Extended display identification data
From Wikipedia, the free encyclopedia
Extended display identification data (EDID) is a data structure provided by a computer display to describe its capabilities to a graphics card. It is what enables a modern personal computer to know what kind of monitor is connected. 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 structure 1.0 was defined in 1994; version 1.1 followed in 1996, then 1.2, and 1.3 in 2000. All these define upwards compatible 128 byte structures. EDID structure 2.0 defines a new 256-byte structure.
The channel for transmitting the EDID from the display to the graphics card is usually the I²C bus. The combination of EDID and I²C is called the Display Data Channel version 2, or DDC2. The 2 distinguishes it from VESA's original DDC, which used a different serial format.
Before DDC and EDID were defined, there was no standard way for a graphics card to know what kind of display device it was connected to. Some VGA connectors in personal computers provided a basic form of identification by connecting one, two or three pins to ground, but this coding was not standardized.
The EDID is often stored in the monitor in a memory device called a serial PROM (programmable read-only memory) or EEPROM (electrically erasable PROM) that is compatible with the I²C bus.
Many software packages can read and display the EDID information, such as read-edid[1] and Powerstrip[2] for Microsoft Windows and XFree86 (which will output the EDID to the log if verbose logging is on (startx -- -logverbose 6)) for Linux and BSD unix. Mac OS X natively reads EDID information (see /var/log/system.log or hold down Cmd-V on startup) and programs such as SwitchResX[3] or DisplayConfigX[4] can display the information as well as use it to define custom resolutions.
Contents |
[edit] Enhanced EDID (E-EDID)
Enhanced EDID is based on the EDID version 1.3, but offers support of extensions, which enable EDID 2.0 to be supported as an extension. Data fields for preferred timing, range limits, monitor name are required in E-EDID. E-EDID also supports dual GTF, standard timings aspect ratio change.
With the use of extensions, E-EDID string can be lengthened up to 32KiBytes.
[edit] EDID Extensions assigned by VESA
- Timing Extension (00h)
- Additional Timing Data Block (CEA EDID Timing Extension) (02h)
- Video Timing Block Extension (VTB-EXT) (10h)
- EDID 2.0 Extension (20h)
- Display Information Extension (DI-EXT) (40h)
- Localized String Extension (LS-EXT) (50h)
- Microdisplay Interface Extension (MI-EXT) (60h)
- Display Transfer Characteristics Data Block (DTCDB) (A7h, AFh, BFh)
- Block Map (F0h)
- Display Device Data Block (DDDB) (FFh)
- Extension defined by monitor manufacturer (FFh): According to LS-EXT, actual contents varies from manufacturer. However, the value is later used by DDDB.
[edit] Limitations
Some graphics card drivers have historically coped poorly with the EDID, using only its standard timing descriptors rather than its Detailed Timing Descriptors (DTDs). Even in cases where the DTDs were read, the drivers are/were still often limited by the standard timing descriptor limitation that the horizontal/vertical resolutions must be evenly divisible by 8. This means that many graphics cards cannot express the native resolutions of the most common wide screen 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 expressible, the size of wide screen display must thus be a multiple of 16×9 pixels. For 1366×768 pixel Wide XGA panels the nearest resolution expressible in the EDID standard timing descriptor syntax is 1360×765 pixels. Specifying 1368 pixels as the screen width would yield an unnatural screen height of 769.5 pixels.
Many Wide XGA panels do not advertise their native resolution in the standard timing descriptors, instead offering only a resolution of 1280×768. Some panels advertise a resolution only slightly smaller than the native, such as 1360×765. For these panels to be able to show a pixel perfect image, the EDID data must be ignored by the display driver or the driver must correctly interpret the DTD and be able to resolve resolutions whose size is not divisible by 8. Special programs are available to override the standard timing descriptors from EDID data; PowerStrip for Microsoft Windows and SwitchResX for Mac OS X. Even this is not always possible however, as some vendors' graphics drivers (notably those of Intel) will not accept custom resolutions, which can make it all but impossible to use the screen's native resolution.
