On Thu, 25 Jan 2007, Jules Richardson wrote:
Some of you here might know this :) I've got a
system here where I need
to make it think that there's a monitor plugged into its VGA port even
when there isn't (long story).
Plugging a real CRT into the port even when that CRT is switched off and
unplugged from the AC supply works, so there's obviously some way of
doing it.
Measuring the CRT above (switched off, unplugged from AC, and unplugged
from the device) with respect to the VGA connector's shield gives me the
following readings:
pin sig value
1 R 76ohm
2 G 76ohm
3 B 76ohm
4 NC GND
5 GND GND
6 GND GND
7 GND GND
8 GND GND
9 NC infinite resistance
10 GND GND
11 NC GND
12 DDC DAT 8.1Kohm (initially 7.6Kohm, rose at first then steadied)
13 HSYNC 4.6Kohm
14 VSYNC 4.7Kohm
15 DDC CLK 8.1Kohm (initially 7.6Kohm, rose at first then steadied)
Any suggestions? Do I just need 76ohm resistors to
ground on the RGB lines
(and possibly 4.7Kohm resistors to ground on HSYNC and VSYNC)? Or is there
likely something more subtle going on that I need to incorporate into my
"fake" connector? (Given that VGA supplies no DC out, it can't be anything
too complex!)
Pins 11, 12, 4, 15 are the monitor id pins 0-3. Pin 5 is the monitor's
digital ground pin, 6, 7, 8 are the RGB grounds, respectively, and 10 is
the sync ground.
Its been years since I did this sort of thing, but I believe I jumpered
one or more of the id pins to ground to get mine to work. I might have
used a resistor, but I don't remember now.
Newer monitors and VGA cards use one of the pins for digital communication
with the monitor, but I don't remember the specifics.
-Toth