Nearly all modern PC graphics cards use the same 15 pin conenctor that the original IBM VGA card used. VGA=Video Graphics Adapter or Video Graphics Array. Videotype: Analogue.
15 pin HIGHDENSITY D-SUB FEMALE connector at the videocard
|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|
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 1024x768GND means connected to ground
n/c means that the pin has not connected anywhere
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 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 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 ID3When grpahics card detects data on data-line it starts to read the data coming from the monitor syncronous 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 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)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.
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).