2.1.1 Byte Format

All I²C communication is done in 9-bit segments. A byte is sent from a master to a slave or vice versa, followed by an Acknowledge sequence sent back. After the eighth falling edge of SCL, the device transmitting data on SDA changes that pin from an output to an input and reads the ACK value on the ninth clock pulse.

The clock signal is provided by the master. Data is valid to change while SCL is low and sampled on the rising edge of SCL. Changes on the SDA line while SCL is high define special bus conditions, such as a Start or Stop condition.