;*************************;
;*  8253方式0計數(shù)器實驗  *;
;*************************;
io8253a        equ 283h
io8253b        equ 280h
code segment
    assume  cs:code
start: mov al,14h       ;設(shè)置8253通道0為工作方式2,二進制計數(shù)
     mov dx,io8253a
     out dx,al
     mov dx,io8253b      ;送計數(shù)初值為0FH
     mov al,0fh
     out dx,al
lll:     in al,dx         ;讀計數(shù)初值
     call disp        ;調(diào)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 start