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Should this "Thunderbolt" cable setup work? Maybe I need some 101 on this topic...
Posted by: SKYLANE
Date: February 25, 2021 01:51AM
I am not up to speed yet on the nuances of specs regarding Thunderbolt cables (and perhaps the latest USB specs). My experience with Thunderbolt is still limited, feel free to help me out on any details that I might be missing out on. Focus of this thread is on the cable/adapter setups shown in BLUE below. The MacBook Air is currently on Big Sur 11.2.1, the setup below has even worked on previous macOS's prior to Big Sur.



I have used this setup shown here for some time now, and it works very well. I even drive a Dell Monitor with a DP cable hooked up to the LaCie 2BIG (which is a TB3 Dock with internal 8TB hard drive storage):

MacBook Air 7,2 >>> Apple Thunderbolt 2 Cable >>> Apple Thunderbolt 2 Adapter to Thunderbolt 3 (USB-C) >>> LaCie 2BIG



In an effort to replicate the above setup for a similar setup I have, I substituted a Tripp Lite cable I found at Office Depot into the above setup to test it (specs: [assets.tripplite.com] ):

MacBook Air 7,2 >>> (Display Port side) Tripp Lite U444-006-MDP (USB-C side) >>> LaCie 2BIG

I selected this Tripp Lite cable to save some money over buying another Apple cable & adapter.



I am trying to figure out why the Tripp Lite U444-006-MDP cable does not work at all in this setup when substituting it for the Apple cable & adapter. No function at all. Should I expect the Tripp Lite cable to work, or am I missing some detail in the specs that would tell me that it can't do what I desire in the setup shown above? (BTW, I tried a second Tripp Lite Cable of the same part number, that did not work either.)



Edited 9 time(s). Last edit at 02/25/2021 03:59AM by SKYLANE.
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Re: Should this "Thunderbolt" cable setup work? Maybe I need some 101 on this topic...
Posted by: Sarcany
Date: February 25, 2021 05:43AM
Quote
SKYLANE
I selected this Tripp Lite cable to save some money over buying another Apple cable & adapter.

You have a USB-C to Mini Displayport cable. It is just a dumb display cable. It doesn't carry a Thunderbolt signal or any type of signal other than video for a display.

Thunderbolt 2 on the Mac uses a Mini Displayport form-factor and Thunderbolt cables plug into the Mini Displayport port. But the port has multiple functions. It can be used to connect Thunderbolt devices, and it can be used to connect BOTH Thunderbolt devices and a display (daisy-chained) and it can be used without Thunderbolt at all just to connect a display.

To use Thunderbolt on a Mac with Mini Displayport ports requires cables/adapters that support Thunderbolt in that form-factor. Your Tripp Lite cable does not support Thunderbolt. It's just a dumb display cable. It won't pass a Thunderbolt signal.

Thunderbolt on newer Macs -- and on some devices like a Thunderbolt-3 LaCie drive -- passes its signal over a USB-C connection instead of Mini Displayport. As with the Mini Displayport port on your old Mac, the USB-C form-factor is used, but you need a USB-C Thunderbolt cable in order to use Thunderbolt on a new Mac. If you use a dumb USB-C display cable on a new Mac, you can only use it to connect a display. If you use a USB-C data-cable on a new Mac, you can only use it to connect USB devices.

Your Tripp Lite cable was designed to work as a display-only cable for USB-C ports. It passes a display signal from a USB-C Mac or PC to a display that has a Mini Displayport input. It does not pass a Thunderbolt signal. It would not work to pass any other sort of signal than video.

It only works in one direction. That is, it won't even work to connect a Mini Displayport Mac to a USB-C display. It only works to connect a USB-C Mac or PC to pass a video signal to a display.

So, your original solution, connecting a Thunderbolt cable to your old MacBook Air and then a Thunderbolt/USB-C adapter to connect to the LaCie drive is the right one.



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Re: Should this "Thunderbolt" cable setup work? Maybe I need some 101 on this topic...
Posted by: space-time
Date: February 25, 2021 06:17AM
So they mixed the Thunderbolt protocol, the USB-C protocol, the DisplayPort protocol, with miniDisplay port and USB-C ports and you can get almost any combination of cables and ports and it's not clear what will work and what not. Always choose the most capable cable if you think you may need to change the setup in the future.
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Re: Should this "Thunderbolt" cable setup work? Maybe I need some 101 on this topic...
Posted by: bazookaman
Date: February 25, 2021 06:47AM
What is it they say? USB-C is a connector. Thunderbolt is a protocol. So you need a true Thunderbolt cable. Hence the increased cost. Real deal Thunderbolt cables have the lighting bolt on them.







Edited 1 time(s). Last edit at 02/25/2021 06:47AM by bazookaman.
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Re: Should this "Thunderbolt" cable setup work? Maybe I need some 101 on this topic...
Posted by: SKYLANE
Date: February 25, 2021 03:15PM
Quote
Sarcany
Your Tripp Lite cable was designed to work as a display-only cable for USB-C ports. It passes a display signal from a USB-C Mac or PC to a display that has a Mini Displayport input. It does not pass a Thunderbolt signal. It would not work to pass any other sort of signal than video.

It only works in one direction. That is, it won't even work to connect a Mini Displayport Mac to a USB-C display. It only works to connect a USB-C Mac or PC to pass a video signal to a display.

I was wondering if this wasn't the case after all of my fiddling around with that cable. Thanks for explaining that all to me.



Quote
Sarcany
So, your original solution, connecting a Thunderbolt cable to your old MacBook Air and then a Thunderbolt/USB-C adapter to connect to the LaCie drive is the right one.

I did order another Apple cable & adapter for the second computer setup, which solved everything.

Hopefully, if I take these Tripp Lite cables (I had bought two of them) back to Office Depot they will be able to refund my purchase or give me Store Credit. If not, they will show up in the "For Sale & Free Items" section of our forum.



Thanks to all of you for inputs. Good information to be found here, as always!




Edited 1 time(s). Last edit at 02/25/2021 03:17PM by SKYLANE.
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