def write_single_register(slave_id, address, value):
function = WriteSingleRegister()<EOL>function.address = address<EOL>function.value = value<EOL>return _create_request_adu(slave_id, function.request_pdu)<EOL>
Return ADU for Modbus function code 06: Write Single Register.

    :param slave_id: Number of slave.
    :return: Byte array with ADU.