25 Jan
2007
25 Jan
'07
6:28 p.m.
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
Isn't pin 4 strictly a self-test pin, designed to make an unplugged
monitor give some illumination on the screen?
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
It might well be just that (well, 75 Ohm resistors would be the
'stnadard'). I konw some VGA cards sensed the load resistance on the RGB
lines to determine if they were driving a monochrome (only loaded the 'G'
line iIRC) or a colour monitor.
My suggesition is 'try it'. I can't do any damage, and it might well work.
-tony