OWC TB2 Dock, dual displays, Daisy chained DP displays

Discussion in 'MacBook Pro' started by crankerchick, Mar 14, 2018.

  1. crankerchick macrumors newbie

    crankerchick

    Joined:
    Oct 18, 2013
    #1
    i have a mid 2014 15” MBP and the thunderbolt 2 dock. I just purchased a Dell U3415W (3440x1440) to replace my existing Dell P2414H (1920x1080). I decided to try to use both displays through the dock and read in the manual for the dock that 2 displays can only be used if both use the native connection. What does that mean, to be native? I took it to mean no adapters, so I connected the U3415W via HDMI and the P2414H via DP-mDP but it still didn’t work. Only 1 display worked at a time.

    I’ve done some reading here and it seems you just can’t do dual displays with 1 dock, although it would be nice to understand why the manual says it’s possible. Does anyone know the answer to this?

    In my quest not to have to connect another cable to my laptop, I tried daisy chaining the 2 displays since the U3415W has DP out. I had the U3415W connected to the dock via mDP-DP and the P2414H to the U3415W via DP-DP. The P2414H would not sense the connection, not even when I removed the dock from the chain and connected the U3415W directly to the mbp. Any idea why this wouldn’t work? I did enable DP 1.2 in the menu settings of the U3415W.
     
  2. Anonymous Freak macrumors 603

    Anonymous Freak

    Joined:
    Dec 12, 2002
    Location:
    Cascadia
    #2
    Thunderbolt 2 Docks, almost without exception, only support one display, unless the second display is a Thunderbolt-native display. Even an iMac in Target Display Mode doesn't count, it has to be a full-native-Thunderbolt display like the Apple Thunderbolt Display. (Yes, I've tried everything I can think of.) It's a macOS limitation - apparently macOS can't send two separate video streams over one DisplayPort connection. And the Thunderbolt connection carries only one DisplayPort connection. So even daisy-chaining won't work, whether the first display is through a dock or direct to the Mac.

    Thunderbolt 3 docks don't seem to have this problem, but I don't know if it would apply through a Thunderbolt 3 to Thunderbolt 2 adapter or not.

    The only Thunderbolt 2 dock I've found that supports multiple displays in macOS that aren't Thunderbolt is from Startech, and both need to be native DisplayPort.
     
  3. crankerchick thread starter macrumors newbie

    crankerchick

    Joined:
    Oct 18, 2013
    #3
    Thank you for the thorough explanation. So native in the case of the dock manual means native Thunderbolt. Wish they hadn’t left that one word out in the manual. I wouldn’t have wasted my time on that path.

    Looks like if I want 2 displays im back to plugging in 3 cables to my MBP instead of 2.

    This is my work computer and they will be upgrading me any day now so I’ll get the thunderbolt 3 dock to go with a new MBP so I’m glad to hear the TB3 dock doesn’t has a workaround. Of course I’ll need a bunch of USB-C adapters but maybe I’ll be officially down to just one cable.
     
  4. crankerchick thread starter macrumors newbie

    crankerchick

    Joined:
    Oct 18, 2013
    #4
    I just reread the manual for the dock and see that it does in fact say "native Thunderbolt" display. I guess I glanced over this tidbit thinking using the thunderbolt port is the same as using a Thunderbolt display. Now I know Thunderbolt and DisplayPort are not the same thing, they just share the same connector, at least for TB and TB2.
     
  5. UnlikelyLass macrumors newbie

    Joined:
    Mar 28, 2016
    #5
    I have a Belkin TB2 dock with two outgoing DisplayPort ports and i have two monitors happily connected to it.

    The basic issue: there are two video streams encoded in TB2 and each one needs a TB device/chip/whatever to decode it.

    MOST TB2 docks only decode one stream — it’s more expensive to decode both because you need more chips. What you can do, however, is stick another daisy-chainable TB2 device in and get two monitors that way:

    Mac -> TB2 dock (with a video port of some kind) -> a second TB2 device (like a disk drive) -> a second monitor via a Mini DisplayPort cable coming off the second TB2 port on the second device.

    I have successfully done this. You do NOT need the second monitor to be TB2, you just need 2 daisy-chainable TB devices, each of which can decode one video stream. The second monitor terminates your daisy chain, since it’s not thunderbolt.

    I always feel like I make a hash of explaining this.
     
  6. crankerchick thread starter macrumors newbie

    crankerchick

    Joined:
    Oct 18, 2013
    #6
    I understand what you are saying. I don't foresee having the need to add any other thunderbolt devices for work purposes but it's good to know that if I do, I'll be able to leverage the thunderbolt port on that device to get the second video stream.

    I guess the OWC TB3 device has the second chip in it.
     

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5 March 14, 2018