There are at least four versions of the VGA connector, which are the three-row 15 pin DE-15 (also called mini sub D15) in original and DDC2 pinouts, a less featureful and far less common 9-pin VGA, and a Mini-VGA used for laptops. The image and below table are the newer 15-pin VGA VESA DDC2 connector pinout.
|1||RED||Red Video (75 ohm, 0.7 V p-p)|
|2||GREEN||Green Video (75 ohm, 0.7 V p-p)|
|3||BLUE||Blue Video (75 ohm, 0.7 V p-p)|
|4||ID2||Monitor ID Bit 2|
|9||KEY||-||Key (No pin)|
|11||ID0||Monitor ID Bit 0|
|12||ID1 or SDA||Monitor ID Bit 1|
|13||HSYNC or CSYNC||Horizontal Sync (or Composite Sync)|
|15||ID3 or SCL||Monitor ID Bit 3|
VGA pinout : monitor ID detection pin assignments
4 11 12 ID2 ID0 ID1 n/c n/c n/c no monitor n/c n/c GND Mono monitor which does not support 1024x768 n/c GND n/c Color monitor which does not support 1024x768 GND GND n/c Color monitor which supports 1024x768
GND means connected to ground
n/c means that the pin is not connected anywhere
This monitor type detection is becoming more and more obsolete nowadays. New VGA plug-and-play monitors communicate with the computer according to VESA DDC standard.
VESA Display Data Channel is a method for integrating digital interface to VGA connector so as to enable the monitor and graphics card to communicate. There are two different levels of DDC: DDC1 and DDC2.
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!).
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 (SCL)
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.