例4：写一个把字符串的所有大写字母改为小写的程序。设字符串以0结尾。
1 ;程序名:T3-12.ASM 2 ;功 能:说明根据某个条件控制的循环 3 DSEG SEGMENT 4 STRING DB 'HOW are yoU ! ',0 5 DSEG ENDS 6 ;-------------------------------------- 7 CSEG SEGMENT 8 ASSUME DS:DSEG,CS:CSEG 9 START: 10 MOV AX,DSEG 11 MOV DS,AX 12 13 MOV SI,OFFSET STRING 14 LOOPN:MOV AL,[SI] 15 OR AL,AL 16 JZ OK 17 CMP AL,'A' 18 JB NEXT 19 CMP AL,'Z' 20 JA NEXT 21 OR AL,20H 22 MOV [SI],AL 23 NEXT: INC SI 24 JMP LOOPN 25 OK: MOV AH,4CH 26 INT 21H 27 CSEG ENDS 28 END START