[edit] EDID 1.1 data format
Byte sequence
00–07: Header information
08–17: Complete serial number
08–09: Manufacturer ID
10–11: Product ID Code (little-endian)
12–15: Serial Number (little-endian)
16: Week of Manufacture
17: Year of Manufacture. Add 1990 to the value for actual year.
18: EDID Version Number
19: EDID Revision Number
20-24: Basic Display Parameters
20: VIDEO INPUT DEFINITION
bit 7: 0=analog, 1=digital
if bit 7 is digital:
bit 0: 1=DFP 1.x compatible
if bit 7 is analog:
bit 6-5: video level
00=0.7, 0.3, 01=0.714, 0.286, 10=1, .4 11=0.7, 0
bit 4: blank-to-black setup
bit 3: separate syncs
bit 2: composite sync
bit 1: sync on green
bit 0: serration vsync
21: Maximum Horizontal Image Size (in centimeters).
22: Maximum Vertical Image Size (in centimetres).
23: Display Gamma. Divide by 100, then add 1 for actual value.
24: Power Management and Supported Feature(s):
bit 7: standby
bit 6: suspend
bit 5: active-off/low power
bit 4-3: display type.
00=monochrome, 01=RGB colour, 10=non RGB multicolour, 11=undefined
bit 2: standard colour space
bit 1: preferred timing mode
bit 0: default GTF supported
25-34: CHROMA INFO
25: low significant bits for Red X (bit 7-6), Red Y (bit 5-4), Green X (bit 3-2), Green Y (bit 1-0).
26: low significant bits for Blue X (bit 7-6), Blue Y (bit 5-4), White X (bit 3-2), White Y (bit 1-0).
27–34: high significant bits for Red X, Red Y, Green X, Green Y, Blue X, Blue Y, White X, White Y.
To decode actual value, rearrange bits as follows:
High significant bits 7-0 for (channel), low significant bits for (channel).
Actual value is between 0.000 and 0.999, but encoded value is between 000h and 3FFh.
35: ESTABLISHED TIMING I
bit 7-0: 720×400@70 Hz, 720×400@88 Hz, 640×480@60 Hz, 640×480@67 Hz,
640×480@72 Hz, 640×480@75 Hz, 800×600@56 Hz, 800×600@60 Hz
36: ESTABLISHED TIMING II
bit 7-0: 800×600@72 Hz, 800×600@75 Hz, 832×624@75 Hz, 1024×768@87 Hz (Interlaced),
1024×768@60 Hz, 1024×768@70 Hz, 1024×768@75 Hz, 1280×1024@75 Hz
37: Manufacturer's Reserved Timing
00h for none
bit 7: 1152x870 @ 75 Hz (Mac II, Apple)
38–53: Standard Timing Identification. 2 bytes for each record.
First byte
Horizontal resolution. Multiply by 8, then add 248 for actual value.
Second byte
bit 7-6: Aspect ratio. Actual vertical resolution depends on horizontal resolution.
00=16:10, 01=4:3, 10=5:4, 11=16:9
bit 5-0: Vertical frequency. Adds 60 to get actual value.
