1. Lecture 14 Basic I/O Interface Presented By Dr. Shazzad Hosain Asst. Prof. EECS, NSU

2. 7-segment LED Display 00H – 03H are the I/O ports 7654 3210 0000 0000 Port A 0000 0001 Port B 0000 0010 Port C 0000 0011 Command Register 5 6 4 2 8 9 0 1 MEM 1.For 8 (eight) times 1.Send data through port A 2.Select a segment through port B OUT PORT, DATA OUT DX, AL

3. 7-segment LED Display 00H – 03H are the I/O ports 7654 3210 0000 0000 Port A 0000 0001 Port B 0000 0010 Port C 0000 0011 Command Register 5 6 4 2 8 9 0 1 MEM MOV BX, 8 ; count MOV AH, 7FH ; selection MOV 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, 1 INC DX DEC BX JNZ DISP1 0111 1111 SI 1.For 8 (eight) times 1.Send data through port A 2.Select a segment through port B

4. 7-segment LED Display MOV BX, 8 ; count MOV AH, 7FH ; selection MOV SI, OFFSET MEM-1 MOV DX, 01H ; port B ROR AH, 1 INC DX DEC BX JNZ 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 RET DISP ENDP

5. Stepper Motor Interfaced to the 82C55 0 1 2 4 0011 = 3H 0110 = 6H 1100 = CH 1001 = 9H

6. Stepper Motor Interfaced to the 82C55 If CX > 8000H then spin right hand direction else spin left hand direction Steeper Motor

7. If CX > 8000H then spin right hand direction else spin left hand direction 33H / 66H / CCH / 99H 7654 3210 0011 0011 = 33H 0110 0110 = 66H 1100 1100 = CCH 1001 1001 = 99H

8. References Chapter 10.3 The Intel Microprocessors – by Barry B. Brey