Procedure

.MODEL SMALL
.STACK 100

.DATA

    M1 DB 'ENTER A LOWERCASE CHAR: $'
    M2 DB 10, 13, 'UPPERCASE: '
    C1 DB ?, '$'

.CODE

MAIN PROC

    MOV AX, @DATA
    MOV DS, AX

    LEA DX, M1
    MOV AH, 9
    INT 21H

    MOV AH, 1
    INT 21H

    MOV C1, AL

    CALL CHECK

    LEA DX, M2
    MOV AH, 9
    INT 21H

    MOV AH, 4CH
    INT 21H

MAIN ENDP

CHECK PROC

    SUB C1, 20H
    RET

CHECK ENDP

END MAIN