Uppercase to Lowercase

.MODEL SMALL
.STACK 100H
.DATA
 
  M1 DB 0DH, 0AH, "ENTER THE UPER CASE LETTER::$"
  M2 DB 0DH, 0AH, "THE LOWER CASE LETTER IS::$"
  SUM DW 0

.CODE
  MAIN PROC
  MOV AX, @DATA
  MOV DS, AX

LEA DX,M1
MOV AH,9
INT 21H

MOV AH,1
INT 21H

MOV AL,A
ADD AL,20H
INT 21H

LEA DX,M2
MOV AH,9
INT 21H

MOV AH,2
MOV DL,BL
INT 21H

MOV AH, 4CH
INT 21H

MAIN ENDP
END MAIN