Every byte on the SDA line must be 8 bits long. The number of bytes to be transmitted per transfer is unrestricted. Each byte has to be followed by an Acknowledge bit. Data is transferred with the Most Significant Bit (MSB) first. If a target cannot receive or transmit another complete byte of data until it has performed some other function, it can hold the clock line SCL low to force the host into a wait state (clock stretching). Data transfer then continues when the target is ready for another byte of data and release the clock line SCL.

Figure 8-11 Data Transfer on the I²C Bus