.model small
.DATA
Old_09h dw 0,0

.code
.386

New09h:
    mov ah, 02h
    mov dl, 'A'
    int 21h
    jmp dword ptr cs:Old_09h

Init:
    mov ah, 09h
    mov dx, offset Msg
    int 21h
    mov ax, 3509h
    int 21h
    mov Old_09h, bx
    mov Old_09h+2, es
    mov ax, 2509h
    lea dx, New09h
    int 21h

end