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Kovacs

macrumors member
Original poster
Sep 27, 2007
37
0
Oslo, Norway
I apologize if this topic has been answered elsewhere, I have googled for hours now but have not found the solution.

I have a MacBook Pro 15" (late 2016) with 4 TB3 ports.

Today I received a new Dell U3421we ultrawide monitor. I thought it should be possible to drive this monitor with a single USB-C to USB-C cable. But I am getting a max resolution of 2560x1440 with USB-C.

With a USB-C to DP adapter I get 3440x1440 @ 60hz which is the correct resolution for this monitor.

Is there no way to get this via USB-C only? One major reason for me to get this monitor was single-cable connection and 90W charging over USB-C.
 

Kovacs

macrumors member
Original poster
Sep 27, 2007
37
0
Oslo, Norway
Answering myself. The answer was to switch the USB-C priority on the monitor from "High data speed" to "High resolution". That solved it instantly.
 

joevt

Contributor
Jun 21, 2012
6,625
4,063
Answering myself. The answer was to switch the USB-C priority on the monitor from "High data speed" to "High resolution". That solved it instantly.
Right. USB-C DisplayPort Alt Mode has two connection types:

1) four lanes of DisplayPort + USB 2.0 (high resolution)
2) two lanes of DisplayPort + USB 3.x (high data speed)

because there are only four SuperSpeed lines in a USB-C cable. USB 3.x uses two of the lines, one for transmit and one for receive, leaving only 2 lines for DisplayPort lanes (transmit only)

If you want high resolution and high data speed, then you need to use one cable for USB and another cable for DisplayPort - or use a Thunderbolt 2 or Thunderbolt 3 display or dock.

High resolution and high data speed is possible using USB-C instead of Thunderbolt, but only if DSC is supported and used (as in the CalDigit SOHO USB-C dock or in some new displays) or you use 4:2:0 chroma subsampling. The GPU of the 2016 MacBook Pro doesn't support DSC (DSC is a smarter compression format than 4:2:0). DisplayPort 1.2 supports 4:2:2 but not 4:2:0. Apple broke (or purposefully disabled) DSC in Big Sur.
 

Kovacs

macrumors member
Original poster
Sep 27, 2007
37
0
Oslo, Norway
Thank you for an informative answer! I will be getting a new M1 MacBook Pro at work in a few months. Will the new computer be able to drive the monitor at high resolution and high data speed?

I must say that the U3421we is amazing. It replaced a u2515h which I have been very happy with, so I chose this exact monitor because I wanted the same quality but in a larger screen. I am very happy with it so far. It is the most expensive monitor I have ever bought.

And I used the occasion to get rid of one of my external drives and moved everything on it into iCloud.
 

joevt

Contributor
Jun 21, 2012
6,625
4,063
Thank you for an informative answer! I will be getting a new M1 MacBook Pro at work in a few months. Will the new computer be able to drive the monitor at high resolution and high data speed?
Reread what I wrote. The only way to get both high resolution and high data speed with that monitor is to use two cables to the monitor - one for USB (USB Type B or USB Type C) and one for DisplayPort (DisplayPort or USB Type C) - data and video both can't come from USB-Type C unless you exclude either high resolution or high data speed.

According to the manual, it doesn't appear that you can use USB type B upstream when using USB Type C DisplayPort input unless you're using PIP/PBP mode. I wonder if you can work around that by using a bi-directional USB-C to DisplayPort cable connected to the USB-C upstream port of the display - in that case, there's no USB input on the USB-C upstream port so maybe the display will automatically switch USB input to USB Type B upstream.

If you want a single cable to the display, and high resolution and high data speed, then you can use a single cable to a Thunderbolt dock and then two cables from the dock to the display.

The M1 MacBook Pro supports DSC, so a USB-C dock like the CalDigit SOHO which has an internal DisplayPort 1.4 MST Hub that supports DSC and can decompress DSC to a display that doesn't support DSC (like the U3421we) could work if Apple didn't break DSC in Big Sur. DSC is required to provide high resolution through USB-C (not Thunderbolt) when it is also doing USB 3.x high data speed.
 

macrumorsnumpty

macrumors member
Jan 26, 2018
53
17
France
I apologize if this topic has been answered elsewhere, I have googled for hours now but have not found the solution.

I have a MacBook Pro 15" (late 2016) with 4 TB3 ports.

Today I received a new Dell U3421we ultrawide monitor. I thought it should be possible to drive this monitor with a single USB-C to USB-C cable. But I am getting a max resolution of 2560x1440 with USB-C.

With a USB-C to DP adapter I get 3440x1440 @ 60hz which is the correct resolution for this monitor.

Is there no way to get this via USB-C only? One major reason for me to get this monitor was single-cable connection and 90W charging over USB-C.
How are you finding the U3421WE?

I had colour uniformity issues with my first one. I initially put it down to my error, then checked and changed the cables, then checked and changed the machine and laptops, GPU, operating systems (windows and mac), did calibrations, the whole shebang. Nothing changed the colour problem. I just put it down to bad luck. So I returned it, the replacement was just as bad. x5 monitors later, all with varying issues of colour uniformity, I gave up.

