35.8.5.1 Principle of Operation

The I²C interface uses two physical lines for communication:

• Serial Data Line (SDA) for data transfer
• Serial Clock Line (SCL) for the bus clock

A transaction starts with the I²C host sending the Start condition, followed by a 7-bit address and a direction bit (read or write to/from the client).

The addressed I²C client will then Acknowledge (ACK) the address, and data packet transactions can begin. Every 9-bit data packet consists of 8 data bits followed by a one-bit reply indicating whether the data was acknowledged or not.

If a data packet is Not Acknowledged (NACK), whether by the I²C client or host, the I²C host takes action by either terminating the transaction by sending the Stop condition, or by sending a repeated start to transfer more data.

The following figure illustrates the possible transaction formats. These symbols will be used in the following descriptions.