This register contains the address of the external client device. When this bit field is written, the TWI will issue a Start condition, and the shift register performs a byte transmit operation on the bus depending on the bus state.

This register can be read at any time without interfering with the ongoing bus activity since a read access does not trigger the host logic to perform any bus protocol related operations.

The host control logic uses the bit 0 of this register as the R/W direction bit.