;*************************;
;*  8253方式0計數器實驗  *;
;*************************;
code segment
	assume  cs:code
start: mov al,14h       ;設置8253通道0為工作方式2,二進制計數
	 mov dx,283h
	 out dx,al
	 mov dx,280h      ;送計數初值為0FH
	 mov al,0fh
	 out dx,al
lll:     in al,dx         ;讀計數初值
	 call disp        ;調顯示子程序
	 push dx  
	 mov ah,06h 
	 mov dl,0ffh
	 int 21h
	 pop dx
	 jz lll
	 mov ah,4ch       ;退出
	 int 21h
disp   proc near        ;顯示子程序
	 push dx
	 and al,0fh       ;首先取低四位
	 mov dl,al
	 cmp dl,9         ;判斷是否<=9
	 jle  num         ;若是則為'0'-'9',ASCII碼加30H
	 add dl,7         ;否則為'A'-'F',ASCII碼加37H
num:     add dl,30h
	 mov ah,02h       ;顯示
	 int 21h
	 mov dl,0dh       ;加回車符
	 int 21h
	 mov dl,0ah       ;加換行符
	 int 21h
	 pop dx
	 ret              ;子程序返回
    disp endp
    code ends
	end