汇编语言写大小写转换

DATA    SEGMENT
         STR DB 'Wrong word!Please input again:$'
DATA ENDS
CODE   SEGMENT
       ASSUME CS:CODE,DS:DATA
START: 
       MOV AH,01H      
       INT 21H
       MOV BL,AL       ;保存在BL中
       MOV DL,'-'        ;送‘-’号到DL
       MOV AH,02H      ;显示‘-’
       INT 21H          ;取回输入的字符                  
       MOV AL,BL  
       CMP AL,'a'       ;与‘a’比较                  
       JB  A           ;小于‘a’转A
       CMP AL,'z'       ;与 ‘z’比较
       JA  EXIT        ;大于‘z’转到EXIT  
       SUB AL,20H      ;取大写字母 
       MOV DL,AL      ;输出
       MOV AH,02H
       INT 21H
C:     MOV DL,0AH      ;输出换行
       MOV AH,02H
       INT 21H
       MOV DL,0DH      ;输出回车
       MOV AH,02H
       INT 21H
       JMP START       ;无条件转
A:     CMP AL,'A'
       JAE B