Video protocols such as HDMI, DVI and VGA use the I2C bus for a display control channel, as well as a data display channel.

For audio and video transmissions, the control channels are designed to prevent delays and jitter; losing an occasional packet is not considered or treated as a problem.

For video, there is a data display channel (DDC), which is based on I2C and is embedded in the video device. The DDC2B  version of the data display channel uses the ID1 pin of the VGA connector to connect to the data of the I2C bus. Normally, I2C is bidirectional and can support many bus masters. However, for video the DDC2B is unidirectional and supports only one bus master, the graphics adapter, which monitors the slave device.

Figure 1: Beagle I2C/SPI Protocol Analyzer

The Beagle I2C/SPI Protocol Analyzer is a non-intrusive device for monitoring and capturing data on the I2C or SPI bus. Using the right cables and connectors, you can observe and capture data from an embedded bus. You may find limitations with the availability of off-the-shelf cables, but with readily available connectors, such limitations are easy to work around.

The Total Phase DVI Break Cable makes monitoring easy. This is a standard 2 meter DVI-D single link cable (DVI-male to DVI-male) with an additional 5x2 0.100" pitch keyed box connector, which provides a easy access the Display Data Channel (DDC) lines with the Beagle I2C/SPI analyzer.  To use this cable with HDMI,  DVI to HDMI adapters can be used, which are inexpensive and easily obtained almost anywhere, including  Amazon.com.

	Figure 2: DVI Breakout Cable	Figure 3: HDMI – DVI Adapter

Do you have any questions about how else Total Phase tools can be used for  development, test and simulation? Feel free to contact us at  sales@totalphase.com and learn more about how our tools can make your projects easier