Understanding EDID: A Practical Guide

What does EDID stand for and why does it matter?

EDID stands for Extended Display Identification Data. This data is stored within a non-volatile memory known as EEPROM, which is part of the DVI display or HDMI sink.

The purpose of EDID is to exchange data between a display and a source device. This data includes operational attributes such as:

• Audio and video formats
• Lip sync delays
• Native resolution

This means that the source can generate video characteristics that match the needs of the display, without a user needing to intervene. In turn, it helps to describe supported functions when data sheets or operator manuals are out of date. Installers can use this to emulate the interaction of a display based on this data.

 If EDID is faulty or ignored, this increases the risk of incorrect settings, which could harm picture and audio quality, as well as overall reliability.

What is EDID and how does it work?

EDID communication dates back to the days of VESA, otherwise known as the Video Electronics Standards Association, who invented it to support Plug and Play. EDID is stored in the EEPROM chip on an HDMI sink or the input of an HDMI repeater device.

All HDMI compliant sink devices must implement EDID, which comprises two 128-byte blocks. The second is a CEA extension, which contains display-specific information.

EDID goes through the ‘HDMI initialisation sequence’ to transfer data:

1. Connection detection (hot plug detection through pins on the HDMI connector, sensing when a device is plugged in and readable)

2. Plug and play (data transfer through EDID)

3. High-bandwidth Digital Content Protection (HDCP – the process of authentication and protecting copyrighted audiovisual content).

EDID uses a Display Data Channel (DDC), which allows devices to assess capabilities and adjust themselves – like a DVD player with a monitor. Again, this saves users from manually configuring them and improves audiovisual quality.

How EDID enables AV device capability

EDID communicates between HDMI sources and sinks, for example, a games console and a television screen. This is particularly helpful for installers when we consider that data sheets, signage or operator manuals may no longer be available.

Instead, we can check display capabilities by looking at the EDID. This involves parsing EDID data into human-readable form, giving us a clear view of what is and what isn’t possible. For example, a TV monitor may support 3D mode, but a video source like a Blu-Ray player may not.

Installers can view EDID information shared across these channels such as:

• Formats
• Resolution
• Color
• Audio
• Latency

Common problems with EDID

Common problems with EDID relate to the HDMI source. For example, it may fail to:

• Read the data properly
• Read the data at all
• Finish reading the data.

This could result in the HDMI sink not supporting the video format, or the source not outputting optimal video quality.

Problems with extenders, splitters and repeaters

HDMI extenders may alter downstream EDID or change formats. Splitters may come hard-coded with an EDID, or even take the EDID of the first device connected via an HDMI cable.

Meanwhile, repeaters may cause problems. They may forward the downstream sink’s capabilities to the source unmodified, resulting in poor picture quality. Equally, they may fail to merge a large number of EDID video timing descriptors (SVSs) if there are several downstream EDIDs.

Problems with corrupted EDID

Other issues may be unsupported colour modes, as well as corrupted, poorly formed or incorrect EDIDs. This may affect video resolution, colour and aspect ratio, while audio may not be in the desired format.

What does an EDID emulator do?

Many problems can be solved with an HDMI EDID emulator. This is a form of troubleshooting. It may comprise other functions such as EDID ghosting (copying, cloning or learning EDID data from a display, like a projector).

Installers can test interoperability using tools like the Lindy VGA EDID Emulator. To check that an AV receiver, DVD or HDMI switch works with a display device, we can use a saved EDID on test equipment.

This is helpful at all stages of a home integration, including pre-installation checks, post-firmware diagnostics, and future-proofing systems.

EDID on repeaters and splitters

Repeater devices like AV receivers need the EDID to show the audio from the AVR. Meanwhile, the video should be the ‘intersection’ of the video data from the AVR and the sink device. The sequence should look like this:

1. Display device generates the hot plug, and the AV receiver’s source side reads audio data from the display EDID.

2. AV receiver incorporates data into the EDID and modifies video timings before forwarding this to the source device.

3. Source device reads the audio data from the EDID of the AV receiver’s sink side.

4. Source device outputs audio based on capabilities stated in the AV receiver’s EDID.

Alternatively, a splitter can be used. In this scenario, the EDID can be:

• An intersection of the two devices
• The EDID of the device that was first connected
• A forced provisioned EDID.

This time, the sequence would look like this:

1. One or more display devices generate a hot plug and the splitter source side reads video/audio information from the display EDID.

2. On the AV receiver, the splitter processes EDID and may pass the best common video and audio in its EDID, known as the intersection.

3. With the source device, the splitter asserts the hot plug, and the source reads video/audio data from the EDID of the splitter sink side.

4. The source device outputs video/audio based on the least common capabilities of the downstream device’s EDID, otherwise known as a union.

Best practices for reading and emulating EDID

Tools like a VGA or DVI EDID emulator are essential for testing digital video and audio systems. You can load EDID onto a test instrument for HDMI, either directly from a sink device or using a computer. To monitor DDC transactions, always check the reference manual.

The data will be stored in XML format, making it ideal for troubleshooting problems. Using tools like the 780 Series Handheld HDMI Video tester, you can identify problems such as firmware issues. If you’re using freeware software, ensure it can parse EDID files into human-readable formats. That way, technicians can explain any problems to clients with a description of supported features.

The testing process comprises:

• Reading EDID
• Error checking
• Verifying video and audio content
• Initiating hot plugs (e.g., USB power cables) and repeating.

Understanding EDID transport and interoperability

It’s important to be wary of capacitance constraints with HDMI cables. According to HDMI specification, in a DDC channel, levels cannot exceed 700 picofarads in a DDC channel. It’s common for there to be too much capacitance (the ability to store an electric charge).

This can lead to faulty EDID transmission, often caused by cable lengths. (For example, a 30-foot cable has 10 times the capacitance of a 3-foot cable.) To stay safe, remember to:

• Verify cable specifications before installing
• Check DDC behaviour
• Avoid long cable runs without compensation.

Why EDID still matters

Modern technology is giving consumers brighter visuals and crisper audio than ever before. But while state-of-the-art graphics cards or HDMI displays enable this, they’re useless without the right EDID handling.

Poorly formed EDID can lead to incorrect video resolution and audio formats, costing your business reputation and wasting time with callouts. That’s why it’s so important to check and test, using emulator systems like ATEN and Thunderbolt.

Always carry out these checks before deploying AV systems. They could be the difference between a happy and dissatisfied customer – while they could also prevent system issues in the long term.