PCF8574_BASE_ADDR
slave_addr = (PCF8574_BASE_ADDR | ioport->chip_num);
PCF8574_BASE_ADDR | ioport->chip_num, buf, 1);
slave_addr = (PCF8574_READ_BIT | PCF8574_BASE_ADDR |
PCF8574_BASE_ADDR | ioport->chip_num, buf, 1);