USB 3.0 downgraded to USB 2.0 using some hubs/devices

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USB 3.0 downgraded to USB 2.0 using some hubs/devices

Hi,

I am connecting my 2017 MacBook Pro to a new LG 32UD99-W display using the supplied USB-C cable. The video runs fine, but when I connect my USB 3.0 WD Passport external HDD, system information reports the HDD, as well as the LG USB hub as 2.0 (with max speed of 480Mb/s). If I connect the HDD using a little USB 3.0-to-USB-C ADATA dongle (or rather a stick adapter), it does the same thing - the WD appears as USB 2.0.

However, if I use other dongles (Satechi, PowerCord), I see the WD as 3.0 and it physically transfer files at about double the speed.

I am suspecting my Mac not to be able to communicate with some USB-C-to-USB-3.0 devices. Any idea why this is happening?

Running Catalina.

MacBook Pro 13", macOS 10.15

Posted on Jan 31, 2020 1:19 AM

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Answer 1

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dwb

Level 7

33,310 points

Jan 31, 2020 7:05 AM in response to Ondrej210

USB 3 cables and USB 2 cables are not wired the same. There are USB 2 hubs and USB 3 hubs - the name speaks for itself. USB 3 devices can be plugged into USB 2 hubs and connected with USB 2 cables but doing so will result in a USB 2 connection speed. Your description is a little sparse and disconnected (mixing your LG TV with dongles) but I suspect that 1) the display either has a USB 2 port or 2) the cable is a USB 2 cable.

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Answer 2

Ondrej210 Author

Level 1

9 points

Feb 2, 2020 6:27 AM in response to Ondrej210

UPDATE:

Apparently, there is an explanation for this behavior and I found a mention here:

https://9to5mac.com/2016/06/04/lg-27ud88-w-usb-c-4k-monitor-macbook-review/

and here:

https://forums.macrumors.com/threads/4k-at-60hz-on-12-rmb-hack-monitors-cables-adapters-that-work.1974167/

It says that:

"USB-C has four high-bandwidth lanes that can be dedicated to either USB 3.1 Gen 1 (i.e. USB 3.0 - 5Gbps) or DisplayPort 1.2. In addition to these four lanes, USB-C has separate USB 2.0 and power lanes that are available at all times. Running 4K at 60Hz requires the bandwidth of all four lanes, which would limit USB to 2.0..."

OK, fine, but why wasn't I warned about this behavior at the product page?

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Answer 3

dwb

Level 7

33,310 points

Jan 31, 2020 11:03 AM in response to Ondrej210

contact LG support?

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Answer 4

Ondrej210 Author

Level 1

9 points

Jan 31, 2020 10:53 AM in response to dwb

Thanks for your reply but no, all devices that I am dealing with are USB 3.x. The monitor is connected via a USB-C cable to my MacBook Pro. The USB-C cable is supposed to carry: 1) power delivery to the laptop, 2) video via the alternate DP mode, and 3) USB 3.1 data to/from the built-in USB 3.0 hub. 1) and 2) works fine. But for 3) - I am seeing the built-in hub (as well as anything USB 3 connected to it) as USB 2.

There are no USB 2 cables nor any USB 2 devices involved.

Any suggestions? Thanks

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Answer 5

Ondrej210 Author

Level 1

9 points

Jan 31, 2020 11:41 AM in response to dwb

I did, but nothing reasonable from them. The other part of the story is that I tried to connect my USB3 WD Passport HDD to my MacBook Pro via a convertor (USB-C to USB 3.0) and it's doing the same thing. However with two USB-C multi-function dongles (both have ethernet connector, card reader, HDMI, and USB 3.0 ports), the WD Passport is recognized correctly as USB 3.0.

To sum up:

LG monitor USB hub and USB-C adapter downgrade to USB 2.0, however, Satechi and PowerCord dongles do not downgrade.

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USB 3.0 downgraded to USB 2.0 using some hubs/devices

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