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What is EDID and why is it so important in HDMI matrix switchers?

Release date:2021-09-10 Source:BeingHD Pageviews:-

Why do we need to learn about EDID? When we statistically and analyze the problem that the signal source is not displayed on the terminal display when the customer uses the HDMI matrix switcher and HDMI extender, most of the reasons are caused by EDID. Then, what is EDID? Let's take a look together.

EDID: Extended Display Identification Data ---- refers to the display device data transmitted in DDC communication.

Q1: What is EDID?

A1: The full name of EDID is Extended Display Identification Data (refers to the display device data transmitted in DDC communication). The EDID of VGA and DVI consists of 128 bytes in the main block. The EDID of HDMI adds an expansion block (128 bytes). The content of the expansion block is mainly audio Attribute-related, DVI and VGA have no audio, HDMI comes with audio, and the expansion block data specification is defined in accordance with the CEA-861x standard, which may increase to an integer multiple of 512 or 256 in the future.

It contains parameters related to the display and its performance, including supplier information, maximum image size, color settings, manufacturer presets, frequency range limitations, and strings of display name and serial number, etc. To put it vividly, EDID is a collection of ID cards, household registration books, skills certificates and other documents of the display. The purpose is to tell others who I am, where I come from, and what I can do.

Q2: Why use EDID?

A2: In order to allow PC or other image output devices to better identify display attributes

EDID did not exist in ancient times. In the ancient CRT period, there was no concept of EDID. Why did it exist later? Because with the development of display devices, there are more and more types of monitors, such as analog, digital, general screen, widescreen, 17-inch, 19-inch, 22-inch...This makes the PC dumbfounded, resolution and timing There are too many types, and each monitor cannot support all resolutions, so how do you know what resolution to give the monitor? Is the displayed effect the best? Not only that, but outputting a resolution at random may also damage the display hardware, which is too dangerous. As a result, EDID was ordered to act as the microphone before the display and PC. "Hello PC, I am A monitor, I can display N resolutions, the best resolution is XXX". "Hello monitor, I have received your message, and now I will output it to you at the best resolution." Now everyone understands, EDID is designed to allow PCs or other image output devices to better identify the attributes of the display.

Q3: I often hear comrades say "EDID information" for a while and "DDC information" for a while. So which statement is more accurate? What is the relationship between EDID and DDC?


A3: The full name of DDC is Display Data Channel. As the name implies, it is a channel. We can say that DDC is used to transmit EDID information, or that EDID information is transmitted through DDC, so the term "DDC information" is not accurate.

Q4: Is there only one EDID for each display?

A4: Not necessarily.

Nowadays, monitors are very powerful and usually provide multiple video interfaces, such as DVI, VGA, HDMI, Display Port, etc. The characteristics and bandwidth of each interface are different, so that the EDID of different interfaces is also different. Which interface is used, the PC reads the EDID of which interface. Our equipment mainly uses DVI, VGA, HDMI several interfaces. Since several formats of the VIDEO interface, such as PAL, NTSC, etc., have fixed resolution and field frequency, there is no need to use EDID, so they are not discussed.

Q5: What is the use of EDID for us?

A5: To answer this question, we must first clarify the application scenarios of our equipment, please see the picture below


connection-of-HDMI-matrix-swithcer

This is a typical application scenario. The PC or other input signal sends the video signal to HDMI matrix switchers. After a series of transmission or switching, the HDMI matrix switcher sends the video signal to the monitor or projector. That is to say, our HDMI matrix switchers is located between the PC and the monitor. First of all, at the input end, the HDMI matrix switchers needs to let the PC know that it can input video signals. In other words, the HDMI matrix switcher has to "cheat" the PC and make the PC think it is a monitor. If this is not the case, the PC may refuse to output any video signals (the VGA interface can also output without EDID). In addition, the HDMI matrix switcher also tells the PC which display sequence it supports. On the output side, when the HDMI matrix switcher needs to build its own output timing (such as the output card of a large-screen controller) instead of simply copying the input timing (such as various matrix HDMI matrix switchers), it needs to know the display timing supported by the display, so that The signal output by oneself can be displayed normally on the monitor. In these places, EDID comes into play. At the input end, the PC learns the display timing supported by the HDMI matrix switcher by reading the EDID on the HDMI matrix switcher, and similarly, the output end HDMI matrix switcher needs to read the EDID of the display to determine its own output timing.



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