汇编程序42：实验11 编写子程序

assume cs:code,ds:data
//锁定小写字母,从而改写,使用cmp与条件指令配合
data segment
    db "Beginner's All-purpose Symbolic Instruction Code.",0
data ends

code segment
    begin:
          mov ax,data
          mov ds,ax
          call letterc
          mov ax,4c00h
          int 21h
  letterc:
          mov si,0
          mov cx,30h
     main:
          mov al,ds:[si]
          cmp al,0
          je ok
          cmp al,61h
          jb next
          cmp al,7ah
          ja next
          and al,11011111b
          mov ds:[si],al
     next:      
          inc si
          loop main
       ok:
          ret
code ends

end begin