All About EDID

Engineer Data: All About EDID

​EDID is a term that you have likely seen or heard if you have been in the audio video industry for a while. Like HDCP (High-Bandwidth Digital Content Protection) it is commonly attributed to undesirable audio and video outputs.

So, what is EDID and why is it used?

Let’s start with some EDID history. Extended Display Identification Data (EDID) was introduced by the Video Electronics Standards Association (VESA) in August of 1994 with release of EDID v1.0. A few updates later and in September of 2000 VESA introduced Enhanced – EDID (E-EDID) v1.0, and as part of the new specification was EDID v1.3. The next, and latest, update was released in 2006 when we received E-EDID v2.0, and EDID v1.4. This is the current version of EDID that is used today.

Now that you know when it came out, we will explain what EDID is and why we need it. 

EDID is a message of information that comes from your output device that explains to your audio video equipment how to setup your audio and video signals. This message includes many specific technical settings and parameters that can precisely portray all supported signal formats. This is important so that your computer, Blu-Ray player, game console, audio receiver, or other devices that will send or repeat a signal (we refer to these devices as “source” devices) knows what type of signals are valid and will work with your output devices, which may include a TV, monitor, soundbar, or audio video input (we refer to these devices as “sink” devices). Without EDID you would have to make sure to set these devices manually, and if you messed up the settings you would not have a visible picture or sound may not be coming through to your devices. EDID set out to make installation of devices easier and allow easy changing of devices around a time when computers were now becoming more mobile. 

Now that we know a little about what EDID is and why we have it, what does an EDID message look like? I will forewarn you; it can be a little intimidating to understand at first, but AVPro is here to help make you more knowledgeable and make more technical features easy to understand and use.

Here is an EDID message that is sent to a source device from a TV:

​This probably does not make much sense to you, but to a source device you would have all the information you need to send it the highest resolution video, correct HDR support, and valid audio formats. Let’s look at some of the information provided in this EDID.
EDID is separated into sections we call EDID “blocks.” Each block is associated with a specific group of information, and different devices will include different blocks. A block is typically 128 Bytes in size, though some blocks can be larger, and the size is defined within their block header. The first half of the EDID contains the base EDID v1.3 or v1.4 blocks. This article is going to review the information contained in the base EDID. A future article will cover the other extension block that is included in this EDID.

Header Info:
     Manufacturer: GSM
     Product Code: 49352
     Serial Number: 16843009
     Week of Manufacture: 1
     Year of Manufacture: 2020
     EDID Version: 1.3

EDIDs all begin with a padded byte string and a header. The header tells you who the sink device (output) manufacturer is, and more information about the product, and finally the EDID version. In this case even though it is a newer display they are still using EDID v1.3. Some of the bytes in the EDID represent different settings when v1.3 compared to v1.4.

Basic Display Parameters:
     Video input parameters: Digital  Bit Depth: Undefined/Reserved
     Video Interface: Undefined
     Screen Size (mm): 160, 90
     Display Gamma: 2.20
     DPMS Standby Supported: false
     DPMS Sustpend Supported: false
     DPMS Active Off Supported: false
     Display Type/ Chroma Support: RGB 4:4:4 + YCrCb 4:4:4
     RGB 4:4:4 Support: true
     YCrCb 4:4:4 Support: true
     YCrCb 4:2:2 Support: false
     sRGB Colorspace: false
     Preferred timing mode specified in Block 1: true
     Continuous timings with GTF or CVT (only analog may be true): false

This section defines basic display parameters that describe the connection details and what type of signal format is supported. It describes analog or digital support, the color sampling support, and if the preferred resolution and timing is later defined in the detailing timing descriptor block 1.
Chromacity Coordinates:
     Red   0.63965, 0.33008
     Green 0.29980, 0.59961
     Blue  0.15039, 0.05957
     White 0.31250, 0.32910
Established Timings I & II:
     720x400 @ 70 Hz (VGA)
     640x480 @ 60 Hz (VGA)
     800x600 @ 60 Hz
     1024x768 @ 60 Hz

Standard Timings:
     Display mode 1:
     Resolution (horizontal): 640
     Aspect Ratio: 4:3
     Vertical Frequency: 60 Hz
     Display mode 2-8: …

Established and Standard Timings are a list of common older, and not as common in modern video systems, resolutions and timings. The EDID will tell you which of these timings are supported and which timings are unsupported.

