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Tech Talk: Using USB-C and DisplayPort over Alt Mode

Continuing our discussion on display technologies, let’s turn our attention to USB-C and DisplayPort. The DisplayPort protocol, which used to have a unique connector, is now transferred by way of the USB-C connector. The Type-C connector delivers DisplayPort technology via an Alternative Mode (Alt Mode).

With USB-C you get:

Even though USB-C is capable of supporting all of these features, not all of them are present all the time. Users will need to know the specifications of their devices to understand the display protocols supported.

What is Alt Mode?

Alt Mode is a term you will come across frequently when investigating USB-C.

Alt Mode is a functional extension of USB-C which enables the USB connection to carry non-USB signals. Alt Mode(s) are optional capabilities that are unique to the USB-C connector or port that allow technologies, like DisplayPort and Thunderbolt 3, to be transmitted. Knowing what devices and ports support the various Alt Modes may be confusing and, at times, frustrating.

DisplayPort over Alt Mode

DisplayPort Alt Mode (DP Alt Mode) allows a USB-C equipped computer to connect directly to a display or monitor. The monitor will need to have a USB-C port for you to make this connection. You can still use a USB-C equipped laptop with monitors that have more traditional video ports, such as VGA, DVI, HDMI, and DisplayPort but you will need to get a USB-C video adapter.

What do I need to know before using DisplayPort over Alt Mode?

  • Confirm your computer’s USB-C port supports DP Alt Mode
  • Read the tech specs on the USB-C video adapter to ensure it supports the resolutions and refresh rates you want
  • If you are interested in a USB-C MST video adapter or laptop docking station, make sure your video card also supports MST

Our next and final display technology post will offer tips for using Thunderbolt 3 and MST.

Catch up on Display Technology 101 and tips and tricks for using MST and DisplayPort.

Stay tuned!

11 Comments

  1. Horst Wischnat 9 months ago

    How to check •whether my computer’s USB-C port supports DP Alt Mode

    • Susan Mutterback 9 months ago

      Hi Horst,
      Thanks for reading this post! The best place to find this information is your laptop’s manual or website.

  2. anilroy 6 months ago

    thanks for information of usb-c it is quite interesting for me to learn the new technology and their generations

  3. Paulus 5 months ago

    Thanks for this, it is nice to know someone else understands this. Indeed it is frustrating dealing with parts suppliers to confim the adaptors actually work!

    I have a Zenfone 3 deluxe that supposed to support USB-C Alt Mode, but I am having a terrible time getting a port replicator. I ended up just buying a Miracast dongle instead, and casting the phone to the monitor, then using usb-c for charging, keyboard and mouse, but still I want a docking station.

    Hopefully more adaptors and port replicators will come out, and the people selling them will actually know if they work or not!

  4. Mathieu 3 months ago

    I have a portable usb-c screen with DP alt mode compatibility, I connect it for now to mij mini gaming rig that only has USB-C 3.1, will there ever be an adapter that connects from my desktop DP and usb to an USB-C DP alt connection?

    • Barry Weston 2 months ago

      Hello Mathieu,

      It sounds like you are trying to find a solution that would require USB-C with DP-Alt mode on your host device. Unfortunately, that is not technically possible.

      Thanks,

      Barry

  5. Carson 2 months ago

    I got a Dell U3818DW monitor, it does have a USB-C port which supports DP Alt Mode. And I got a Pixel 2 XL phone.

    But why, the monitor still not able to display anything after connecting them with a USB-C cable.

    • Barry Weston 2 months ago

      Hi Carson,

      Unfortunately, the Pixel 2 XL does not support video out over the USB-C port. At this time, there are no products we could recommend to connect your Pixel 2 XL directly to a display.

      Thanks.

      • Carson 1 month ago

        Oh I see…so that means I must use a USB-C to HDMI or Display Port converter in order to transfer display signal to a compatible monitor right?

  6. Christopher 1 month ago

    I know the Asus B9440UA-XS74 supports video out over the USBC3.1 ports, as it comes with an adapter to add a single HDMI output, and has an optional docking station for up to two connections from 2xDP,1xHDMI,1xVGA. Does this imply that I would be able to use your 3 HDMI MST hub for my 3 monitors from this ultrabook, given that the Intel® HD Graphics 620 is supposed to support up to 3 displays? Asus is not particularly helpful with specification (the page on their site loads blank) or customer service inquiries (taking sometimes weeks to get a non-answer). Thank you.

    • Barry Weston 1 month ago

      Hi Christopher,

      The answer to your questions isn’t a simple yes or no.

      The first thing to consider is the maximum number of displays your Intel HD 620 graphics card supports. Intel graphics cards only support a maximum of 3 total displays. This includes the display of your laptop. Therefore, to use 3 external displays you will be required to disable your laptop display via display settings.

      Second, you will need to find out if the Asus (ultrabook and docking station) supports full DisplayPort 1.2. If it does, use of MST accessories, such as our MSTDP123HD will work. WIthout DisplayPort 1.2 support, the MST hub will not function correctly.

      Hopefully, that helps. Let us know if you need anything else.

      You can also speak with one of our Technical Advisors by phone or live chat. They can be reached here: StarTech.Support

      Barry

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