I loved the monitor, just not my colour issues.

What does yours look like on a grey screen with brightness at 38?
 

5425642

Cancelled
Jan 19, 2019
983
553
Reread what I wrote. The only way to get both high resolution and high data speed with that monitor is to use two cables to the monitor - one for USB (USB Type B or USB Type C) and one for DisplayPort (DisplayPort or USB Type C) - data and video both can't come from USB-Type C unless you exclude either high resolution or high data speed.

According to the manual, it doesn't appear that you can use USB type B upstream when using USB Type C DisplayPort input unless you're using PIP/PBP mode. I wonder if you can work around that by using a bi-directional USB-C to DisplayPort cable connected to the USB-C upstream port of the display - in that case, there's no USB input on the USB-C upstream port so maybe the display will automatically switch USB input to USB Type B upstream.

If you want a single cable to the display, and high resolution and high data speed, then you can use a single cable to a Thunderbolt dock and then two cables from the dock to the display.

The M1 MacBook Pro supports DSC, so a USB-C dock like the CalDigit SOHO which has an internal DisplayPort 1.4 MST Hub that supports DSC and can decompress DSC to a display that doesn't support DSC (like the U3421we) could work if Apple didn't break DSC in Big Sur. DSC is required to provide high resolution through USB-C (not Thunderbolt) when it is also doing USB 3.x high data speed.
So what your saying is that it's now way you can connect two cables to the display without being limited of the data speed if you want the high resolution?

I was thinking of something like this; Connect USB-C and then also connect the USB
Super speed USB 5Gbps (USB 3.2 Gen1) Type-B Upstream port to my MacBook Pro m1

I was hoping to get High res and High data speed
 

joevt

Contributor
Jun 21, 2012
6,625
4,063
So what your saying is that it's now way you can connect two cables to the display without being limited of the data speed if you want the high resolution?
I said connecting two cables is the only way to get full data and resolution.

I was thinking of something like this; Connect USB-C and then also connect the USB
Super speed USB 5Gbps (USB 3.2 Gen1) Type-B Upstream port to my MacBook Pro m1
I said, according to the manual, it doesn't appear that you can use type B upstream when using USB Type C DisplayPort input unless you're using PIP/PBP mode. Maybe the manual is wrong. Or maybe you can try my idea of using USB-C without USB - by using a bi-directional USB-C to DisplayPort cable connected to the USB-C upstream port of the display (use a USB-C to DisplayPort adapter if your computer has a USB-C output connected to the DisplayPort end of the USB-C to DisplayPort bi-directional cable).
 

5425642

Cancelled
Jan 19, 2019
983
553
I said connecting two cables is the only way to get full data and resolution.


I said, according to the manual, it doesn't appear that you can use type B upstream when using USB Type C DisplayPort input unless you're using PIP/PBP mode. Maybe the manual is wrong. Or maybe you can try my idea of using USB-C without USB - by using a bi-directional USB-C to DisplayPort cable connected to the USB-C upstream port of the display (use a USB-C to DisplayPort adapter if your computer has a USB-C output connected to the DisplayPort end of the USB-C to DisplayPort bi-directional cable).
Sorry I don’t understand how you mean?
I have two USB-C on my MacBook m1.
Should I connect one to the “default” usb-c on the display with charging etc and the other usb-c on my MacBook i put a USB-C to DP adapter and then connect the DP cable to the display?
 

joevt

Contributor
Jun 21, 2012
6,625
4,063
Sorry I don’t understand how you mean?
I have two USB-C on my MacBook m1.
Should I connect one to the “default” usb-c on the display with charging etc and the other usb-c on my MacBook i put a USB-C to DP adapter and then connect the DP cable to the display?
Yes, that's one way to get full speed data and video.
 

5425642

Cancelled
Jan 19, 2019
983
553
How are you finding the U3421WE?

I had colour uniformity issues with my first one. I initially put it down to my error, then checked and changed the cables, then checked and changed the machine and laptops, GPU, operating systems (windows and mac), did calibrations, the whole shebang. Nothing changed the colour problem. I just put it down to bad luck. So I returned it, the replacement was just as bad. x5 monitors later, all with varying issues of colour uniformity, I gave up.

I loved the monitor, just not my colour issues.

What does yours look like on a grey screen with brightness at 38?
You must have bad luck I also have the display and it works great! I can measure if it's any Uniformity during the weekend. But I don't think it is I can't see it anyway I'll also calibrate it during the weekend. I can get back with the report.
 

5425642

Cancelled
Jan 19, 2019
983
553
How are you finding the U3421WE?

I had colour uniformity issues with my first one. I initially put it down to my error, then checked and changed the cables, then checked and changed the machine and laptops, GPU, operating systems (windows and mac), did calibrations, the whole shebang. Nothing changed the colour problem. I just put it down to bad luck. So I returned it, the replacement was just as bad. x5 monitors later, all with varying issues of colour uniformity, I gave up.

I loved the monitor, just not my colour issues.

What does yours look like on a grey screen with brightness at 38?
Here is the file everything looks good at my display.

Can't see anything with the naked eye.
 
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