68
MOV AL, 55h ; SPIO Configuration Mode Enable Key
OUT DX, AL ; Enter in configuration mode
; Select Logical Device 8 (watch dog) ...
MOV DX, 3F0h ; SPIO Index Port
MOV AL, 07h ; Logical Device selector is the register 7
OUT DX, AL ; Point to Logical Device selector
INC DX ; SPIO Data Port
MOV AL, 08h ; Logical Device number 8
OUT DX, AL ; Select the Logical Device 8
; Select the time base (seconds or minutes) ...
MOV DX, 3F0h ; SPIO Index Port
MOV AL, F1h ; Watchdog timer unit s regi ster (W DT_UNITS)
OUT DX, AL ; Point to register WDT_UNITS
INC DX ; SPIO Data Port
IN AL, DX ; Read WDT_UNITS
OR AL, 01h ; Mask reserved bits and set time in seconds
; AND AL, FEh ; Mask reserved bits and set time in minutes
MOV BL, AL ; Save new WDT_UNITS value
MOV DX, 3F0h ; SPIO Index Port
MOV AL, F1h ; Watchdog timer units register (WDT_UNITS)
OUT DX, AL ; Point to register WDT_UNITS
INC DX ; SPIO Data Port
MOV AL, BL ; WDT_UNITS value
OUT DX, AL ; Write the new WDT_UNITS value
; Select the watchdog timer timeout value ...
MOV DX, 3F0h ; SPIO Index Port
MOV AL, F2h ; Watchdog timeout value (WDT_VAL)
OUT DX, AL ; Point to register WDT_ VAL
INC DX ; SPIO Data Port
MOV AX, 37 ; New WDT_ VAL value (from 0 to 255 - seconds in this
case)
OUT DX, AL ; Write the new WDT_ VAL value
; SPIO: exit from configuration mode ...
MOV DX, 3F0h ; SPIO Index Port
MOV AL, 0AAh ; SPIO Configuration Mode Disable Key
OUT DX, AL ; Exit from configuration mode
• Note: for further information about the watchdog programming, refer to “FDC 37B78x
Advance Information” manual from SMSC.