The LTC4301L hot swappable, 2-wire bus buffer allows I/O card insertion into a live backplane without corruption of the data and clock busses. In addition, the LTC4301L SDAIN and SCLIN pins are compatible with systems with pull-up voltages as low as 1V. Control circuitry prevents the backplane from being connected to the card until a stop bit or a bus idle is present. When the connection is made, the LTC4301L provides bidirectional buffering, keeping the backplane and card capacitances isolated.