Using the 23.7-inch LG UltraFine 4K Display over USB-C

Aiwi

macrumors member
Original poster
Oct 21, 2010
39
24
The previous 21" 4K Ultrafine was connected to your computer using the USB standard. According to the following support document over at Apple, the new 24" monitor not only has Thunderbolt 3 but also USB as display input.

Has anyone been able to confirm this? I am curious whether I can connect it to my RTX GPU using the GPU USB-C connector and a USB-C-USB-C cable. On the previous Ultrafine 4K 21" this is fully possible. Albeit not really useful in macOS just yet due to the lack of drivers.

System requirements and compatible Mac models
The LG UltraFine 4K Display requires a Mac with a USB-C port or Thunderbolt 3 (USB-C) port running macOS Mojave 10.14.5 or later, or an iPad Pro with a USB-C port.

You can use the LG UltraFine 4K Display at the following resolutions and refresh rates, depending on your device:

3840 x 2160 @ 60Hz

iMac Pro
Learn how to connect multiple displays to your iMac Pro
iMac introduced in 2017 or later
Mac mini introduced in 2018
Learn how to connect multiple displays to your Mac mini (2018)
MacBook Pro introduced in 2016 or later
MacBook Air introduced in 2018
MacBook introduced in 2016 or later
iPad Pro with USB-C
Mac computers with Thunderbolt 2 ports using the Thunderbolt 3 to Thunderbolt 2 adapter
3840 x 2160 @ 48Hz

MacBook introduced in 2015
Learn how to adjust your display’s resolution.
https://support.apple.com/en-ng/HT210105
 

chrfr

macrumors G3
Jul 11, 2009
9,722
3,582
The previous 21" 4K Ultrafine was connected to your computer using the USB standard. According to the following support document over at Apple, the new 24" monitor not only has Thunderbolt 3 but also USB as display input.

Has anyone been able to confirm this?
Why would Apple put out a technical document detailing the connections and compatibility and then lie about it?
 
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changguangyu

macrumors newbie
Sep 15, 2017
22
5
Yes. You can. USB c of RTX is VirtualLink standard, which is DP1.4 + USB 3.1 Gen2 + 27w power delivery.
 

joevt

macrumors 65816
Jun 21, 2012
1,428
693
Yes. You can. USB c of RTX is VirtualLink standard, which is DP1.4 + USB 3.1 Gen2 + 27w power delivery.
VirtualLink is a new USB-C alt mode.

The new LG display uses either DisplayPort alt mode (with USB 2.0) or Thunderbolt (which is basically another USB-C alt mode). Thankfully, the RTX cards also support DisplayPort alt mode. The new LG display is able to use USB-C or Thunderbolt because it uses the new Titan Ridge Thunderbolt 3 controller.

DisplayPort alt mode has a couple different versions:
- USB 3.1 gen 2 with two lanes of DisplayPort (allows 4K 30 Hz when using DisplayPort 1.2).
- USB 2.0 with four lanes of DisplayPort. I believe this is the mode used by the new LG display (like the older LG display) otherwise it wouldn't be able to support 4K 60Hz with older Macs.

VirtualLink is similar to the latter mode, but can transmit USB 3.1 gen 2 over the lines that are normally used for USB 2.0. This requires a new cable spec to beef up those lines.

The support page says 4K 60 Hz is supported by the MacBook (Retina, 12-inch, Early 2016) but the technical specifications say that that MacBook only supports 4K 30 Hz. Maybe the 10.14.5 version of Mojave (that the support page says is required) unlocks that resolution for the MacBook?

The support page does not mention computers that don't have Thunderbolt or USB-C ports. Does this mean the display can't work with a Moshi USB-C to DisplayPort Cable (it's supposed to be bi-directional)? If that's true, then these computers would require a DisplayPort to USB-C converter such as a Sunix UPD2018 or a Delock 89582 or a GC-ALPINE RIDGE or a GC-TITAN RIDGE.
 

ning_greennet

macrumors newbie
Jun 25, 2019
9
3
Vancouver
Yes, it does work with the Moshi cable, but I don't recommend to work in windows with 24 Ultrafine, reason?
1. you can't adjust the brightness in windows
2. The colour in windows looks weird to most people
3. You have to plug-unplug the cable each time you switch the inputs(between PC and macbook)
Overall, get a different monitor if your PC needs a 4K monitor.
 

joevt

macrumors 65816
Jun 21, 2012
1,428
693
Yes, it does work with the Moshi cable, but I don't recommend to work in windows with 24 Ultrafine, reason?
1. you can't adjust the brightness in windows
2. The colour in windows looks weird to most people
3. You have to plug-unplug the cable each time you switch the inputs(between PC and macbook)
Overall, get a different monitor if your PC needs a 4K monitor.
For brightness in windows, did you try an app that uses DDC/CI instead of USB?
If the display works with the Moshi cable, then it probably works with the Huawei VR 2 Computer Connection Cable DP1.2 + USB2.0 to Type-C Cable which will provide USB 2.0 which should solve at least the brightness problem.
 

ning_greennet

macrumors newbie
Jun 25, 2019
9
3
Vancouver
For brightness in windows, did you try an app that uses DDC/CI instead of USB?
If the display works with the Moshi cable, then it probably works with the Huawei VR 2 Computer Connection Cable DP1.2 + USB2.0 to Type-C Cable which will provide USB 2.0 which should solve at least the brightness problem.
Yes, I just tried an app with DDC/CI features. It does work to adjust the brightness of the Ultrafine. Thank you for the input. Now the major problem is the plug-unplug issue. Hope could get a new thunderbolt 3 hub 2 females to 1 male with a switch to turn on or off.
 

joevt

macrumors 65816
Jun 21, 2012
1,428
693
You have to plug-unplug the cable each time you switch the inputs(between PC and macbook)
I don't understand the problem with this. In what situation would you not need to plug-unplug a cable to switch a display between computers? Maybe you mean the monitor only has one display input where a better monitor would have more than one input that can be switched using a simple on screen control?

