This is the code
The DATA SEGMENT
The DATA ENDS

CONTROL the EQU 8006 h
IOA EQU 8000 h
IOB EQU 8002 h
The IOC EQU 8004 h

CODE SEGMENT
ASSUME CS: CODE, DS: DATA
START:
MOV AX, DATA
MOV DS, AX
MOV DX, CONTROL
MOV AX, 0090 h
The OUT DX, AL
AGAIN:
MOV AX, 0
MOV DX, IOA
IN AL, DX
MOV DX, IOB
The OUT DX, AL
JMP AGAIN
CODE ENDS
END START