Input from port into AL or AX.
Second operand is a port number. If required to access port number over 255 - DX register should be used.
IN AL, im.byte IN AL, DX IN AX, im.byte IN AX, DX
IN AX, 4 ; get status of traffic lights. IN AL, 7 ; get status of stepper-motor. MOV DX,0A400h ;port number in dx IN AX,DX