怎么想也不知道为什么？那位大神解决下？？？？？？

assume cs:code,ds:data,ss:stack
       data segment
       db'ibm             '
       db'dec             '
       db'dos             '
       db'vax             '
       data ends
      
       stack segment
       dw 0,0,0,0,0,0,0,0
       stack ends
      
       code segment
       start: mov ax,stack
              mov ss,ax
              mov sp,16
              mov ax,data
              mov ds,ax
            
              mov bx,0
            
              mov cx,4
        s0:   push cx
              mov si,0
              mov cx,3
        s:    mov al,[bx+si]
              and al,11011111b
              mov [bx+si],al
              inc si
              loop s
            
              add bx,16
              pop cx
              loop s0
            
              mov ax,4c00h
              int 21h
        code ends
        end start