[geeks] Not all cables are created equal (DVI)

[Charles Shannon Hendrix]

On Tue, 24 Oct 2006 11:23:19 -0400
"Francois Dion" <francois.dion at gmail.com> wrote:

> Just wanted to mention, if you buy an LCD monitor and you run
> >1280x1024 at 60hz and you notice that you can run at that resolution
> with the analog (vga) input but cannot run anything higher than
> 1280x1024 in digital mode, you are a victim of a cheap manufacturer.
> 
> Viz, I got a Samsung SyncMaster 204B, very happy with it, does
> 1600x1200. It came with a DVI cable, strange because Samsung doesn't
> ship one according to their web site. 

My Samsung 204B came with a VGA cable and a single-link DVI cable, both
of which work fine.  I got mine from Best Buy, and it says on the box
that it comes with cables.

> This however was bought from Dell (dont ask), so I'm assuming they
> added their own cable. 

That's weird.

...and I have to ask, sorry:

Just curious, how much did you pay?

I got mine for $356 including tax.

> I just replaced my ATI with a Quadro FX 550 (you need an Nvidia
> card to get accelerated OpenGL in Solaris x86/x64) which has 2 DVI
> ports. So I used the cable that shipped with the monitor to connect
> to the video card, but it kept forcing 1280x1024, stating the monitor
> couldn't do higher, which is not true.

That sounds like a driver issue to me.  Either that, or the card has
buggy cable detection.

You don't need dual-link for the 204B.

> In the meantime I had already ordered a longer DVI cable, because the
> bundled cable was too short. I was regretting having put more money
> into something that wouldn't work for me. Well, upon receiving the new
> cable, the issue became obvious. The cable that shipped with the
> monitor is a "single link" while the new cable (I asked for a 15ft
> DVI-D capable of 1600x1200) is a "dual link" (see the illustration at
> http://en.wikipedia.org/wiki/DVI ).

Single-link is used from 21-165MHz.  It doesn't matter what your cable
quality level is, this is an absolute cap.  That's equivalent to about
3.7Gbits/sec.

With dual-link, the hardware tests the cable to determine the maximum
speed, thus it is limited only by cable quality.

A 1440 display should not need it either, as it has less pixels than
1600x1200.

It's odd that replacing the cable fixed things, because you don't need
dual-link.

Sounds like a driver issue or the card wanted dual-link for some reason.

> Yet the Quadro FX sense reports that the 6ft long single link cable
> couldn't get to UXGA resolution (for example). The 15ft long dual link
> had no problem, but it is supposed to be capable of (according to
> wikipedia again):
> 
> HDTV (1920 W 1080) @ 85 Hz with GTF blanking (2W126 MHz)
> WQXGA (2560 W 1600)@ 60 Hz with GTF blanking (2x174 MHz) (30" LCD
> Dell, Apple, Samsung)
> 
> However the DVI-D dual link I received ("QVS digital dvi premium
> cable") only supports 1600x1200.

I never ran a Quadro but it sounds like it is messing up, or the driver
is.

What OS are you using and what driver?

How many pin blocks does your cable have?

A single link is a pair of 9 wire blocks.  Dual link is a is a single
block of 24 pins.

On both there is also a blade pin offset from the blocks.


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shannon "AT" widomaker.com -- ["Castles are sacked in war, Chieftains
are scattered far, Truth is a fixed star, Eileen aroon!" -- Gerald
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