Decode HDMI with USB Logic Analyzer and Pattern Generator
High Definition Multimedia Interface (HDMI) transmitting uncompressed video data and compressed or uncompressed digital audio data. HDMI has become the standard for a variety of consumer electronic products. When engineers and developers design the system with HDMI interface, they need to validate the HDMI physical layer to improve efficiency. The HDMI interface measurements are recommended in the early design stage.
Adam Taylor, an embedded design expert, uses Digilent Digital Discovery (136-8070) and Digital Discovery High-Speed Adapter to decode HDMI protocol in a thermal imaging application. The application is powered based on the Digilent Arty Z7 Zynq 7020 SoC Platform (136-8071) and FLIR Lepton. The image is output through HDMI port on Digilent Arty Z7-20. Digital Discovery is a combined logic analyzer and pattern generator instrument. The Digital Discovery High-Speed Adapter and impedance-matched probes can be used to connect and utilize the inputs and outputs for more advanced projects.
Thermal Imaging System
HDMI transmission mainly consists of three differential data channels and a differential clock. These signals use the Transition-Minimalized Differential Signalling (TMDS). In this project, Adam will decode these four signals. Other than these signals, the 19-pin HDMI connector includes five ground (GND) connections, a one-wire Consumer Electronics Control (CEC) bus, a two-wire Display Data Channel (DDC) bus that is essentially an I2C bus, a Hot Plug Detect (HPD) signal, a 5V signal capable of delivering up to 50mA, and one reserved (RES) pin.
To monitor the differential clock and data channels, Adam uses the High-Speed adapter, connected to channels 0 through 23. He also needs an HDMI breakout block, which connects to the end of the HDMI cable, allowing us to access the video signals. When he uses the High-Speed Adapter, each of the signals has a corresponding ground pin to ensure the best signal integrity. With the High-Speed Adapter for the Digital Discovery, he can sample signals at up to 800 mega samples per second (MS/s) using 8 bits. As he only needs four signals for the Data and Clock, this is exactly what we are going to do. When the HDMI breakout connector was connected to the HDMI output cable, and then to the Digital Discovery, the HDMI transmission can be captured.
Connect the HDMI breakout with Digital Discovery High-Speed Adapter and Digital Discovery
Stack the High-Speed Adatper on Digital Discovery
Adam examines the data shows the HDMI differential clock and data channels in the Logic Analyzer of Digilent Waveforms software application.
HDMI Differential Data and Clock Timing Diagram
The project details are available at Digilent Project Page.