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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!

49 Comments

  1. Horst Wischnat 2 years ago

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

    • Susan Mutterback 2 years ago

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

  2. anilroy 2 years ago

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

  3. Paulus 2 years 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 2 years 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 years 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

    • Gagarin235 9 months ago

      I think i have seen pci-e usb-c adapters with dp-alternate mode passthrough …
      something like this .. https://www.amazon.com/SUNIX-USB-C-Express-Alternate-Mode-UPD2018/dp/B01MY4WRBU
      Depending on HOW small your mini gaming rig is, it could be your solution …

  5. Carson 2 years 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 years 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 2 years 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 2 years 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 2 years 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 2 years 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 2 years 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 1 year 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 1 year 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 1 year 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 1 year 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 1 year 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 1 year 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 1 year 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 1 year 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 1 year 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 1 year ago

      Hi Drake,

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

      Thanks!
      Danielle

  13. John 1 year ago

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

    • Danielle Mayea 1 year 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 1 year 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 1 year 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.

  15. David Johnson 11 months ago

    Hey I was wondering if my gaming laptop only has a usb-c port and my monitor supports 144hz only with DisplayPort 1.2 if I got a usb-c to DisplayPort 1.2 adapter the 144hz would work on external monitor
    Try to email me the answer if possible

    • Danielle 11 months ago

      Hi David! We have emailed you regarding your question. Thanks!

  16. Scott 10 months ago

    I am trying to send video out from my display port on my laptop to my docking station. My docking station uses a USB C input. My monitors connect to my docking station. Is there a cable with a male connector that I can connect my laptop and USB C male connector I can connect to my docking station?

    • Danielle 10 months ago

      Hi there! There are some details we’ll need to clarify to help find a solution. A representative from our technical support team will be reaching out to you to provide further assistance.

  17. Bart 10 months ago

    Hello to all!
    My question:
    I need a thunderbolt 3 cable of 2m (6 foot) that support (DP ALT) mode for USB-C at full dataspeed.

    I read somewhere that the only TB3 cables that could support full dataspeed have to be active (not passive). But those active cables doesn’t support (DP ALT) mode for USB-C.

    Is this true? Kind regards, B.

    • Danielle 10 months ago

      Hi Bart! Thanks for your question. Our technical support team has reached out to you directly to help clarify.

  18. Alex 9 months ago

    Hi

    I’m about to purchase a Dell S2719DC Monitor which includes a USB C input which supports DP Alt Mode.

    Is it possible to connect the DisplayPort on my AMD Radeon RX480 graphics card to the USB C input on the monitor with a DisplayPort to USB C cable?

    • Danielle 9 months ago

      Hi Alex! Unfortunately our Type-C to DisplayPort products are not Bi-Directional so they would only work with Type-C on the host and DisplayPort on the displays. As the display can support up to 2560×1440 at 60 Hz, we would recommend the DP2HD4KS and then an HDMI cable to take advantage of the HDMI input on that display. Hope that helps!

  19. Danny 8 months ago

    Hello, I am looking for confirmation of my findings. I have a X99 Taichi motherboard
    https://www.asrock.com/mb/Intel/X99%20Taichi/#Specification

    I have six 4K monitors connected and I am trying to use the NVIDIA surround display option on 3 of the screens. But unfortunately, NVIDIA only allows 1 accessory display monitor/port. Now I read to still be able to use the other 3 monitors with the 3 monitors in the NVIDIA surround configuration, you need to use onboard video. Well my motherboard doesn’t have onboard video :-/ so I was trying to use the USB-C port to display the 2 remaining monitors. But I cant seem to get them to display through the StarTech adapter (MSTCDP122HD). I think my motherboard does not support the DP Alt Mode over USB Type-C. Any help would be greatly appreciated.

    • Danielle 8 months ago

      Hi Danny!

      It is very possible that the X99 Taichi motherboard may not support DP Alt Mode with MST over USB-C. If this is the case, then the MSTCDP122HD will not function properly. We recommend contacting the manufacturer and asking if multiple displays are supported through the USB-C port to confirm. If the manufacture confirms that this should work, then make sure to check the monitor resolutions, as the highest supported resolution through the MSTCDP122HD is 3840×2160 @ 30hz.

      Please feel free to reach out to our technical support team directly for more help and troubleshooting. We’re available via phone at 1-800-265-1844 or live-chat.

      Thanks!

  20. Harley 8 months ago

    Hi,
    I was having a terrible time trying to connect a Surface GO, and a Note8 (Pie) to a M169AC+ – no usb-c to usb-c cable appeared to work (I even bought an Anker Powerline cable to test) until I managed to find the original cable – once I plugged it in it just worked on both devices – successfully triggering DeX on the Note8. Is there something special about DP Alt mode that requires a certain type of cable ?

    • Danielle 8 months ago

      Hi Harley,

      We recommend, first and foremost, ensuring that the USB-C cable supports video. Second, it looks like the monitor you mentioned above may be powered by the USB-C port which means that you’d also require power delivery. The previous cables you tried may not have supported these features. A cable like USB31C5C1M may be a good option for what you’re looking for.
      I hope this helps a bit.
      Please feel free to reach out to our Technical Support team directly if you have any other questions or concerns about your specific configuration. https://chat.startech.com/?lang=EN

  21. Steve 8 months ago

    Hi
    i have an HP envy 13 with usb 3.1 type c that supports displayport 1.2 and i want to connect it to my external monitor, it has vga input, however i bought a usb c to vga adapter and it didnt work, this article says it can be done, did i buy the wrong adapter or what? any help is appreciated

    • Danielle 8 months ago

      Hi Steve – Our team will be reaching out to you directly to help!

  22. Mike Giovaninni 6 months ago

    We have seen an issue with the Intel NUC systems where the display connected to USB-C will disconnect from the system, and only remedy is to disconnect the cable and in some cases, restart the NUC. We have been using StarTech USB-C adapters to convert from both USB-C to HDMI as well as USB-C to DVI. In those cases where we have had Display Port available on the monitors, we have seen fewer issues with USB-C to Display Port adapters. We’ve updated the USB-C firmware on th NUC’s to no avail. Intel thus far has been about as much help as a whip socket on a jeep.. Any suggestions? (Monitors so far has been mostly Planar PLL and PXN series displays, but we’ve also seen it with other brands.

    • Danielle 6 months ago

      Hi Mike. Thank you for bringing this to our attention. Our team has reached out to you directly to try to help troubleshoot.

  23. David 5 months ago

    Hi, I want to build an ITX PC and use a portable display so that it’s relatively easy to carry around. I picked a graphics card with USB-C port on it, this means I can safely assume that it supports DP Alt mode and I can connect my display to my graphics card right?
    This is the graphics card I’m referring to: https://www.gigabyte.com/us/Graphics-Card/GV-N2060AORUS-X-6GC-rev-10#kf

    • Danielle 5 months ago

      Hi David,
      Our team tested this on an Asus RTX 2070 Dual to a Dell U2518D over USB-C to DP-Alt mode. It worked fine in this scenario so we believe it should work with yours. If not, please reach out to our technical support team.
      Thanks!

  24. Hani Ghannam 2 months ago

    Hey,
    I have an Asus ROG mobile and i recently bought this promate unihub c4 that is supposed to allow screen mirroring to a larger monitor. It doesn’t seem to be working, is there anything i am missing on here or is it just that the mobile doesn’t support this type of transfer over cable

    • Danielle 1 month ago

      Hi Hani! Thanks for checking out our blog. We recommend contacting your phone’s manufacturer (ASUS) to help you troubleshoot.

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