def METHOD_NAME(slave_id, req_pdu):
    """ Return request ADU for Modbus RTU.
    :param slave_id: Slave id.
    :param req_pdu: Byte array with PDU.
    :return: Byte array with ADU.
    """
    first_part_adu = struct.pack('>B', slave_id) + req_pdu
    return first_part_adu + get_crc(first_part_adu)