EDID

Extended Display IDentification 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 VBE.)

Reading EDID

The first step is, naturally, to actually get the data. This is done through the BIOS - int 0x10, ax=4F15h, bl=01h.

mov ax, 0x4f15
mov bl, 0x01
mov cx, 0
mov dx, 0
int 0x10
;AL = 0x4F if function supported
;AH = status (0 is success, 1 is fail)
;ES:DI contains the EDID

Note that this code will only run in Real Mode or Virtual 8086 Mode.

EDID Data

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EDID record:

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)