U4021QW, MST daisy chain support?

Question

Hello,

I bought the Dell UltraSharp U4021QW monitor and am very happy with it. The picture is amazingly sharp and enormously colorful, and the factory calibration is excellent! The only complaint is that the monitor could be a bit brighter.

The main issue/my question:

I would like to connect a second monitor in series using the MST (Multi-Stream Transport) standard. Unfortunately, I can't find any information anywhere about whether the unit supports this function? However, I would be very surprised if this device did not support MST.

I would like to realize the following setup:

Connect my Dell XPS 13 7390 via Thunderbolt 3 to the U4021QW monitor and additionally plug my older Dell U2410 via DP daisy chain to the U4021QW.

I have not found any activation options for DP: neither in the Intel graphics settings nor on the U4021QW or U2410.

Furthermore, I reduced the resolutions on the U4021QW and U2410 to 1280*720 (60Hz or 30Hz) to ensure no bandwidth problems. I also connected the U2410 via HDMI to the U4021QW, but in no case did I get a picture, nor was the U2410 visible in the Windows settings.

Have I done something wrong? Can anyone confirm if the U4021QW supports MST at all?

Thank you very much for your help.

jphughan · Accepted Answer

@jamesbender Daisy chaining requires a DisplayPort output. The U4021QW only has a DisplayPort input. And I suspect the reason it doesn’t offer daisy is due to its own bandwidth requirements, its requirement for DisplayPort 1.4 just to run itself rather than the still much more common DP 1.2, and the fact that it uses Thunderbolt 3. I haven’t seen a display that uses TB3 also offer a regular DisplayPort MST output. Some TB3 displays have a downstream TB3 port to create a Thunderbolt daisy chain, but in that case the second display must also be Thunderbolt. I realize you took steps to reduce bandwidth requirements, but many customers would likely not know to do that or would not consider that an acceptable solution.

Also, it’s not clear from your post whether you have a regular XPS 13 7390 or an XPS 13 7390 2-in-1. Only the latter supports DP 1.4, so if you have the former, you might not be able to run that display at its native resolution and refresh rate. TB3 has enough total bandwidth, but that’s because with DP 1.2 it carries two independent interfaces, but I don’t think that Intel GPU can aggregate those to run a single display. In that case you’d only be able to use a single DP 1.2 interface to run the display, leaving the other unused, and that isn’t enough for 5120x2160 60 Hz. With DP 1.4, a single interface is enough to run that setup.

DELL-Chris M · Answer

The U4021QW does not have the required video OUT port to facilitate the MST daisy chain to another monitor. All of its video ports (HDMI 1/HDMI 2/DP/TB3-DP) are IN only.

This is why neither the online U4021QW User's Guide nor the U4021QW Menu OSD mention MST daisy chain.

Each monitor will need to connect to the XPS 13 7390. One way to set this up would be =

* Plug the external AC power adapter into the XPS 13 7390 primary left side TB3/USB Type-C port
* XPS 13 7390 secondary left side TB3/USB Type-C port --> U4021QW USB Type-C to C cable --> U4021QW TB3-DP in port
* XPS 13 7390 right side USB Type-C port --> USB Type-C to DisplayPort cable --> U2410 DP in port

Monitors

U4021QW, MST daisy chain support?

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