Uppercase to lowercase

.model small
.data

msg1 db 'Enter a letter: $'
msg2 db 'Letter in lowercase: $'


A db ?


.code
main proc
    mov ax, @data
    mov ds, ax

    lea dx,msg1
    mov ah, 9
    int 21h

    mov ah,1
    int 21h

    mov A, al
    int 21h

    mov ah, 2
    mov dl, 0ah ;new line
    int 21h
    mov dl, 0dh ;remove space
    int 21h


    add A, 32
    int 21h


    mov ah, 9
    lea dx,msg2
    int 21h

    mov ah, 2
    mov dl,A
    int 21h

         main endp
end main