Display Data Channel
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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.
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[edit] Mechanical
The DDC link is carried on three pins – data, clock and ground – in a 15-pin VGA connector, a DVI connector or an HDMI connector.
[edit] Electrical
The current version of DDC, called DDC2B, is based on the I²C bus. 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.
[edit] 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 by the Video Electronics Standards Association (VESA).
[edit] Enhanced Display Data Channel (E-DDC)
This version incorporated VESA DDC version 3 standard. Major changes were the addition of the E-DDC protocols, removal of DDC1 protocol and clarification to the DDC power requirements.
In Version 1 Revision 1, scope has been expanded to encompass usage in consumer electronic products and video interfaces other than VGA with text clarified in several places. Support for the P&D and FPDI-2 standards has been eliminated.
[edit] DDC/CI
DDC/CI (CI = command interface) is an extension to DDC specified by VESA in August 1998. It allows a computer with a suitably designed graphics adapter to adjust monitor parameters such as brightness and colour balance, or to initiate degaussing. DDC/CI monitors are sometimes supplied with an external colour sensor, to allow automatic calibration of the monitor's colour balance. Some tilting DDC/CI monitors support an auto pivot function, where a rotation sensor in the monitor enables the operating system to keep the display upright as the monitor is moved between its portrait and landscape positions.
The latest version of the specification is "Display Data Channel Command Interface (DDC/CI) Standard- Version 1.1", October 2004 (VESA document VESA-2004-10).
Specific command used to control monitors are defined in Monitor Control Command Set (MCCS) Standard.
[edit] References
- Extended Display Identification Data (EDID) Standard, Version 3, 1997, VESA
- VESA Standards FAQ
