Display Data Channel

The Display Data Channel or DDC is a digital connection between a computer display and a graphics adapter that allows the display to communicate its specifications to the adapter. The standard was created by VESA.

Mechanical

The DDC link is carried on three pins - data, clock and ground - in either a 15-pin VGA connector or a DVI connector.

Electrical

The current version of DDC, called DDC2B, is based on the I²C bus defined long ago by Philips. This is a serial bus that allows multiple bus masters, although DDC2B allows only one master - the graphics adapter. The monitor (e.g. a CRT or LCD) contains a read-only memory (ROM) chip programmed by the manufacturer with information about the graphics modes that the monitor can display.

Logical

The data in the monitor's ROM is held in a standard format called EDID (for Extended Display Information Data). This format is defined the Video Electronics Standards Association (VESA).

References

• Extended Display Identification Data (EDID) Standard, Version 3, 1997, VESA