Display Data Channel: Difference between revisions

Revision as of 23:13, 22 February 2022

Revision as of 09:18, 25 March 2022

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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>[https://www.google.com/patents/US5285197 Patent US5285197 &ndash; Method and apparatus for automatic selection of scan rates for enhanced VGA-compatible monitors]</ref><ref>http://www.cs.nyu.edu/~mwalfish/classes/15sp/ref/hardware/vgadoc/PINOUT.TXT {{Bare URL plain text|date=March 2022}}</ref><ref>http://pinouts.ru/Video/VGA15_pinout.shtml</ref>

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