54–71: Descriptor Block 1
54–55: Pixel Clock (in 10 kHz) or 0
If Pixel Clock is non null:
56: Horizontal Active (in pixels)
57: Horizontal Blanking (in pixels)
58: Horizontal Active high (4 upper bits)
Horizontal Blanking high (4 lower bits)
59: Vertical Active (in pixels)
60: Vertical Blanking (in vertical pixels/lines)
61: high significant bits for Vertical Active (4 upper bits)
high significant bits for Vertical Blanking (4 lower bits)
62: Horizontal Sync Offset (in pixels)
63: Horizontal Sync Pulse Width (in pixels)
64: Vertical Sync Offset (in lines) (4 upper bits)
Vertical Sync Pulse Width (in lines) (4 lower bits)
65: high significant bits for Horizontal Sync Offset (bit 7-6)
high significant bits for Horizontal Sync Pulse Width (bit 5-4)
high significant bits for Vertical Sync Offset (bit 3-2)
high significant bits for Vertical Sync Pulse Width (bit 1-0)
66: Horizontal Image Size (in mm)
67: Vertical Image Size (in mm)
68: high significant bits for Horizontal Image Size (4 upper bits)
high significant bits for Vertical Image Size (4 lower bits)
69: Horizontal Border
70: Vertical Border
71: Interlaced or not (bit 7)
Stereo or not (bit 6-5) ("00" means not)
Separate Sync or not (bit 4-3)
Vertical Sync positive or not (bit 2)
Horizontal Sync positive or not (bit 1)
Stereo Mode (bit 0) (unused if 6-5 are 00)
If Pixel Clock is null:
56: 0
57: Block type
FFh=Monitor Serial Number, FEh=ASCII string, FDh=Monitor Range Limits, FCh=Monitor name,
FBh=Colour Point Data, FAh, Standard Timing Data, F9h=Currently undefined, F8h=defined by manufacturer
58: Unknown
59–71: Descriptor block contents.
If block type is FFh, FEh, or FCh, the entire area is a text string.
If block type is FDh:
59–63:
Min Vertical frequency, Max Vertical frequency,
Min Horizontal frequency (in kHz), Max Horizontal frequency (in kHz), pixel clock (in MHz (multiply by 10 for actual value))
64–65: Secondary GTF toggle
If encoded value is 000A, bytes 59-63 are used. If encoded value is 0200, bytes 67–71 are used.
66: Start horizontal frequency (in kHz). Multiply by 2 for actual value.
67: C. Divide by 2 for actual value.
68-69: M (little endian).
70: K
71: J. Divide by 2 for actual value.
If block type is FBh:
59: W Index 0. If set to 0, bytes 60-63 are not used. If set to 1, 61–63 are assigned to white point index #1
64: W Index 1. If set to 0, bytes 65-68 are not used. If set to 2, 65–68 are assigned to white point index #2
White point index structure:
First byte
bit 3-2: low significant bits for White X (bit 3-2), White Y (bit 1-0)
Second to third byte: high significant bits for White X, White Y.
Fourth byte: Gamma. Divide by 100, then add 1 for actual value.
To decode White X and White Y, see bytes 25-34.
If block type is FAh:
59–70: Standard Timing Identification. 2 bytes for each record.
For structure details, see bytes 38-53.
72–89: Descriptor Block 2
90–107: Descriptor Block 3
108–125: Descriptor Block 4
126: Extension EDID Block(s). In EDID 1.1, it is ignored, and should be set to 0. In EDID 1.3, this is the number of
extension blocks which follow the first.
127: Checksum.
For example, here is a summary of the data reported by an Envision EN-775e monitor:
Monitor Name EPI EnVision EN-775e Monitor ID EPID775 Model EN-775e Manufacture Date Week 26 / 2002 Serial Number 1226764172 Max. Visible Display Size 32 cm × 24 cm (15.7 in) Picture Aspect Ratio 4:3 Horizontal Frequency 30–72 kHz Vertical Frequency 50–160 Hz Maximum Resolution 1280×1024 Gamma 2.20 DPMS Mode Support Active-Off Supported Video Modes: 640×480 140 Hz 800×600 110 Hz 1024×768 85 Hz 1152×864 75 Hz 1280×1024 65 Hz Monitor Manufacturer: Company Name Envision, Inc.
[edit] Extension Block Details
The CEA EDID Timing Extension was first introduced in EIA/CEA-861, and has since been updated several times, most notably with the -861B revision (which was version 3 of the extension, adding Short Video Descriptors and advanced audio capability/configuration information) and -861D (which is the most recent and contains updates to the audio segments).
Version 1 (as defined in -861) allowed the specification of video timings only through the use of 18-byte Detailed Timing Descriptors (as detailed in EDID 1.1 data format above). In all cases, the "preferred" timing should be the first DTD listed in a CEA EDID Timing Extension.
