Chipress

Serial Camera Control Bus (SCCB) is defined and deployed by OmniVision Technologies, Inc. Most of the functions in OmniVision image sensors can be controlled by SCCB.

The image sensor will be used as a slave device, and one master device will connect to at least one slave device; below is the 3-wire SCCB Functional Block Diagram:

If there is only one slave device, the SCCB can be implemented by only 2-wire, SIO_C and SIO_D; below is the 2-wire SCCB Functional Block Diagram:

In the 2-wire SCCB implementation, it requires one of the following two master control to facilitate the SCCB communication:

• The SIO_D data line must be in a tri-state mode which is supported by the master device
• The other method, if the master cannot have a tri-state mode, is to make the SIO_D drive to either 0 or 1 and broadcast there is a data transition with the slave device

Here is an interview question about the tri-state buffer in bus communication:

Q: Why do we need tri-state buffer in bus communication?

A: The tri-state buffer have a control signal, which can connect input to the output as wire, or as a very high resistance (theoretically open circuit). So, we could avoid the conflict by just allowing one source to connect to the bus. This idea is also used in the inout ports.