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
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