Uppercase to lower case

.model small
.stack 100h
.data
msg1 db 'Enter a uppercase leeter: $'
msg2 db 10,13,'In lowercse it is: $'
.code
main proc

    mov ax,@data
    mov ds,ax

    mov ah,9
    lea dx,msg1
    int 21h

    mov ah,1
    int 21h
    mov bl,al

    add bl,32

    mov ah,9
    lea dx,msg2
    int 21h

    mov ah,2
    mov dl,bl
    int 21h


    exit:
    mov ah,4ch
    int 21h
    main endp
end main