Prev: Free wheeling mouse with THUNK technology?
Next: Monitor will not turn on. Does it have a fuse I can change?
From: Matthew on 4 Aug 2010 08:00
I have 2 computers hooked up to one monitor via a KVM, both of which are
running nVidia cards with the latest drivers. If I power on both systems at
once, the computer that is not currently "live" on the KVM will
automaticallly kick down to the lowest screen resolution. I understand why,
but is there a way to force it to always use a certain resolution so I'm not
constantly having to reset it? And more importantly... is there a way to do
it without turning each computer on individually as I'm sure someone will
suggest :)


From: Paul on 4 Aug 2010 10:09
Matthew wrote:
> I have 2 computers hooked up to one monitor via a KVM, both of which are
> running nVidia cards with the latest drivers. If I power on both systems at
> once, the computer that is not currently "live" on the KVM will
> automaticallly kick down to the lowest screen resolution. I understand why,
> but is there a way to force it to always use a certain resolution so I'm not
> constantly having to reset it? And more importantly... is there a way to do
> it without turning each computer on individually as I'm sure someone will
> suggest :)
>
>

See the "Compatibility" section here, for why this happens.

http://en.wikipedia.org/wiki/KVM_switch

A modern KVM that supports electronic switching, should be
able to "fool" the disconnected computer, into thinking it is
still driving a monitor. The two functions needing support are:

1) Constant impedance, to prevent Hot Plug Detect events.
And if failing to do that without glitching ...

2) A copy of the EDID contained in the monitor, should be available
to any PC at any time. That means effectively, the KVM copies
the table from the monitor, into an internal storage device,
and reads it out to any PC asking for it.

It would have been easy to support more than one video card
reading the EDID, except for some statements here.

http://en.wikipedia.org/wiki/Display_Data_Channel

"Though I2C is fully bidirectional and supports multiple bus-masters,
DDC2B is unidirectional and allows only one bus master - the graphics
adapter."

That probably simplifies the design of the GPU on the video card a tiny bit.

I interpret that to mean, you cannot create a "party line" and allow
all the PCs on the KVM, to share the same DDC channel to the monitor
at the same time. And that makes the requirements on the KVM, a bit
more difficult to meet. It means the monitor DDC could be connected to
the "current" PC, but then, what do the other PCs do in the interim ?

They do make individual, inline connected EDID boxes, for feeding
a computer a fake EDID table. Typically, they're used in situations
where the display device doesn't have its own EDID table. But for the
price of one of these per computer, you'd be better off buying a
good KVM instead.

"Kramer VA-1VGA"

http://www.kramerelectronics.com/products/model.asp?pid=730&f=34668

To use one of those, you'd connect a surrogate to the EDID capture
box, and copy the EDID table into the box. Then, when a "dumb" display,
lacking EDID, is connected, the EDID capture box answers the query, in
place of the dumb device. EDID capture boxes are typically used with
VGA connected wall projectors, as the projector doesn't typically have
an EDID. But for the price of one of those, one per PC connected to the
KVM, you could probably buy a new KVM for less. (As far as I know, there
are also DVI versions available as well. DDC is used on both VGA and DVI.)

So if the problem was that the computer wasn't able to read the
EDID, when it starts up, one of those boxes would fix it, for that
computer. You'd need a box per computer, to keep them all happy,
at perhaps $85 per box. (The fact it's a box, with two connectors, and
a power supply, is why the price has to be so high. If the function
was integrated into the KVM itself, the impact on the end user price
would be a lot less.)

PC --- EDID_Box ---+
\___ KVM ____ Monitor
/
PC --- EDID_Box ---+

As far as I know, both ATI and Nvidia cards would work the same way,
with respect to DDC display channel on the video connector.

HTH,
Paul
 | 
Pages: 1
Prev: Free wheeling mouse with THUNK technology?
Next: Monitor will not turn on. Does it have a fuse I can change?