The PCA9511 is a are hot swappable I2C-bus and SMBus buffer that allows I/O card insertion into a live backplane without corrupting the data and clock buses. Control circuitry prevents the backplane from being connected to the card until a STOP command or bus idle occurs on the backplane without bus contention on the card. When the connection is made, the PCA9511 provides bidirectional buffering, keeping the backplane and card capacitances isolated.