Q: What is VESA DDC 1?

Filed under FAQ / Electrical

Answer:

DDC1 allows the monitor to tell its parameters to the computer. The following VGA card connector pins have to be changed to allow DDC1 functions:

       VGA pin    new function
        9     Optional +5V output from graphics card
	12     Data from display
	14     Standard vertical sync signal which works also as data clock
	15     Monitor ID3
        

When the VGA graphics card detects data on data-line it starts to read the data coming from the monitor synchronous to vertical sync pulse. Vertical sync pulse frequency can be increased up to 25 KHz for the time of the data transfer if a DDC1 compliant monitor is found (be sure not to send those high frequencies to non DDC1 monitors!).

Related links

• VGA Timing