8255A-LED

DATA SEGMENT
	PORTA EQU 280H		;A端口地址
	PORTB EQU 281H		;B端口地址
	PORTD EQU 283H		;命令口地址
DATA ENDS

CODE SEGMENT
	ASSUME CS:CODE,DS:DATA
START:
	MOV	AX, DATA
	MOV	DS, AX
	MOV	DX, PORTD
	MOV	AL, 10010000B
	OUT		DX,AL
	MOV	DX, 281H 
	MOV	AL, 00H
	OUT		DX, AL

WAIT1:
	MOV	DX, PORTA
	IN	AL, DX
	AND	AL, 11111111B
	JZ	WAIT1

;从最低位向最高位逐位检验
	MOV	CX, 8
	MOV	BL, 1
LP1:
	MOV	DL,AL
	AND	DL,BL
	JNZ LED
	SHL		BL,1H
	LOOP LP1

LED:
	MOV	AL, DL
LP2:
	MOV	DX,	PORTB
	OUT		DX,AL
	CALL DELAY
	ROR		AL, 1		;循环右移
	JMP LP2

DELAY PROC
	PUSH BX
	PUSH CX
	MOV	CX, 04FFFH
DL1:
	MOV	BX, 00FFH
DL2:
	DEC BX
	JNZ DL2
	LOOP DL1
	POP CX
	POP BX
	RET
DELAY ENDP

CODE ENDS
END START