Version 2 (as defined in -861A) added the capability to designate a number of DTDs as "native" and also included some "basic discovery" functionality for whether the display device contains support for "basic audio", YCbCr pixel formats, and underscan.
Per Version 3 (from the -861B spec), there are two different ways to specify the timings of available DTV formats: via the use of 18-byte Detailed Timing Descriptors as in Version 1 & 2, and via the use of the Short Video Descriptor (see below).
Included in Version 3 are four new optional types of data blocks: Video Data Blocks (containing the aforementioned Short Video Descriptors), Audio Data Blocks (containing Short Audio Descriptors), Speaker Allocation Data Blocks (containing information about the speaker configuration of the display device), and Vendor Specific Data Blocks (which can contain information specific to a given vendor's use).
[edit] CEA EDID Timing Extension Version 3 data format
Byte sequence
00: Extension tag (which kind of extension block this is); 02h for CEA EDID
01: Revision number (Version number); 03h for Version 3
02: Byte number "d" within this block where the 18-byte DTDs begin. If no non-DTD data is present in this extension block, the value
should be set to 04h (the byte after next). If set to 00h, there are no DTDs present in this block and no non-DTD data.
03: Number of DTDs present, other Version 2+ information
bit 7: 1 if display supports underscan, 0 if not
bit 6: 1 if display supports basic audio, 0 if not
bit 5: 1 if display supports YCbCr 4:4:4, 0 if not
bit 4: 1 if display supports YCbCr 4:2:2, 0 if not
bit 3..0: total number of native formats in the DTDs included in this block
04: Start of Data Block Collection. If byte 02 is set to 04h, this is where the DTD collection begins. If byte 02 is set to another
value, byte 04 is where the Data Block Collection begins, and the DTD collection follows immediately thereafter.
The Data Block Collection contains one or more data blocks detailing video, audio, and speaker placement information about the display.
The blocks can be placed in any order, and the initial byte of each block defines both its type and its length:
bit 7..5: Block Type Tag (1 is audio, 2 is video, 3 is vendor specific, 4 is speaker allocation, all other values Reserved)
bit 4..0: Total number of bytes in this block following this byte
Once one data block has ended, the next byte is assumed to be the beginning of the next data block. This is the case until the byte
(designated in Byte 02, above) where the DTDs are known to begin.
Any Audio Data Block contains one or more 3-byte Short Audio Descriptors (SADs). Each SAD details audio format, channel number, and
bitrate/resolution capabilities of the display as follows:
SAD Byte 1 (format and number of channels):
bit 7: Reserved (0)
bit 6..3: Audio format code
1 = Linear Pulse Code Modulation (LPCM)
2 = AC-3
3 = MPEG1 (Layers 1 and 2)
4 = MP3
5 = MPEG2
6 = AAC
7 = DTS
8 = ATRAC
0, 15: Reserved
9 = One-bit audio aka SACD
10 = DD+
11 = DTS-HD
12 = MLP/Dolby TrueHD
13 = DST Audio
14 = Microsoft WMA Pro
bit 2..0: number of channels minus 1 (i.e. 000 = 1 channel; 001 = 2 channels; 111 = 8 channels)
SAD Byte 2 (sampling frequencies supported):
bit 7: Reserved (0)
bit 6: 192kHz
bit 5: 176kHz
bit 4: 96kHz
bit 3: 88kHz
bit 2: 48kHz
bit 1: 44kHz
bit 0: 32kHz
SAD Byte 3 (bitrate):
For LPCM, bits 7:3 are reserved and the remaining bits define bit depth
bit 2: 24 bit
bit 1: 20 bit
bit 0: 16 bit
For all other sound formats, bits 7..0 designate the maximium supported bitrate divided by 8kHz.
