VGA connector

Pin	Name	Dir	Description
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
5	GND		Ground
6	RGND		Red Ground
7	GGND		Green Ground
8	BGND		Blue Ground
9	KEY	-	Key (No pin)
10	SGND		Sync Ground
11	ID0		Monitor ID Bit 0
12	ID1 or SDA		Monitor ID Bit 1
13	HSYNC or CSYNC		Horizontal Sync (or Composite Sync)
14	VSYNC		Vertical Sync
15	ID3 or SCL		Monitor ID Bit 3

Note: Direction is Computer relative Monitor. All signals except R, G, B are TTL level signals.

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

This monitor type detection is becoming more and more obsolete nowadays. New plug-and-play monitors communicate with the computer according to VESA DDC standard.

VESA DDC

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

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

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 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

DDC2 allows bidirectional communication: monitor can tell it’s 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 have to be changed to enable DDC2 to work:

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