13.22.6.1 Principle of Operation

The I²C interface uses two physical lines for communication:

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

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

The addressed I²C slave 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 slave or master, the I²C master takes action by either terminating the transaction by sending the stop condition, or by sending a repeated start to transfer more data.

The figure below illustrates the possible transaction formats and Transaction Diagram Symbols explains the transaction symbols. These symbols will be used in the following descriptions.

Figure 13-109. Basic I²C Transaction Diagram