There exists a Thunderbolt 2 KVM switch that could work if both of your computers support Thunderbolt 2 or Thunderbolt 3. The MacBook doesn't support Thunderbolt though, so you'll probably have to use a USB-C KVM (unless you have a MacBook Pro or MacBook Air?). I don't know of any USB-C KVM's, so you might want to try a DisplayPort + USB KVM with two Huawei VR 2 Computer Connection Cable DP1.2 + USB2.0 to Type-C Cables.
 

ning_greennet

macrumors newbie
Jun 25, 2019
9
3
Vancouver
I don't understand the problem with this. In what situation would you not need to plug-unplug a cable to switch a display between computers? Maybe you mean the monitor only has one display input where a better monitor would have more than one input that can be switched using a simple on screen control?

There exists a Thunderbolt 2 KVM switch that could work if both of your computers support Thunderbolt 2 or Thunderbolt 3. The MacBook doesn't support Thunderbolt though, so you'll probably have to use a USB-C KVM (unless you have a MacBook Pro or MacBook Air?). I don't know of any USB-C KVM's, so you might want to try a DisplayPort + USB KVM with two Huawei VR 2 Computer Connection Cable DP1.2 + USB2.0 to Type-C Cables.
Hi Joevt, thank you for the prompt response, let me make it clear to you.

Now, I have a MacBook Air 2018 and a PC, and a 23.7 new Ultrafine. There are 2 usb-c ports on the Ultrafine for inputs. Both of the usb c ports work in a thunderbolt 3 mode or a USB-Type C Alternative mode. If I plug the usb c cable from the MacBook Air and the display port to usb c cable from the PC into the 2 usb c ports on my Ultrafine at the same time, none of them will work. I guess perhaps the software deems that the second plug-in cable as a daisy chain monitor.

However, if I unplug either one of them, the other one will work. That's why I want to have a thunderbolt 3 hub: 2 females usb c to 1 male usb c and a switch to decide which way the signal will go. The two usb-c cable go into the 2 females and the male end goes into the monitor. So I could switch to the PC or MacBook Air with the switch on the hub.

I want to do that because I don't think the ports on the Ultrafine will last long if I plug-unplug the cable in and out several times a day.
 

joevt

macrumors 65816
Jun 21, 2012
1,428
693
Hi Joevt, thank you for the prompt response, let me make it clear to you.

Now, I have a MacBook Air 2018 and a PC, and a 23.7 new Ultrafine. There are 2 usb-c ports on the Ultrafine for inputs. Both of the usb c ports work in a thunderbolt 3 mode or a USB-Type C Alternative mode. If I plug the usb c cable from the MacBook Air and the display port to usb c cable from the PC into the 2 usb c ports on my Ultrafine at the same time, none of them will work. I guess perhaps the software deems that the second plug-in cable as a daisy chain monitor.

However, if I unplug either one of them, the other one will work. That's why I want to have a thunderbolt 3 hub: 2 females usb c to 1 male usb c and a switch to decide which way the signal will go. The two usb-c cable go into the 2 females and the male end goes into the monitor. So I could switch to the PC or MacBook Air with the switch on the hub.

I want to do that because I don't think the ports on the Ultrafine will last long if I plug-unplug the cable in and out several times a day.
Ok, so the display can accept only one input and doesn't have an on screen control to switch inputs. Your only solution is probably a DisplayPort + USB KVM switch with two Huawei cables because there probably does not exist a USB-C switch that will work (especially one that will switch between DisplayPort alt mode 8.1 Gbps x4 simplex and Thunderbolt 3 20 Gbps x2 duplex).
 

ning_greennet

macrumors newbie
Jun 25, 2019
9
3
Vancouver
Ok, so the display can accept only one input and doesn't have an on screen control to switch inputs. Your only solution is probably a DisplayPort + USB KVM switch with two Huawei cables because there probably does not exist a USB-C switch that will work (especially one that will switch between DisplayPort alt mode 8.1 Gbps x4 simplex and Thunderbolt 3 20 Gbps x2 duplex).
Thank you again Joevt for the reply, the setting is a bit too complicated for me or too expensive. I hope somebody could come up with a product like this since I guess many people want to connect the UltraFine for multiple devices. Or if LG could develop a software in LG screen Manager for switching devices, that could much better. Although I don't think they will do that since they sell Ultrafine only for Apple product.
 
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LiE_

macrumors 6502a
Mar 23, 2013
733
1,253
UK
I see rumours of Navi having USB-C like RTX. This could mean in the future we see native Navi support via eGPU on the LG Ultrafine 23.7 monitor.
 
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