Display Data Channel: Difference between revisions

Revision as of 05:12, 9 March 2024

Revision as of 05:15, 9 March 2024

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{{short description|Communication protocols}}

{{Cleanup bare URLs|date=August 2022}}

The '''Display Data Channel''', or '''DDC''', is a collection of [[Protocol (computing)|protocols]] for digital communication between a [[computer display]] and a [[Video card|graphics adapter]] that enable the display to communicate its supported [[display modes]] to the adapter and that enable the computer host to adjust monitor parameters, such as brightness and contrast.

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==Overview==

{{prose section|date=March 2024}}

The DDC suite of standards aims to provide [[Plug and Play]] and [[VESA DPMS|DPMS]] power management experiences for computer displays.

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Prior to the DDC, the [[VGA]] standard had reserved four pins in the analog [[VGA connector]], known as ID0, ID1, ID2 and ID3 (pins 11, 12, 4 and 15) for identification of monitor type. These ID pins, attached to resistors to pull one or more of them to ground (GND), allowed for the definition of the monitor type, with all open (n/c, not connected) meaning "no monitor".

In the most commonly documented scheme, the ID3 pin was unused and only the 3 remaining pins were defined. The ID0 was pulled to GND by color monitors, while the monochrome monitors pulled ID1 to GND. Finally, the ID2 pulled to GND signaled a monitor capable of 1024×768 resolution, such as [[IBM 8514]]. In this scheme, the input states of the ID pins would encode the monitor type as follows:<ref>{{Cite web|url=https://patents.google.com/patent/US5285197/en|title=Method and apparatus for automatic selection of scan rates for enhanced VGA-compatible monitors}}</ref><ref>[Monitor Pinouts http://www.cs.nyu.edu/~mwalfish/classes/15sp/ref/hardware/vgadoc/PINOUT.TXT Monitor Pinouts]</ref><ref>{{Cite web|url=https://pinoutguide.com/Video/VGA15_pinout.shtml|title=VGA pinout diagram @ pinoutguide.com|website=pinoutguide.com}}</ref>

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