KB200: You want to know how EDID and DDC relate to your display resolution

Summary

Extended Display Identification Data (EDID), is a standard data format that contains basic information about a display device and its capabilities. The information is stored in the display device by the manufacturer and, when the device is connected to a PC, communicates its capabilities to a display adapter. The PC uses this information for configuration purposes so the monitor and system can work together.

EDID includes information such as:

  • manufacturer name
  • display device type and serial number
  • supported timings
  • display size and resolution
  • color characteristics
  • frequency range limits

EDID is what enables a PC to detect the type of monitor connected to it, enabling "plug and play" for your devices. EDID is transmitted from the device to your display adapter using a Dynamic Data Channel (DDC). DDC is a standard for communication between a monitor and a display adapter. The display adapter uses the EDID information to present you with valid options for configuring your display.

Both EDID and DDC have updated, enhanced versions (E-EDID and E-DDC) which extend the capabilities of the original standards.

Additional information

Display adapter drivers, DDC and Microsoft Windows

Typically, Microsoft Windows operating system drivers for display adapters access the EDID data in a display device to determine which resolutions are available for you to select in the Windows Display Properties dialog. Most current display adapter drivers properly support EDID and provide a list of resolutions based on this data.

Cables, connectors and DDC

It is important that all display device connections including cables (e.g. VGA, DVI or HDMI), splitters, amplifiers, repeaters and converters support DDC in order for the display device's EDID information to be available. When extending or splitting a signal it is important to test your hardware and cabling configuration in advance of deploying the configuration into production because some devices intended for splitting or extending a cable do not support DDC.

When working with display resolutions and DDC there are several possible problems that can affect the EDID data:

  • EDID/DDC are missing or corrupted. Long cable runs degrade the DDC signal. When your display devices send their EDID, it does not reach the display adapter without experiencing some level of data corruption.
  • EDID/DDC are unsupported by your hardware. Some VGA, DVI and HDMI hardware do not support DDC. Introducing devices that do not support DDC, in order to extend or split a cable, prevent the EDID data from reaching the display adapter.
  • Windows does not communicate with the display. Starting a computer when your display device is in standby mode disrupts the communication between the display device and the operating system and prevents the EDID from transmitting to the display adapter. This causes the display adapter driver to revert to Windows default resolutions.
  • Errors in display programming or documentation. Some display devices contain incorrect EDID data resulting in a display adapter driver attempting to drive the screen with incorrect settings. Your display device's user documentation is erroneous and you will not realize that your display device and display adapter will not communicate the EDID.

Typically, display adapters and devices support DDC and EDID.

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