王爽《汇编语言》问题7.9 将datasg段中每个单词的前4个字母改为大写字母

assume cs:codesg,ds:datasg

datasg segment

        db '1. display      '

        db '2. brows        '

        db '3. replace      '

        db '4. modify       '

datasg ends

stack segment

        dw 0,0,0,0, 0,0,0,0

stack ends

codesg segment

start:

        mov ax,datasg

        mov ds,ax

        mov di,0

        mov cx,4

        mov ax,stack

        mov ss,ax

        mov sp,10H

      s:

        push cx

        mov cx,4

      k:

        mov bl,[di+03]

        and bl,11011111B

        mov [di+03],bl

        inc di

        loop k

        pop cx

        add di,0cH

        loop s

              mov ax,4c00H

        int 21H

codesg ends

end start