Lecture 14Basic I/O Interface

Presented ByDr. Shazzad Hosain

Asst. Prof. EECS, NSU

7-segment LED Display00H – 03H are the I/O ports

7654 32100000 0000 Port A0000 0001 Port B0000 0010 Port C0000 0011 Command Register

5 6 4 2 8 9 0 1MEM

1. For 8 (eight) times1. Send data through port A2. Select a segment through port B

OUT PORT, DATA OUT DX, AL

7-segment LED Display00H – 03H are the I/O ports

7654 32100000 0000 Port A0000 0001 Port B0000 0010 Port C0000 0011 Command Register

5 6 4 2 8 9 0 1MEM

MOV BX, 8 ; countMOV AH, 7FH ; selectionMOV SI, OFFSET MEM-1 MOV DX, 01H ; port B

DISP1: MOV AL, AH OUT DX, AL DEC DX MOV AL, [BX+SI] OUT DX, AL CALL DELAY

ROR AH, 1INC DXDEC BXJNZ DISP1

0111 1111

SI

1. For 8 (eight) times1. Send data through port A2. Select a segment through port B

7-segment LED Display

MOV BX, 8 ; countMOV AH, 7FH ; selectionMOV SI, OFFSET MEM-1 MOV DX, 01H ; port B

ROR AH, 1INC DXDEC BXJNZ DISP1

DISP1: MOV AL, AH OUT DX, AL DEC DX MOV AL, [BX+SI] OUT DX, AL CALL DELAY

DISP PROC NEAR PUSHF PUSH AX PUSH BX PUSH DX PUSH SI

POP SI POP DX POP BX POP AX POPF RETDISP ENDP

Stepper Motor Interfaced to the 82C55

0

1

2

4

0011 = 3H 0110 = 6H

1100 = CH 1001 = 9H

Stepper Motor Interfaced to the 82C55

If CX > 8000H then spin right hand direction else spin left hand direction

Steeper Motor

If CX > 8000H then spin right hand direction else spin left hand direction

33H / 66H / CCH / 99H

7654 32100011 0011 = 33H0110 0110 = 66H1100 1100 = CCH1001 1001 = 99H

References

• Chapter 10.3 The Intel Microprocessors – by Barry B. Brey