The most common version, called '''DDC2B''', is based on [[I²C]], a [[Serial communications|serial bus]]. Pin 12, ID1, of the VGA connector is now used as the data pin fromof the I²C bus, and the formerly-unused pin 15 becameis the I²C clock;. pinPin 9, previously used as a mechanical key, suppliedsupplies +5V DC power (up to 50mA) to drivepower the EEPROM,. With this allows, the host tocan 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 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 allowedmade it possible for monitor manufacturers to support external ACCESS.bus peripherals such as a mouse or keyboard with little to no additional effort;. suchSuch 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.
DDC2 is not exclusive to the VGA connector,interface. as bothBoth [[Digital Visual Interface|DVI]] and [[High-Definition Multimedia Interface|HDMI]] connectors feature dedicated DDC2B wires.
