[ranma42]

DisplayPort is the more surprising one. DDC came from VGA and DVI and uses the I2C lines that also connect the EDID EEPROM, but Displayport doesn't even have I2C pins if you look at the pinout, so it has to be tunneled: "DisplayPort does not have the I2C SLA/SLC pins. Instead, the logical I2C signals are converted at each end into messages on the AUX channel. Put another way, DDC is implemented using the AUX channel, but the AUX channel itself is not DDC. The "multiplexing" of I2C over the AUX channel is transparent to all but the lowest level of I2C software at each end."