code segment
    assume cs:code,ds:code
start:
        push cs
    	pop ds
    
     	mov ax,data
	mov ds,ax
	lea si,ledtab

	mov al,81h
	mov dx,203h
	out dx,al;初始化控制字
	
  
        mov dx,202h
	mov al,0fh
	out dx,al;判斷有無按鍵，使所有列線為低電平
	in al,dx;讀取行值
	and al,0fh
	cmp al,0fh
	jz exit;無按鍵閉合結束程序，即跳出


	call delay;延時12ms消抖


	mov dx,202h
	mov al,0fh
	out dx,al;判斷有無按鍵，使所有列線為低電平
	in al,dx;讀取行值
	and al,0fh
	cmp al,0fh
	jz exit;無按鍵閉合結束程序
	


	mov bl,0efh;初始化列碼
	mov bh,0;初始化列計數器

again:	mov dx,202h
	mov al,bl
	out dx,al;輸出列碼
	in al,dx;讀取行值
	and al,0fh
	cmp al,0fh
	jz next;該列無鍵閉合，準備下一列掃描

	cmp al,0eh;判斷該列是否第一個鍵閉合
	jnz two
	mov al,0
	jmp free
two:cmp al,0dh;判斷該列是否是第二個鍵閉合
	jnz three
	mov al,1
	jmp free
three:cmp al,0bh;判斷該列是否是第三個鍵閉合
      	jnz four
	mov al,4
	jmp free
four:	cmp al,07h;判斷該列是否是第四個鍵閉合
	jnz next
	mov al,7
free:	push ax
wait1:  mov dx,202h;判斷按鍵是否結束
	mov al,0fh
	out dx,al;判斷有無按鍵，使所有列線為低電平
	in al,dx;讀取行值
	and al,0fh
	cmp al,0fh


	jnz wait1
	pop ax

      
	add al,bh; ;此時al中存放要顯示的值掃描鍵值+列計數值
	
	mov ah,0
	add si,ax;將顯示值設置為相應的段碼

	mov al,[si]
	mov dx,200h
	out dx,al;送到端口顯示
	
    	mov al,08h
        mov dx,202h
        out dx,al;設置位碼
    
next:	inc bh;列計數值加1
	rol bl,1 ;列碼循環左移一位
	cmp bl,0feh;判斷該輪鍵掃描是否結束
	jnz again
exit:mov ah,4ch
     	int 21h


delay proc near
	push bx
	push cx
	mov bx,2000
del1:mov cx,5000
del2:loop del2
	dec bx 
	jnz del1
	pop cx
	pop bx
	ret
delay endp

;定義數據段
data segment
 ledtab db 3fh,06h,5bh,4fh,66h,6dh,7dh,07h,7fh,6fh
data ends

code ends
end start