Terminators for Enhanced video cards
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
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?
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
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:
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
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.