Table of contents
I. Overview
HDMI, High-Definition Multimedia Interface, is a high-definition multimedia interface , which is an interface for computers, TVs and other related display devices.
2. Signal description
HDMI is divided into Source and Sink. Source is the signal source, which is the sending end of the HDMI signal. If we take a desktop computer as an example, the host is the Source and the monitor is the Sink (signal receiving end).
3. Signal definition
HDMI signals include TMDS, Clock, DDC (IIC), HPD, 5V, and CEC.
CEC, Consumer Electronics Control, is a feature of HDMI designed to allow users to command and control HDMI-connected devices by using only a remote.
This scene is rarely used. To be precise, the ones I have seen are basically useless, so they are all NC.
4. Handshake Process
1. Connect the HDMI cable to Source and Sink;
2. After Sink receives 5V, prepare EDID and pull HPD high when ready;
3. After Source detects that HPD is pulled high, it reads EDID through DDC;
4. Source analyzes the resolution supported by Sink through the read EDID and outputs an appropriate display stream;
5. There is a display screen on the Sink end.
Remark:
If the Source cannot read the EDID, it may also send out a data stream with any resolution. This behavior depends on the Source's approach.
5. Debugging steps
A. Debug based on the handshake process. If there is no screen display
1. Measure whether 5V voltage is received at the Sink terminal;
2. Measure whether the HPD signal is received at the Source end;
3. Use an oscilloscope to measure the DDC signal. Initially, you can use the scroll mode of the oscilloscope to see if there are dense clock and data signals. In a deeper level, you can use a protocol analyzer to read the detailed data on the link and check it with the EDID data.
4. Measure the TMDS and clock signals at the Source and Sink terminals. Normally, they are a densely packed set of waveforms.
B. If the screen flickers, it is mainly to confirm the signal quality.
1. If a conversion chip is used, whether the analog power and digital power are isolated;
2. Whether there is electromagnetic interference in the transmission path;
3. Check whether the trace is too long and has too many vias. Preliminarily check the impedance. If possible, you can use network classification tools to measure the impedance.
4. Check the interface for poor contact, etc.