8255练习
补充接口程序实现以下要求:
当开关合上,16个LED灯从上而下依次循环发光,每次只能点亮一个LED灯;
当开关打开,保持当前LED灯的点亮状态不变,下次开关合上时,从当前的LED灯开始点亮。
IOCON EQU 02D6H
IOA EQU 02D0H
IOB EQU 02D2H
IOC EQU 02D4H
CODE SEGMENT
ASSUME CS:CODE
START:
MOV AL,10001001B
MOV BX,0001H
MOV DX,IOCON
OUT DX,AL
A1:
MOV AL,BL
MOV DX,IOA
OUT DX,AL
MOV AL,BH
MOV DX,IOB
OUT DX,AL
MOV DX,IOC
IN AL,DX
TEST AL,00000010B;检查C口状态
JNZ A1
ROL BX,1
CALL DELAY
JMP A1
DELAY PROC
MOV CX,0FFFFH
A2:
NOP
LOOP A2
RET
DELAY ENDP
CODE ENDS
END START