Descriptor Blocks:
Block 1
     Descriptor type: Detailed Timing Block
     Index: 0x36
     Quick Info: 3840x2160 (Preferred Timing)
     Pixel Clock: 594.000 MHz
     Horizontal Active Pixels: 3840
     Horizontal Blanking Pixels: 560
     Horizontal Total Pixels: 4400
     Horizontal Front Porch (Sync Offset) Pixels: 176
     Horizontal Sync Pulse Width Pixels: 88
     Vertical Active Pixels: 2160
     Vertical Blanking Pixels: 90
     Vertical Total Pixels: 2250
     Vertical Front Porch (Sync Offset) Pixels: 8
     Vertical Sync Pulse Width Pixels: 10
     Image Size: 62.99 in x 35.43 in (1600 mm x 900 mm )
     Diagonal Size: 72.27 in (1835.76 mm)
     Signal Type: Progressive
     Stereo Mode: Unknown
     Sync Mode: Digital Sync, Separate
     Vertical Sync Polarity: positive
     Horizontal Sync Polarity: positive
Block 2
     Descriptor type: Detailed Timing Block
     Index: 0x48
     Quick Info: 1360x768
     Pixel Clock: 85.500 MHz
     Horizontal Active Pixels: 1360
     Horizontal Blanking Pixels: 432
     Horizontal Total Pixels: 1792
     Horizontal Front Porch (Sync Offset) Pixels: 64
     Horizontal Sync Pulse Width Pixels: 112
     Vertical Active Pixels: 768
     Vertical Blanking Pixels: 27
     Vertical Total Pixels: 795
     Vertical Front Porch (Sync Offset) Pixels: 3
     Vertical Sync Pulse Width Pixels: 6
     Image Size: 62.99 in x 35.43 in (1600 mm x 900 mm )
     Diagonal Size: 72.27 in (1835.76 mm)
     Signal Type: Progressive
     Stereo Mode: Unknown
     Sync Mode: Digital Sync, Separate
     Vertical Sync Polarity: positive
     Horizontal Sync Polarity: positive
Block 3
     Descriptor type: Display range limits
     Index: 0x5A
     Vertical Field Rate Range: 24 - 120 Hz
     Horizontal Line Rate Range: 30 - 255 kHz
     Maximum Pixel Clock Rate: 1190
     Extended timing information type: Default GTF

Block 4
     Descriptor type: Display name (ASCII)
     Index: 0x6C
     Display name: LG TV SSCR

The descriptor blocks above can be any one of a few different types of information. They are all 18 bytes long and can include detailed timing information (resolution and timing support), display range limits, a couple ASCII text blocks with different uses (commonly used to list the display name, which is how computers shows the name of the monitor in your display settings), and a few other useful types of descriptor blocks.

The last two pieces of information in the initial block is the number of extension blocks that follow the base EDID block and the block checksum, which is used to verify that the EDID was received correctly and that it was a valid built EDID block. This uses a modulo 256 checksum, which can be calculated by adding all the other byte values (bytes 0 to 126) together and dividing by 256. The remainder is the value that is set in the final byte (byte 127) as the checksum. The source device will calculated the checksum of the data and compare to the byte it received, if they match then it knows the EDID was received correctly.
​This is just the first block of the EDID. We will get more into the secondary blocks and how to manipulate and change EDID settings to provide the best audio video configuration in a future article as we continue this series in EDID information. This series will be culminated in a single larger resource that you will be able to use to examine your system EDIDs and provide help to understand the EDID settings in your equipment.
In addition to education reading materials and references, keep an eye out for new AVPro upgrades coming to enhance your EDID configuration tools and settings. This year we will be releasing some new changes to improve compatibility for the average integrator and providing more detailed information about EDIDs and tools to help the advanced integrator modify an EDID to tune their system to perfection.
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