; Update Register
; Watch Dog in minutes now
IFDEF TIME_IN_SECONDS
; Add this code to set Watch Dog in seconds …
OR AL,10000000b ; Set Seconds 1
st
step
OUT DX,AL ; Update Register
OR AL,00000100b ; Set Seconds 2
nd
step
OUT DX,AL ; Update Register
ENDIF
; Set Timeout ...