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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!

27 Comments

  1. Horst Wischnat 1 year ago

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

    • Susan Mutterback 1 year ago

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

  2. anilroy 12 months ago

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

  3. Paulus 11 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 9 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 8 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 8 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 8 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 7 months 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 7 months 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 7 months 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

  7. Gabriel 6 months ago

    Hi Guys,
    One question. My monitor has an USB-C input, but my notebook doesn’t. I bought an adapter USB-C to VGA to be able to use it, but it didn’t work.
    Do these adapters need to always have the output source as being USB-C?

    • Andrea McDonald 6 months ago

      Hey Gabriel, in order to drive a USB-C display your notebook needs to be USB-C enabled as well. Let us know if you have any further questions.

  8. Mak 5 months ago

    Hi,

    Just to want make sure that if a USB C to DisplayPort ADAPTER works for a laptop, will a USB C to DisplayPort CABLE that supports Altmode also work for the same laptop? My question is, does it need to be a USB C video adapter as mentioned in the article to work or will a cable also work?

    • Elyse Trevail 5 months ago

      Hi Mak, if your laptop supports DP-Alt mode, then any USB-C to DP adapter or cable will work.
      If you are looking for a cable solution rather than an adapter check out this product. If you have any further questions, feel free to contact our Tech Support Team via Live Chat or Phone @ 1 800 265 1844. Thanks!

  9. jay 5 months ago

    Do you make a pci-e card that outputs DP alt mode over USB-C, so that video out over DP can be added to a desktop? This is for a SuperMicro server with old Matrox g200ew graphics that won’t take a second video card and is incompatible with DisplayLink. Thank you

    • startech
      startech 5 months ago

      Hey Jay, our USB-C cards won’t help with that, you would need a graphics card. I encourage you to contact our Tech Support Team directly at 1 800 265 1844 or via Live Chat. Thanks!

  10. Kate 5 months ago

    Hi, I would really appreciate your help. I spend many hours trying to find the answear but still have doubts. I’ve got dell 7710 with thunderbolt 3 and need usb c Alt Mode to be able to use cintiq graphic tablet I am hoping to buy. Would you say thunderbolt 3 can work as usb c alt mode?

    • Elyse Trevail 5 months ago

      Hi Kate, thanks for contacting us. By the sounds of it, you have done a lot of research already and we would agree with you that this should work, however, to be 100% sure we recommend you either contact Dell or the tablet maker directly to ensure your tablet will work as desired. Good luck!

  11. John 3 months ago

    USB-C MST is hard to find information about the internet, USB-C MST brings up product descriptions and MST is too generic. I’d recommend either linking to another article about MST or spell out the Acronym so people can research it on their own. With DP over USB-C apt mode, what does the graphical rendering? Is it simply pulling the display output from my graphics card giving me the same performance as if I plugged into the display output natively or is it coming from somewhere else, presumably with significantly less performance?

    • Danielle Mayea 2 months ago

      Hi John,

      MST stands for Multi-Stream Transport. Graphics cards that support MST allow rendering multiple independent displays over a single video port. In those cases, the graphics card itself is rendering the displays. When it comes to USB-C and Thunderbolt 3 however, the displays connected to these ports are rendered by the USB-C/Thunderbolt 3 chipset, in most cases. For performance information on using MST over USB-C or Thunderbolt 3 we recommend contacting the computer manufacturer.

      Thanks for your question!
      Danielle

  12. Drake 2 months ago

    I have an HP Elite lapdock that worked great with my Galaxy S9 via a Thunderbolt 3 USB-C cable, but when I try using my Razer Phone with it, only the keyboard works. No video signal goes out. I have read about users on the internet that were able to use the HP Elite lapdock with their Razer Phones, but it doesn’t work with mine. I even rolled back to Android 7.1.1 which is what the phone shipped with, and it still doesn’t work.

    • Danielle Mayea 2 months ago

      Hi Drake,

      We recommend contacting Razer for troubleshooting the video output feature on your phone.

      Thanks!
      Danielle

  13. John 2 months ago

    Does DP-Alt Mode work with usb-c/thunderbolt 3 ports? If not, is there an adapter?

    • Danielle Mayea 2 months ago

      Hi John,

      Thanks for checking out this article! Whether a USB-C port supports DP-Alt mode depends on the USB-C device manufacturer. We suggest contacting the manufacturer of your device to find out if your computer supports video over USB-C. Thunderbolt 3 will, by default, support at least one display, and in some cases even dual displays. Unfortunately, there is not an adapter that will add DP-Alt mode to a port that doesn’t natively support it.

      Hope this helps!
      Danielle

  14. Jan 2 weeks ago

    Hi, I’d like to connect my iPhone 5 (lightning) to a portable monitor that has usb-c connector (ASUS MB16AC). Is there any way to output a video from iPhone into usb-c? Actually the monitor requires power via the same one usb-c connector so I would need some kind of usb-c splitter to be able to supply power as well. Any tip is appreciated.

    • Danielle 2 weeks ago

      Hi Jan. Your ASUS MB16AC display requires a source that has USB-C out with DP Alt Mode. Alternatively it will work with computers that have USB-A ports, provided they are running one of the displays supported operating systems. Unfortunately, at this time, there is not a way to convert your Lightning connection to USB-C with DisplayPort.

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