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February 16th, 2021 20:00
U2720Q , "High Data Speed" vs "High Resolution"
Hi All,
I recently purchased a U2720Q monitor to use on my Apple Mac mini M1 (2020) running Big Sur 11.2.1. The monitor is connected to the Mac with the type C to type C cable that came in the box. However I have question about the 2 modes mentioned in the subject. Below are my findings so far using each mode. I would like to know if it is a limitation on the Mac mini or the monitor itself? Can I have HDR enabled with USB 3.0 speed? As you may know the USB ports available on the new Mac mini is very limited. This will save me from buying those expensive thunderbolt hubs.
"High Data Seed" mode:
- Display running at 3840x2160, 60Hz 30-bit
- USB ports running at USB 3.0
- No "HDR" selection in MacOS' Displays setting page
"High Resolution" mode:
- Display running at 3840x2160, 60Hz 24-bit
- USB ports running at USB 2.0
- "HDR" can be enabled in MacOS' Displays setting page
Any suggestions will be greatly appreciated. Thanks!
- Joe
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jphughan
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February 16th, 2021 21:00
@mach2joe If those are your findings, then I think that answers the question. But as general background info, the way USB-C works (prior to USB4, which this display doesn't support) is that it has 4 high speed lanes. Each lane can be allocated to video or USB 3.x data (or Thunderbolt, but that isn't relevant here). A full DisplayPort interface requires 4 lanes. Running USB 3.x data requires 2 lanes, which means that if you want to run video and USB 3.x together, your video bandwidth gets cut in half. USB 2.0 flows over pins dedicated to that purpose within the USB-C connector.
When you select High Data Speed, the connection is configured to support 2 lanes of DisplayPort and 2 lanes for USB 3.x. High Resolution causes the display to set up the connection for 4 lanes of DisplayPort and USB 2.0 (using those dedicated pins). The M1 Mac Mini supports DisplayPort 1.4/HBR3 over USB-C. Half of a DP 1.4 interface is enough for 4K 60 Hz, but apparently not 4K 60 Hz HDR. Limiting your USB speeds to 2.0 frees up more bandwidth, which is apparently needed for HDR. If you had a system that only supported DisplayPort 1.2/HBR2 over USB-C, this option is even more important because in that case you have to run High Resolution even to get 4K 60 Hz, otherwise you'd be limited to 4K 30 Hz if you wanted USB 3.x. This setting also comes into play on QHD/1440p displays where when you have a DP 1.2 system, you can choose to have QHD 60 Hz plus USB 3.x or dual QHD 60 Hz (via daisy chaining) with USB 2.0. But macOS doesn't support DisplayPort daisy chaining.
jphughan
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February 16th, 2021 22:00
@mach2joe A few minutes after I wrote that, I remembered that I have an Anker multi-purpose adapter (this one) that supports HDMI 2.0 output, and even though it's not mentioned in the specs, I have successfully run 4K 60 Hz HDR to my TV, while also running USB 3.x simultaneously. I was using a ThinkPad X1 Extreme Gen 2, which also supports DP 1.4/HBR3. That's the current standard until DisplayPort 2.0 arrives.
So in this case I'm not sure where the limitation lies here. One possible explanation is that my system and adapter might support DisplayPort DSC (Display Stream Compression), which would allow running setups that would not otherwise be possible -- but I'm not sure that's true as I have no way to gain visibility into that. Another possibility is that this could be an early lifecycle glitch on the M1 Mac Mini. It's had some (though impressively few given the nature of the shift), including one around ultrawide resolution displays. And a third possibility is that this is another interoperability issue between a Dell display and an Apple system. There have been a variety of those discussed here and on Apple's forums. It's not clear whose "fault" those are since both pieces of equipment work as expected when paired with other hardware, and Dell and Apple both seem to refer respective customers to each other for assistance.
But buying a Thunderbolt cable definitely won't solve anything since the display isn't a native Thunderbolt display. If it were, you would certainly have enough bandwidth for 4K 60 Hz HDR and USB 3.x simultaneously, but the display doesn't support it.
Incidentally, is your Mac Mini treating that display as a standard or Retina display? Apple defines "standard" displays as 100-110 ppi, and Retina as 200-220 ppi when it comes to desktops and laptops, but a 27" 4K display results in a density of 163 ppi, which is basically right between the two categories that Apple designs for. So it would seem to be an awkward fit either way, with items either being too small if it's treated as a standard display, or too large if it's treated as a Retina display. Apple's own displays only run 4K on 23" panels (iMacs) and if you go up to 27", the resolution has jumped to 5K.
Daniel Digi
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March 9th, 2022 06:00
I had the same issue and have resolved it.
Switch to High Data Speed and Turn Off Always On USB Charging.
I needed to connect my Logitech Brio 4K and it is possible only with USB 3.0.
The monitor is 4K so the picture is the same whenever I use High Data Speed or High Resolution Mode so you don't lose anything.
If you had a 5K or higher monitor then would be an issue.
Good luck.