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'''E'''xtended '''D'''isplay '''ID'''entification is data about the monitor, which the monitor provides to the video card. EDID is ''the'' programmatical way to check if a video mode is supported. However, this procedure is rather complex. (See [[Getting VBE Mode Info|VBE]]
== Reading EDID ==
The first step
<
mov ax, 0x4f15
mov bl, 0x01
int 0x10
;AL = 0x4F if function supported
;AH = status (0 is success, 1 is fail)
;ES:DI contains the EDID
</syntaxhighlight>
Note that this code will only run in [[Real Mode]] or
== EDID Data ==
{{stub}}
'''EDID record:'''
{| class="wikitable"
|-
! Offset (Bytes)
! Length
! Description
|-
| 00h
| 8 Bytes
| Padding
|-
| 08h
| 1 Word
| Manufacture ID (Big-Endian)
|-
| 0Ah
| 1 Word
| EDID ID code
|-
| 0Ch
| 1 DWord
| Serial Number
|-
| 10h
| 1 Byte
| Manufacture Week
|-
| 11h
| 1 Byte
| Manufacture Year
|-
| 12h
| 1 Byte
| EDID Version
|-
| 13h
| 1 Byte
| EDID Revision
|-
| 14h
| 1 Byte
| Video Input Type
|-
| 15h
| 1 Byte
| Max Horizontal Size (cm)
|-
| 16h
| 1 Byte
| Max Vertical Size (cm)
|-
| 17h
| 1 Byte
| Gama Factor
|-
| 18h
| 1 Byte
| DPMS Flags
|-
| 19h
| 10 Bytes
| Chroma Information
|-
| 23h
| 1 Byte
| Established Timings 1
|-
| 24h
| 1 Byte
| Established Timings 2
|-
| 25h
| 1 Byte
| Manufacture's Reserved Timings
|-
| 26h
| 8 Words
| Standard Timing Identification
|-
| 36h
| 18 Bytes
| Detailed Timing Description 1
|-
| 48h
| 18 Bytes
| Detailed Timing Description 2
|-
| 5Ah
| 18 Bytes
| Detailed Timing Description 3
|-
| 6Ch
| 18 Bytes
| Detailed Timing Description 4
|-
| 7Eh
| 1 Byte
| Unused
|-
| 7Fh
| 1 Byte
| Checksum (Low Byte of 16-bit sum of 00-7Eh)
|}
'''Video Input Type:'''
{| class="wikitable"
|-
! Bit(s)
! Description
|-
| 0
| Separate Sync
|-
| 1
| Composite Sync
|-
| 2
| Sync on green
|-
| 3-4
| Unused?
|-
| 5-6
| Voltage Level
|-
| 7
| Digital Signal
|}
'''DPMS Flags:'''
{| class="wikitable"
|-
! Bit(s)
! Description
|-
| 0-2
| Unused?
|-
| 3
| Display Type (1=RGB)
|-
| 4
| Unused?
|-
| 5
| Active Off Supported
|-
| 6
| Suspend Supported
|-
| 7
| Standby Supported
|}
'''Chroma Information:'''
{| class="wikitable"
|-
! Byte
! Description
|-
| 0
| Green X'/Y' and Red X'/Y'
|-
| 1
| White X'/Y' and Blue X'/Y'
|-
| 2
| Red Y
|-
| 3
| Red X
|-
| 4
| Green Y
|-
| 5
| Green X
|-
| 6
| Blue Y
|-
| 7
| Blue X
|-
| 8
| White Y
|-
| 9
| White X
|}
'''Detailed Timing Description:'''
{| class="wikitable"
|-
! Byte
! Description
|-
| 0
| Horizontal Frequency (kHz)
|-
| 1
| Vertical Frequency (Hz)
|-
| 2
| Horizontal Active Time
|-
| 3
| Horizontal Blanking Time
|-
| 4
| Horizontal Active Time / Horizontal Blanking Time
|-
| 5
| Vertical Active time
|-
| 6
| Vertical Blanking Time
|-
| 7
| Vertical Active Time / Vertical Blanking Time
|-
| 8
| Horizontal Sync Offset
|-
| 9
| Horizontal Sync Pulse-width
|-
| 10
| Vertical Sync Offset / Vertical Sync Pulse-width
|-
| 11
| Vertical/Horizontal Sync Offset / Pulse-width
|-
| 12
| Horizontal Image Size (mm)
|-
| 13
| Vertical Image Size (mm)
|-
| 14
| Horizontal Image Size / Vertical Image Size
|-
| 15
| Horizontal Border
|-
| 16
| Vertical Border
|-
| 17
| Type Of Display
|}
'''Type Of Display:'''
{| class="wikitable"
|-
! Bit(s)
! Description
|-
| 7
| Interlaced
|-
| 5-6
| Stereo Mode (00 - No Stereo, 01 - Right Stereo Sync High, 10 - Left Stereo Sync High)
|-
| 4-3
| Sync Type (00 - Analog Composite, 01 - Bipolar Analog Composite, 10 - Digital Composite, 11 - Digital Separate)
|-
| 2
| Serrate (OR Vertical Sync Polarity IF 'Sync Type' == 11)
|-
| 1
| Sync Location (OR Horizontal Sync Polarity IF 'Sync Type' == 11)
|-
| 0
| Unused?
|}
== Get preferred resolution ==
<syntaxhighlight lang="c">
void get_preferred_resolution(uint8_t *edid, int *x, int *y) {
*x = edid[0x38] | ((int) (edid[0x3A] & 0xF0) << 4);
*y = edid[0x3B] | ((int) (edid[0x3D] & 0xF0) << 4);
}
</syntaxhighlight>
== See Also ==
=== External Links ===
* [http://www.edidreader.com/ Online parser for EDID information]
* [https://web.archive.org/web/20080614205229/http://www.vesa.org/public/VBE/VBEDDC11.PDF VBE/DDC 1.1 Specification]
* [https://glenwing.github.io/docs/VESA-EEDID-A2.pdf VESA EDID 1.4 Specification]
[[Category:Video]]
[[Category:Hardware Detection]]
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