The bidirectional control channel in the FPD-Link III devices implements I2C-compatible bus arbitration in the proxy I2C Controller implementation. When sending a data bit, each I2C Controller senses the value on the SDA line. If the Controller sends a logic 1 but senses a logic 0, the Controller loses arbitration. The Controller will stop driving SDA and retry the transaction when the bus becomes idle. Thus, multiple I2C Controllers may be implemented in the system.

For example, there might also be a local I2C Controller at each camera. The local I2C Controller could access the image sensor and EEPROM. The only restriction would be that the remote I2C Controller at the camera should not attempt to access a remote Target through the BCC that is located at the host controller side of the link. In other words, the control channel should only operate in camera mode for accessing remote Target devices to avoid issues with arbitration across the link. The remote I2C Controller should also not attempt to access the deserializer registers to avoid a conflict in register access with the Host controller.

If the system does require Controller-Target operation in both directions across the BCC, some method of communication must be used to ensure only one direction of operation occurs at any time. The communication method could include using available R/W registers in the deserializer to allow Controllers to communicate with each other to pass control between the two Controllers. An example would be to use register 0x18 or 0x19 in the deserializer as a mailbox register to pass control of the channel from one Controller to another.