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U2520D, P2317H, DP MST daisy chain not working
Hello Dell Community!
I just bought a 2nd Dell monitor (U2520D) and I'm trying to DP MST daisy chain it the following way:
Inspiron 5000 Laptop Intel HD Graphics 620 USB Type-C out port --> U2520D USB Type-C to C cable --> U2520D USB Type-C in port
U2520D DP out port --> U2520D DP to DP cable --> P2317H DP in port
The U2520D works fine but after many hours of troubleshooting.I still did not manage to get the P2317H to work. The error shown on the P2317H is "The current input timing is not supported by the monitor display". I tried to change the resolution down to 1920x1080 and 60Hz (for the U2520D) as per the error message, but the P2317H still does not show anything.
I even tried this the same configuration with a Lenovo T480, but the same error occurs. I would be so grateful if someone could enlighten me as to what I may have done wrong.
Many thanks in advance!
Jermyn
jphughan
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August 23rd, 2020 08:00
@JHiddenStar Go into the U2520D's onscreen menu, select Display, and set USB-C Prioritization to "High Resolution" rather than "High Data Speed". Your system supports DisplayPort 1.2/HBR2, which means that if you want to run QHD+FHD (aka 1440p+1080p), you need the first display to set up the USB-C link to maximize video bandwidth. The tradeoff to that is that your USB data speeds will be limited to USB 2.0. When a USB-C link is set up to carry both video and USB 3.x, carrying USB 3.x cuts available video bandwidth in half, and with a DisplayPort 1.2/HBR2 system, a half bandwidth link isn't enough to run QHD+FHD. If you want to maintain USB 3.x data speeds based on the type of peripherals you've got connected to your U2520D, then you'll have to connect the P2317H to your system some other way so that its bandwidth requirements don't have to be met by the USB-C output.
Dropping the resolution on the U2520D to 1080p would normally have freed up enough bandwidth to work around what I just described, but a) running a QHD display at FHD isn't a great idea, since it will look blurrier than an actual FHD display of the same size would, and you'll have wasted money going QHD, and b) depending on how you changed the resolution, you might have just changed the "desktop resolution" that Windows renders at, while the "active signal resolution" might have stayed at QHD. That would NOT have freed up any bandwidth. There are reasons for keeping the active signal resolution at the display's native resolution even if you want your desktop to be rendered at a lower resolution, but that's a longer discussion.
jphughan
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14K Posts
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August 24th, 2020 06:00
@JHiddenStar Happy to help! Although I'm actually surprised that worked because the U2520D manual specifically says that when MST (daisy chaining) is enabled -- which it would've been in your case since you were already able to use the P2317H in extend mode -- then the USB-C Prioritization option is set to High Resolution by default. So I thought that your display might already have been set that way and therefore the problem would be something else. Did your display default to High Data Speed, or did you change that setting yourself at some point not knowing what the ramifications were? In any case, glad you're set!
JHiddenStar
6 Posts
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August 24th, 2020 06:00
@jphughan Thank you so much! That totally solved my problem! Thanks for the technical explanation, I would never have figured this out on my own