|
From Brad Parker (out among the flat cornfields of
Iowa)
This is the terminator that came
with an M-motion
adapter. I suspect that it would work equally well with
the ATi Gup or
any other auxiliary video card. Probably keeps the video
drive amps on
the unused card from going into oscillation.
The terminator requires three 75 ohm
1/4 watt resistors.
As 75 ohms can be difficult at times to find, rest easy in
knowing that
the originals have a 20% tolerance, so any 5% tolerance or
better resistor
with an impedance between 63 and 100 ohms should
work.
The resistors are wired in parallel
between each
color's drive pin and it's respective ground. In addition,
the terminator
keys the monitor ID to 0 by having a jumper between the 0
ID pin and digital
ground. (Monitor Presence Detect ID=0); which together
with
opens on Pins 4, 12, and 15 (MPDID 1, 2, and 3) ensures
that the system
thinks an 8512 or 8513 (640x480 analog color only) monitor
is attached.
Use a 15 pin male VGA
connector
and hood. The component values are as follows: R1-R3 75
ohm 20% 1/4 watt
resistor J1 Insulated 24 gauge single conductor wire
Connect
as follows:
Pin
Pin
1
----^v^v^v^v----
6
2
----^v^v^v^v----
7
3
----^v^v^v^v----
8
10
----------------
11 (shorted, in words)
Note the original unit has
[heat] shrink tubing on
the resistor leads - Not a bad idea. An alternate
technique would be
to just plug in any old monitor on the base video VGA
output. Of course
that takes up a bit of physical desktop.
Will The Real ATI GUP
Terminator Stand Up?
From Carlyle Smith
The resistors provide a simulated load to
the RGB signal
circuits, a condition apparently required by the
M-Motion Adapter. Brad
thinks that this terminator may also work to satisfy the
ATI GUP logic
requirements.
This, in fact, may not be so.
In stark contrast,
I checked the terminators supplied with the ATI
Graphics Ultra Pro
16-bit ISA and MCA versions, and they are identical.
They
are wired like this:
Pin
Pin
1
---------------- 6
2
---------------- 7
3
---------------- 8
10
--------------- 11
In
words, the system still thinks that an 8512/3 display is
attached, but
that the color signals are shorted to their respective
grounds. I have
no idea what the system or GUP logic decides about
this. Maybe the
75-ohm load terminator and the dead-shorted terminator
may be interchanged.
Maybe not. There is an easy way to find out.
QED.
Peter Fires Back
Hi ! To add another bit of info: The ELSA
XHR Gemini/2
858 card comes with the same 75-Ohms resistor terminator
that Brad described.
Luckily I have the Gemini manuals and this defines the
use of the terminator
as follows:
Usually the card is designed to work
as "2 cards
/ 2 screens" solution. Under e.g. AutoCAD the normal VGA
displays the texts
and help screens, while the Gemini only displays the
hi-res graphics using
a Fixed frequency monitor.
Assumed you have a multisync
monitor you could
attach this to the Gemini and plug the terminator to the
standard VGA.
The Gemini/2 has VGA Loop Through capability without
additional components,
while the other (ISA/EISA) Geminis require a VGA feature
connector cable
or the Gemini VGA loop through Add-On board (Rem: the
Gemini/2 uses the
AVE connector on the MCA). With the GMISETUP the
card must be configured
as VGA loop through / single screen installation. That's
all.
Personally I want to add that a *short circuit*
(Null Ohm) between
any of the RGB color signals and their according GND
returns is a bad idea.
I would not recommend to use a "plug" that shorts
the video card
outputs to GND with no resistor between. This could
cause damage of the
video output drivers ... and if that video card is a
planar-Video you will
probably need a new board afterwards.
XGA-2 Pinout (XGA/VGA
similar)
Pin Signal
1
Red
2
Green
or monochrome
3
Blue
4
Monitor
ID 2 (not connected)
5
Ground
6
Red
ground
7
Green
ground or monochrome ground
8
Blue
ground
9
Reserved
10
Ground
11
Monitor
ID 0 (not connected)
12
Monitor
ID 1 (not connected)
13
Horizontal
synchronization (Hsync)
14
Vertical
synchronization (Vsync)
15
Monitor
ID 3 (not connected)
|