The TWI, two-wire control interface is compatible with the I²C interface from Philips. It provides a very simple and concise way to exchange control and data information between multiple devices. The Blackfin implementation supports both master and slave operation, and also supports transmission speeds up to 400kbits per second. The only two lines involved here are the SCL and SDA, nominally the clock and the data lines. They comprise the interface and the phase differences between those data streams determining the mode of operation that you’re in at a given point in time.