Extended Display Identification Data ( EDID ) is a metadata format for display devices to illustrate its ability to video sources (eg graphics card or decoder). The format of the data is determined by the standards published by the Video Electronics Standards Association (VESA).
EDID data structures include manufacturer name and serial number, product type, phosphor type or filter, time settings supported by display, display size, data lighting and (for digital display only) pixel mapping data.
DisplayID is a VESA standard targeted to replace EDID and E-EDID extensions with uniform formats suitable for PC monitors and consumer electronics devices.
Video Extended Display Identification Data
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EDID structure versions range from v1.0 to v1.4; all of these define a compatible 128-byte compatible structure upwards. The EDID v2.0 structure defines a new 256-byte structure, but has subsequently been abandoned and replaced by v1.3 that supports multiple expansion blocks. HDMI version 1.0-1.3c uses EDID structure v1.3.
Before Display Data Channel (DDC) and EDID are defined, there is no standard way for the graphics card to know what kind of connected display device is. Some VGA connectors on personal computers provide the basic form of identification by connecting one, two or three pins to ground, but the encoding is not standardized.
The channel to transmit EDID from view to graphics card is usually IÃ,ÂC-bus, defined in DDC2B (DDC1 uses a different serial format that never gained popularity).
EDID is often stored on a monitor in a memory device called serial PROM (programmable read-only memory) or EEPROM (an electrically removable PROM) and can be accessed via IÃ,ÂC-bus at address 0xA0. PROM EDID can often be read by the host PC even though the screen itself is turned off.
Many software packages can read and display EDID information, such as read-down for Linux and DOS, PowerStrip for Microsoft Windows and XFree86 for Linux and BSD unix. Mac OS X originally reads EDID information and programs such as SwitchResX or DisplayConfigX can display information and use it to specify a custom resolution.
Enhanced EDID is introduced at the same time as E-DDC; it introduces the EDID 1.3 version structure that supports multiple extension blocks and EDID version 2.0 structures that are no longer in use (although it can be backed up as extensions). Data fields for the selected time, reach limits, and monitor names are required in E-EDID. E-EDID also supports double GTF timing and aspect ratio change.
With the use of extensions, the E-EDID string can be extended to 32 KBytes.
EDID extension set by VESA
- Extension Time (00h)
- Additional Time Data Block (ADA EDID Time Extension) (02h)
- Video Block Time Extension (VTB-EXT) (10h)
- EDID 2.0 extension (20jt)
- Extension Display Information (DI-EXT) (40h)
- Local String String (LS-EXT) (50h)
- Microdisplay Interface Extension (MI-EXT) (60jt)
- Data Transfer Characteristics Display (DTCDB) (A7h, AFh, BFh)
- Map Block (F0h)
- Show Device Data Block (DDDB) (FFh)
- Extensions are determined by the monitor manufacturer (FFh): According to LS-EXT, the actual content varies from the manufacturer. However, its value is then used by DDDB.
Maps Extended Display Identification Data
Revision history
- August 1994, standard version of DDC 1 - EDID structure v1.0.
- April 1996, EDID standard version 2 - EDID v1.1 structure.
- 1997, EDID standard version 3 - EDID structure v1.2 and v2.0
- February 2000, Standard Release E-EDID A, v1.0 - EDID structure v1.3, EDID structure v2.0 not used anymore
- September 2006 - Standard Release E-EDID A, v2.0 - EDID structure v1.4
Limitations
Some graphics card drivers have historically been overcome badly with EDID, using only standard timing descriptor rather than Detailed Time Explanation (DTD). Even in cases where DTD is read, drivers are still often limited by standard timing constraints that the horizontal/vertical resolution should be shared evenly by 8. This means that many graphics cards can not express the most common native resolution of widescreen flat panel displays and liquid crystal display televisions. The number of vertical pixels is calculated from the horizontal resolution and the selected aspect ratio. To be fully recognizable, the widescreen size must be a multiple of 16 × 9 pixels. For 1366ÃÆ'â € "768 pixels XGA Panel The widest resolution width that can be expressed in the EDID standard timing decryption syntax is 1360ÃÆ'â €" 765 pixels, usually leading to 3 pixels thin black bars. Specifying 1368 pixels because the width of the screen will result in an unnatural screen height of 769.5 pixels.
Many Wide XGA panels do not advertise their native resolution in standard timing descriptor, but offer only 1280ÃÆ'â € "768 resolution. Some panels advertise a resolution that is only slightly smaller than the original, such as 1360ÃÆ'â €" 765. For this panel to display images perfect pixels, EDID data must be ignored by the display driver or the driver should interpret the DTD correctly and can resolve resolutions that can not be shared by 8. Special programs are available to replace the standard timing descriptions of the EDID data. In fact this is not always possible, as some graphics driver vendors (especially those from Intel) require special registry hacks to apply special resolutions, which can make it very difficult to use native screen resolution.
EDID 1.4 data format
When used for other descriptors, the pixel clock and some other bytes are set to 0:
The type of descriptor currently specified is:
- 0xFF: Show serial number (ASCII text)
- 0xFE: Unspecified text (ASCII text)
- 0xFD: Display coverage limit. 6- or 13-bytes (with additional time) binary information.
- 0xFC: Display name (ASCII text).
- 0xFB: Additional white dot data. 2ÃÆ'â € "5-byte descriptor, filled with
0A 20 20. - 0xFA: Additional standard time identifier. 6ÃÆ'â € "2-byte descriptor, filled with
0A. - 0xF9 Display Color Management (DCM).
- 0xF8 CVT 3-Byte Timing Codes.
- 0xF7 Additional Standard Time 3.
- 0x10 The puppet identifier.
- 00-0x0Fh Manufacturer provides encryption.
Blok ekstensi EIA/CEA-861
The CEA EDID Time Extension was first introduced in EIA/CEA-861, and has since been updated several times, most notably with the -861B revision (which is version 3 of the extension, adding Short Video Descriptor and advanced audio capability/configuration information)), 861D (published in July 2006 and contains updates for the audio segment), -861E, and -861F published on June 4, 2013. According to Brian Markwalter, senior vice president, research and standards, CEA, -861F "Includes a number of important improvements , including support for multiple Ultra HD video formats and widescreen and additional colorimetric schemes. "
The latest version, CTA-861-G, originally published in November 2016, was made available for free in November 2017 after some changes were required due to a trademark complaint.
Version 1 (as defined in -861) allows video timing specifications only through the use of 18-byte Detailed Timing Descriptors (DTD) (as described in the EDID 1.3 data format above). In all cases, the "preferred" time selection shall be the first DTD registered in the CEA EDA Time Extension.
Version 2 (as defined in -861A) adds the ability to assign multiple DTDs as "native" and also includes some basic "discovery" functions for whether the display device contains support for "basic audio", YCbCr pixel format, and underscan.
Version 3 (from the -861B specification) allows two different ways to determine which digital TV format timings are available: As in Version 1 & amp; 2 by using an 18-byte DTDS, or by using the Short Video Descriptor (SVD) (see below). HDMI 1.0 -1.3c uses this version.
Source of the article : Wikipedia
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