27.3.2.1 Start and Stop Conditions

Two unique bus conditions are used for marking the beginning (Start) and end (Stop) of a transaction. The master issues a Start condition (S) by indicating a high-to-low transition on the SDA line while the SCL line is kept high. The master completes the transaction by issuing a Stop condition (P), indicated by a low-to-high transition on the SDA line while the SCL line is kept high.

Figure 27-4. Start and Stop Conditions

Multiple Start conditions can be issued during a single transaction. A Start condition that is not directly following a Stop condition is called a repeated Start condition (Sr).