7章 7.9问题 将datasg段中每个单词前3个字母改为大写

不知为何 1437:0000 :没有大写
assume cs:code,ds:data,ss:stack
stack segment
   dw 0,0,0,0,0,0,0,0
stack ends
data segment
db '1. display      '
db '2. brows        '
db '3. replace      '
db '4. modify       '
data ends
code segment                                                   

start:    mov ax,data
          mov ds,ax
           
          mov ax,stack
          mov ss,ax
          mov sp,16   

          mov si,0      

           mov cx,4
         

  s1:     mov bx,3

          push cx            

          mov cx,3           

                  

   s:     mov al,[16+bx+si]
          and al,11011111b
          mov [16+bx+si],al   

          inc bx
        
          loop s        

          add si,16
          pop cx                    

          loop s1

          mov ax,4c00h
          int 21h
code ends
end start