22.5.3.7 Bus Collision During Message Bit Transmission

The most typical case of data collision occurs while the host attempts to transmit the device address byte, a data byte or an Acknowledge bit.

If the user software properly checks the bus state, it is unlikely that a bus collision will occur on a Start condition. However, because another host can, at the same time, check the bus and initiate its own Start condition, it is likely that SDAx arbitration will occur and synchronize the Start of two hosts. In this condition, both hosts begin and continue to transmit their messages until one host loses arbitration on a message bit. The SCLx clock synchronization keeps the two hosts synchronized until one loses arbitration. Figure 22-21 illustrates an example of the message bit arbitration.