Any Video Data Block will contain one or more 1-byte Short Video Descriptors (SVDs). They are
decoded as follows:
bit 7: 1 to designate that this should be considered a "native" resolution, 0 for non-native
bit 6..0: index value to a table of standard resolutions/timings from CEA/EIA-861B:
1 640x480p @ 59.94/60Hz 4:3
2 720x480p @ 59.94/60Hz 4:3
3 720x480p @ 59.94/60Hz 16:9
4 1280x720p @ 59.94/60Hz 16:9
5 1920x1080i @ 59.94/60Hz 16:9
6 720x480i @ 59.94/60Hz 4:3
7 720x480i @ 59.94/60Hz 16:9
8 720x240p @ 59.94/60Hz 4:3
9 720x240p @ 59.94/60Hz 16:9
10 2880x480i @ 59.94/60Hz 4:3
11 2880x480i @ 59.94/60Hz 16:9
12 2880x240p @ 59.94/60Hz 4:3
13 2880x240p @ 59.94/60Hz 16:9
14 1440x480p @ 59.94/60Hz 4:3
15 1440x480p @ 59.94/60Hz 16:9
16 1920x1080p @ 59.94/60Hz 16:9
17 720x576p @ 50Hz 4:3
18 720x576p @ 50Hz 16:9
19 1280x720p @ 50Hz 16:9
20 1920x1080i @ 50Hz 16:9
21 720x576i @ 50Hz 4:3
22 720x576i @ 50Hz 16:9
23 720x288p @ 50Hz 4:3
24 720x288p @ 50Hz 16:9
25 2880x576i @ 50Hz 4:3
26 2880x576i @ 50Hz 16:9
27 2880x288p @ 50Hz 4:3
28 2880x288p @ 50Hz 16:9
29 1440x576p @ 50Hz 4:3
30 1440x576p @ 50Hz 16:9
31 1920x1080p @ 50Hz 16:9
32 1920x1080p @ 23.97/24Hz 16:9
33 1920x1080p @ 25Hz 16:9
34 1920x1080p @ 29.97/30Hz 16:9
0, 35 - 127 Reserved
A Vendor Specific Data Block (if any) contains as its first three bytes the vendor's IEEE
24-bit registration number, LSB first. It is usually followed by a three byte source
physical address, LSB first. The source physical address provides the CEC physical address for
upstream CEC devices. The remainder of the Vendor Specific Data Block is the "data payload",which
can be anything the vendor considers worthy of inclusion in this EDID extension block.
If a Speaker Allocation Data Block is present, it will consist of three bytes. The second and
third are Reserved (all 0), but the first contains information about which speakers are present in
the display device:
bit 7: Reserved (0)
bit 6: Rear Left Center / Rear Right Center present for 1, absent for 0
bit 5: Front Left Center / Front Right Center present for 1, absent for 0
bit 4: Rear Center present for 1, absent for 0
bit 3: Rear Left / Rear Right present for 1, absent for 0
bit 2: Front Center present for 1, absent for 0
bit 1: LFE present for 1, absent for 0
bit 0: Front Left / Front Right present for 1, absent for 0
Note that for speakers with right and left polarity, it is assumed that both
left and right are present.
"d": byte (designated in byte 02) where DTDs begin. 18-byte DTD strings continue for an unspecified
length (modulo 18) until a "00 00" is as the first bytes of a prospective DTD. At this point,
the DTDs are known to be complete, and the start address of the "00 00" can be considered to be "XX"
(see below)
"XX"-126: Post-DTD padding. Should be populated with 00h
127: Checksum.
[edit] References
- ^ read-edid software for Linux and Windows
- ^ Powerstrip for Windows (Shareware)
- ^ SwitchResX for Mac OS X shows EDID and customizes display timings
- ^ DisplayConfigX for Mac OS X shows EDID and customizes display timings
[edit] External links
- VESA BIOS Extensions/Display Data Channel Standard
- VESA ENHANCED EXTENDED DISPLAY IDENTIFICATION DATA – Implementation Guide
- EDID 1.2 on Flat Panels (in Appendix A)
[edit] Extensions
- VESA Video Timing Block Extension Data Standard (VTB-EXT)
- VESA Display Information Extension Block Standard (DI-EXT)
- VESA Enhanced EDID Localized String Extension Standard (LS-EXT)
