Assembly program to convert uppercase into lower and vice versa

.MODEL SMALL
.DATA

MSG DB 0DH,0AH, ' ENTER THE STRING :-----> : $'

MSG2 DB 0DH,0AH, ' YOUR STRING IS :-----> : $'

STR1 DB 255 DUP(?) ONE DB ? TWO DB ?

.CODE BEGIN:
MOV AX,@DATA
MOV DS,AX

LEA DX,MSG
MOV AH,09H INT 21H
LEA SI,STR1
MOV AH,01H
READ: INT 21H

MOV BL,AL
CMP AL,0DH
JE DISPLAY

XOR AL,20H
MOV [SI],AL
INC SI
;CMP BL,0DH
JMP READ

DISPLAY:
MOV AL,'$'
MOV [SI],AL
LEA DX,MSG2
MOV AH,09H
INT 21H
LEA DX,STR1
MOV AH,09H
INT 21H
; MOV AH,4CH
; INT 21H
.EXIT END

BEGIN ;**********************************OUTPUT****************************** ;
ENTER THE STRING :-----> SAMIR nihar KIRTAN

YOUR STRING IS :-----> samir NIHAR kirtan