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1.What is EDID?

Extended display identification data (EDID) is a data structure provided by a digital display to describe its capabilities to a video source (e.g. graphics card orset-top box). It is what enables a modern personal computer to know what kinds of monitors are connected to it. EDID is defined by a standard published by the Video Electronics Standards Association (VESA). The EDID includes manufacturer name and serial number, product type, phosphor or filter type, timings supported by the display, display size, luminance data and (for digital displays only) pixel mapping data.

EDID data exchange is a standardized means for a display to communicate its capabilities to a source device. The premise of this communications is for the display to relay its operational characteristics, such as its native resolution, to the attached source, and then allow the source to generate the necessary video characteristics to match the needs of the display. This maximizes the functional compatibility between devices without requiring a user to configure them manually, thus reducing the potential for incorrect settings and adjustments that could compromise the quality of the displayed images and overall reliability of the system.

2.Where is EDID Utilized?

Generally, the source device will be a computer graphics card on a desktop or laptop PC, but provisions are in place for many other devices, including HDTV receivers and DVRs, DVD and Blu-ray Disc players, and even gaming consoles, to read EDID and output video accordingly. Originally developed for use between analog computer-video devices with VGA ports, EDID is also now implemented for DVI, HDMI, and DisplayPort.

3.What EDID Information is Exchanged Between Display and Source?

The base EDID information of a display is conveyed within a 128-byte data structure that contains pertinent manufacturer and operation-related data.

Vendor/Product Identification Block – The first 18 bytes identify the display manufacturer and product, including serial number and date of manufacture.

EDID Structure Version & Revision – The next two bytes identify the version and revision of the EDID data within the structure.

Basic Display Parameters/Features – The next five bytes define characteristics such as whether the display accepts analog or digital inputs, sync types, maximum horizontal and vertical size of the display, gamma transfer characteristics, power management capabilities, color space, and default video timing.

Color Characteristics – The next 10 bytes define the RGB color space conversion technique to be used by the display.

Established Timings – The next three bytes define the VESA-established video resolutions/timings that are supported by the display. Each bit represents an established timing such as 640x480/60. The last of the three bytes defines the manufacturer's reserved timing, if any.

Standard Timing Identification – The next 16 bytes define eight additional video resolutions supported by the display. These resolutions must adhere to standard VESA defined timings.

Detailed Timing Descriptions – The next 72 bytes are organized into four 18-byte blocks that describe additional video resolutions in detail, so that custom video timings/resolutions can be supported. The first of the four blocks is intended to describe the display's preferred video timing. The timing data can be structured according to the VESA GTF - Generalized Timing Formula or CVT - Coordinated Video Timings standards.

Extension Flag – EDID versions 1.3 and higher allow for additional 128-byte blocks of data to describe increased capabilities.

This byte indicates the number of additional extension blocks available. Various structures for these extension blocks have been defined, including DI-EXT - Display Information Extension, VTB-EXT - Video Timing Block Extension, and LS-EXT - Localized String Extension.

CEA-861 Extension – The most prevalent EDID extension is CEA-861, defined to support advanced capabilities of consumer devices incorporating HDMI.

4.EDID Issues

Display devices can have various levels of EDID implementation and, in some cases, they may lack EDID information altogether. Such inconsistencies can cause operational issues ranging from overscan and resolution problems, to the display device not displaying the source content at all.