Q: What is VESA DDC 2?

Filed under FAQ / Electrical

Answer:

DDC2 allows bidirectional communication: monitor can tell its parameters and the computer can adjust monitor settings. The bidirectional data bus is a synchronous data bus similar to Access Bus and is based on I2C technology. The following pins on VGA pinout have to be changed to enable DDC2 to work:

       VGA pin    new function
        9     Optional +5V output from graphics card
	12     Bidirectional data line (SDA)
	15     Data clock (SLC)
        

The signals in the data bus are standard I2C signals. The computer provides 15 kohm pullup for the SDA and SLC lines. Monitor must provide 47 kohm pull-up on SCLK line.