Display Data Channel: Difference between revisions

Revision as of 22:29, 1 March 2024

Revision as of 05:08, 9 March 2024

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=== DDC2 {{anchor|DDC2B}} ===

The most common version, called '''DDC2B''', is based on [[I²C]], a [[Serial communications|serial bus]]. Pin 12, ID1, of the VGA connector is used as the data pin of the I²C bus, and the formerly-unused pin 15 is the I²C clock. Pin 9, previously used as a mechanical key, supplies +5V DC power (up to 50mA) to power the EEPROM. With this, the host can read the EDID even if the monitor is powered off. Though I²C is fully [[Two-way communication|bidirectional]] and supports multiple [[Bus mastering|bus-masters]], DDC2B is unidirectional and allows only one [[Bus mastering|bus master]] -- the—the graphics adapter. The monitor acts as a slave device at the 7-bit I²C address 50h, and provides 128-256 bytes of read-only EDID. Because this access is always a read, the first I²C octet will always be A1h.

{{anchor|DDC2Ab}}

'''DDC2Ab''' is an implementation of the I²C-based 100-kbit/s [[ACCESS.bus]] interface, which made it possible for monitor manufacturers to support external ACCESS.bus peripherals such as a mouse or keyboard with little to no additional effort. Such devices and monitors were briefly available in the mid -1990s, but they disappeared with the introduction of [[Universal Serial Bus|USB]].

'''DDC2B+''' and '''DDC2Bi''' are scaled-down versions of DDC2Ab which only support monitor and graphics card devices but still allow bidirectional communication between them.

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** [http://www.ddc-ci.com/ softMCCS]: Windows software which uses DDC/CI to control monitors supporting this protocol

** ''[http://www.nicomsoft.com/wini2cddc/ Nicomsoft WinI2C/DDC]: Windows Software Development Kit (SDK) which uses I2C and DDC/CI protocols to control monitors'' (removed from support, downloadable ZIP files don't contain application)

** [https://github.com/emoacht/Monitorian Monitorian]: Open source application that uses DDC/CI to change brightness from aan icon in the Task Bar

** [https://github.com/xanderfrangos/twinkle-tray Twinkle Tray]: similar to Monitorian

** [https://github.com/blackholeearth/Win10_BrightnessSlider Win10_BrightnessSlider]: similar to Monitorian