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Q: 3rd monitor on docking staton?



 
 
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  #1  
Old March 31st 18, 02:44 PM posted to alt.comp.hardware
x13
external usenet poster
 
Posts: 2
Default Q: 3rd monitor on docking staton?

Hi all.

I own a Kensington docking station model sd3500v.
It has 1x DVI and 1x HDMI and connect to my laptop via a USB 3.0 cable.

I use 2 identical AOC 22" monitors (each has a VGA and HDMI ports but I only use the HDMI). I use a HDMI-DVI converter on one of the monitors cable so I can use both ports on the DS.


My question is this: Since DS' DVI port is dual-link, I could theoretically split both links into 2 HMDI channels (*) and thereby connect a 3rd monitor. But would this work ???

(* using a gizmo like this: http://www.bilder.tragant.de/produkt...bae5731cfc.jpg)

To be clear, here is an illustration of what I mean... (view with proportional font)

Current :
=======

Monitor_A - HDMI_port - HDMI_cable - ---------------- - sd3500v (HDMI_port)
Monitor_B - HDMI_port - HDMI_cable - HDMI-DVI_adapter - sd3500v (DVI_port)


Desired :
=======

Note that Monitor_C would be identical to Monitor_A and Monitor_B.

Monitor_A - HDMI_port - HDMI_cable - --------------------- - sd3500v (HDMI_port)

Monitor_B - HDMI_port - HDMI_cable \ 2x_HDMI-DVI-D_splitter - sd3500v (DVI_port)
Monitor_C - HDMI_poort - HDMI_cable /

Anybody have an idea?

Thanks
x13
(please reply in thread)


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  #2  
Old March 31st 18, 07:42 PM posted to alt.comp.hardware
Paul[_26_]
external usenet poster
 
Posts: 634
Default Q: 3rd monitor on docking staton?

x13 wrote:
Hi all.

I own a Kensington docking station model sd3500v.
It has 1x DVI and 1x HDMI and connect to my laptop via a USB 3.0 cable.

I use 2 identical AOC 22" monitors (each has a VGA and HDMI ports but I only use the HDMI). I use a HDMI-DVI converter on one of the monitors cable so I can use both ports on the DS.


My question is this: Since DS' DVI port is dual-link, I could theoretically split both links into 2 HMDI channels (*) and thereby connect a 3rd monitor. But would this work ???

(* using a gizmo like this: http://www.bilder.tragant.de/produkt...bae5731cfc.jpg)

To be clear, here is an illustration of what I mean... (view with proportional font)

Current :
=======

Monitor_A - HDMI_port - HDMI_cable - ---------------- - sd3500v (HDMI_port)
Monitor_B - HDMI_port - HDMI_cable - HDMI-DVI_adapter - sd3500v (DVI_port)


Desired :
=======

Note that Monitor_C would be identical to Monitor_A and Monitor_B.

Monitor_A - HDMI_port - HDMI_cable - --------------------- - sd3500v (HDMI_port)

Monitor_B - HDMI_port - HDMI_cable \ 2x_HDMI-DVI-D_splitter - sd3500v (DVI_port)
Monitor_C - HDMI_poort - HDMI_cable /

Anybody have an idea?

Thanks
x13
(please reply in thread)


If you look up the DVI article on Wikipedia, it will tell you that a
single link DVI supports 1920x1200 @ 60Hz via CRTRB (Reduced Blanking).
In other words, with minimal front porch and back porch timing, that's
the maximum resolution you can squeeze out of a 165MHz single lane.

