在dosbox窗口显示a~z

assume cs:code
stack segment
        db 128 dup (0)
stack ends
code segment
start:  mov ax,stack
        mov ss,ax
        mov sp,128
        mov ax,0b800h
        mov es,ax
        mov ah,'a'
   s:   mov es:[160*12+40*2],ah
        call delay
        inc ah
        cmp ah,'z'
        jna s
        mov ax,4c00h
        int 21h
delay:  push ax
        push dx
        mov dx,10h
        mov ax,0
   s1:  sub ax,1
        sbb dx,0
        cmp ax,0
        jne s1
        cmp dx,0
        jne s1
        pop dx
        pop ax
        ret
code ends
end start