The Two-Wire Interface (TWI) is a bidirectional, two-wire communication interface (bus) with a Serial Data Line (SDA) and a Serial Clock Line (SCL).

The TWI bus connects one or several client devices to one or several host devices. Any device connected to the bus can act as a host, a client, or both. The host generates the SCL by using a Baud Rate Generator (BRG) and initiates data transactions by addressing one client and telling whether it wants to transmit or receive data. The BRG is capable of generating the Standard mode (Sm) and Fast mode (Fm, Fm+) bus frequencies from 100 kHz up to 1 MHz.

The TWI will detect Start and Stop conditions, bus collisions, and bus errors. Arbitration lost, errors, collision, and clock hold are also detected and indicated in separate status flags available in both Host and Client modes.

The TWI supports multi-host bus operation and arbitration. An arbitration scheme handles the case where more than one host tries to transmit data at the same time. The TWI also supports Smart mode, which can auto-trigger operations and thus reduce software complexity. The TWI supports Quick Command mode, where the host can address a client without exchanging data.