In the Kensington docking station case (which might be using DisplayLink DL-3900),
the DisplayLink site shows support for 2048x1152. If we do the math

2048x1152 is approximately equal to 1920x1200

This means, in reality, it's a single link device, no matter
what we might think by looking at the fully-filled connector.

https://support.displaylink.com/know...lution-support

DisplayPort HDMI DVI VGA
DL-3900 2560x1600 2048x1152 2048x1152 1920x1080

Dual link DVI is not supported by any of DisplayLink's ICs. ===

And that means, this cheesy thing is unlikely to work. There
are *multiple* reasons this won't work. The crossbar on a GPU
isn't (normally) intended to split a DVI dual-link in half,
simply because the EDID doesn't support more than one monitor
at a time.

https://www.newegg.ca/Product/Produc...9SIA9UP3HB7120

EDID -------------------- EDID of Display 1 (resolution info)
+ 2 lanes --------------------- video lane -----------
----+
^ | X--- EDID of Display 2
| +---------------- video lane -----------
|
+--- Does the crossbar here support lane splitting ???
I'm not aware of any standard specifying such a behavior.

You will notice that device, while cheap, has no documentation
or reviews. Visually, that's the same adapter cable you posted
as far as I know. I just can't see how this is standards compliant.
This is like some old Composite video adapter that used to
hook to the green gun on VGA connectors - people used to
buy those and just throw them in the garbage. Because nobody
could figure out what hardware supported such a wacky mode.
(It might have worked on an Apple computer, but using a second adapter.)
I don't see this new digital-era device, ending up anywhere
but in the landfill. If the article had review comments,
I'm sure we'd receive an earful.

At least check the reviews before buying one of those...

*******

Now, there *is* a technology that does work. Matrox makes it.

You are unlikely to buy one of these, because of the price.
This converts the scan pattern, to two or three scan patterns
on output.

This drives two displays in panorama mode, while the
computer or video output device, thinks it is driving just
one monitor. This is an *active* device. Note that, I can tell
you right away, this won't work on your Kensington dock, because
your dock port doesn't support a wide enough display mode to
drive one of these. I'm only showing you this adapter,
to show how you do this properly. This is "closer" to being
standards compliant. Matrox provides a web page, where you
enter display information, and it tells you whether the
device (or video card) can support that mode. But your Kensington
dock doesn't have a wide enough output mode, to use this
approach.

http://www.matrox.com/graphics/en/pr...go/digital_se/

This one looks *passive* to me, and in need of a special GPU
mode I cannot imagine any GPU supporting.

https://www.newegg.ca/Product/Produc...9SIA9UP3HB7120

*******

Kensington recommends adding an additional active adapter. It's
suggested near the bottom of the product page.

https://www.kensington.com/en/ae/449...ocking-station

Add more screens

You can hook up even more monitors using a multi-display adapter,
which is available separately. These connect into one of the
six USB ports and can be used with DVI or VGA monitors.

But this is the only Kensington accessory I could find, and it's not
perfect for you. There must be a better device we could
chain off your dock, than this.

https://www.kensington.com/en/ae/452...isplay-adapter

*******

I don't know what the best USB3 to HDMI device would be.

I like this site, only for the fact they list the display chip
in the Technical Specifications, so you can tell what you're
getting. For example, this one uses a Silicon Image IC, and
while the adapter has two HDMI outputs, only one of them
could be used to drive a 4K monitor. Both of the ports here
are likely to drive your AOC 22" at 1920x1080 @ 60Hz without
a problem.

https://www.startech.com/AV/USB-Vide...apter~USB32HD2

There are a ton of these things out there, and four or more chip
companies making chips. The display adapters use varying levels
of compression. Compression *can* cost computing cycles on
your CPU, and compression is undesirable. This is why the
USB3 generation is so exciting, as it allows the possibility
of lighter weight compression for these adapters. I think at
least one adapter is adaptive, and avoids compression at all
if the output resolution is low enough.

Your laptop could well eventually "run out of steam" if
running too many displays off USB3 ports. And it can be the
type of compression used, that determines this.

The old USB2 DisplayLink solutions, you couldn't send video
because the link really wasn't fast enough. With your USB3
dock this should no longer be a problem. But if you chain
enough displays off the laptop, eventually the CPU will be
hitting 100% while a video plays. And it all depends on the
compression design choices of the USB3 adapter/dock chips.

Best guess,
Paul
 




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