VGA (15) 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 sopport 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 conenctor to be able the monitor and grapahics card to communicate. There are two different levels of DDC: DDC1 and DDC2.

DDC1

DDC1 allows the monitor to tell it"s parapeters to the computer. The following VGA card connector pins had to be changed to allow DDC1 fuctions:

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

DDC2

DDC2 allows bidirectional communication: monitor can tell it"s parameters and computer can adjust monitor settings. The bidirectional data bus is a syncronous data bus similar to Access Bus and is based on I2C technology. Tho following pins had to be changed to to enable DDC2 to work:

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

NOTE: If the optional +5V power output pin is used, a special DDC/VGA connector must be used to to provide proper sequencing. The +5V output voltage must be withing +/-5% range and tha card must be able to supply at least 300 mA current (maximum 1A).