Add USB-C with DP ALT-mode to your Desktop PC

[Updated 2022/12/15 with L1techs USB-C centralizer]

  1. Introduction
  2. External DP+USB -> USB-C multiplexers
  3. GPU add-in-boards
  4. USB-C+DP-ALT-mode PCIe add-in-boards
  5. Thunderbolt PCIe add-in-boards
    1. Maple-Ridge based TB4/USB4 boards
    2. Titan-Ridge TB3 boards
  6. Integrated mainboard graphics
  7. References & Additional reading 

Introduction

Recently I’ve received several requests from customers who want to share a Docking station with monitor/mouse/keyboard between a Desktop PC and a modern Laptop without using a software solution like Mouse without borders

Many modern laptops feature USB-C or Thunderbolt-3 which makes Docking connectivity simple with a single connector providing power, data, and monitors. But most Desktop PCs lack these ports. A variety of inexpensive PCI express -> USB-C add-in-boards are available, but most are not compatible with monitors connected via Docks because they lack DisplayPort Alt mode support. So I’ve catalogued some solutions to upgrade your Desktop PC to have either USB-C with DisplayPort alternate-mode OR Thunderbolt.

External DP+USB -> USB-C multiplexers

GPU add-in-boards

USB-C+DP-ALT-mode PCIe add-in-boards

Notes:

  • The board only supports a single DisplayPort signal – so only works with 1 monitor, or perhaps two 1080p monitors via a separate MST hub or MST daisy-chaining.
  • To connect your GPU output to the board’s input, you may need a 1 foot DisplayPort -> DisplayPort cable if one doesn’t come in the box
  • Depending on the mainboard PCI slot topology, you may need to place the add-in card in a different slot. Sometimes you’ll need to use the first slot on the board that is typically used for a GPU and connected directly to the CPU. You may also need to change UEFI/BIOS settings to enable PCI lane bifurcation mode (x8/x8) or (x8/x4/x4). In other cases, you may need to use the last slot on the mainboard to ensure that the AIB is communicating through the mainboard chipset rather than through the CPU directly.
  • If you don’t have a spare PCIe slot or the PCI slots don’t work, but you have a spare M.2 NVME slot (not SATA) you can try using a M.2 nVME -> PCIe x4 adapter cable. Other mainboard connectors that can transmit the PCIe protocol can be adapted to PCIe slots as well (OcuLink SAS connector example).

Thunderbolt PCIe add-in-boards

Maple-Ridge based TB4/USB4 boards

  • ASRock Thunderbolt4 AIC (~$100 USD)
    • 5-pin header like GC-TitanRidge-v1.0 – perhaps the best chance of cross-compatibility with off-brand mainboards?
    • dual DisplayPort input
    • dual TB4 out
    • 27W PD capable
  • Asus ThunderboltEX 4 (~$120 USD)
    • 14-pin header suitable for compatible Asus motherboards
    • dual miniDisplayPort input
    • dual TB4 output
    • 100W PD capable when 1x PCIe-6 power cables connected
  • Gigabyte GC-Maple-Ridge (~$100 USD)
    • 5-pin + 3-pin headers
    • dual miniDisplayPort input
    • dual TB4 output
    • single DisplayPort output
    • 97W PD capable when 2x PCIe-6 power cables connected
  • Dell Optiplex TB4 customer upgrade kit (~$150)
    • Similar to ASRock model but with inferior power capabilities and Dell-specific mainboard header
    • dual DisplayPort input
    • dual TB4 out
    • 15W PD output?

Titan-Ridge TB3 boards

Notes:

  • There are several older Alpine-Ridge based boards by Asus, Gigabyte, ASRock, MSI, etc. but with limited compatibility across USB-C accessories and mainboard brands.
  • Depending on the mainboard PCI slot topology, you may need to place the add-in card in a different slot. Sometimes you’ll need to use the first slot on the board that is typically used for a GPU and connected directly to the CPU. You may also need to change UEFI/BIOS settings to enable PCI lane bifurcation mode (x8/x8 or x8/x4/x4). In other cases, you may need to use the last slot on the mainboard to ensure that the AIB is communicating through the mainboard chipset.
  • If you don’t have a spare PCIe slot or the PCI slots don’t work, but you have a spare M.2 NVME slot (not SATA) you can try using a M.2 nVME -> PCIe x4 adapter cable. Other mainboard connectors that can transmit the PCIe protocol can be adapted to PCIe slots as well (OcuLink SAS connector example).
  • Additional compatibility may need custom firmware flashing of the board

Integrated mainboard graphics

Many mainboards using integrated graphics from Intel or AMD don’t have DisplayPort and only include HDMI. In order to use these video outputs with any of the aforementioned solutions, you need to convert the HDMI signal to DisplayPort using a reverse HDMI -> DP adapter.

References & Additional reading 

Special thanks to /u/chx_ for info about the Sunix board and inspiring the article.

19 thoughts on “Add USB-C with DP ALT-mode to your Desktop PC

  1. There now are a few hdmi to USB-C DP-alt mode adapters based on the Lontium LT6711A. For example from UGreen and Delock.

    https://m.nl.aliexpress.com/item/1005001459544376.html
    https://www.delock.com/produkte/N_63251/merkmale.html

    The UGreen can also combine USB 2.0 with up to 4K@60Hz over 4 lanes DP1.2 speeds.
    I have that adapter en seems to work fine with my Raspberry pi 4.

    The chip also supports combining 2 lanes for USB 3 and 2 lanes for DP-alt mode, so that might also become available on other products.

    Like

    • The Delock looks great, but.. only 5V usb? it usually means 1.5A, so 7.5W, nowhere near the 60W common for usb-c power delivery.. I’m perplexed! Am I missing something?

      Like

      • Yes it is surprising that all these are not offering 5V@3A since pulling 15W from the PCI express slot is no big deal (bucking 12V down to 5V is simple enough).

        Pulling 60W from the 12V line and boost converting it to 15V is a bigger deal and rather expensive so that’s why you don’t see it on these boards. Plus implementing multi-voltage PD is a lot more complex than single voltage.

        Like

  2. Hey @danchar thanks for replying! I was talking about the adapters that Bernard linked, though.. those are not cards! And yet, they boast USB PD specs.. I googled a bit and the USB PD specs seems to mandate a wattage that neither the pci-e cards, much less the adapters, could ever sustain. So how the hell are these suppposed to work with anything requiring more than 5V??

    Like

    • Ok I understand the confusion. PD is 100% optional as part of the USB-C spec. And even if a vendor does claim PD support, all they really need to do is 5V @ 1A. In the case of these adapters, the HDMI and DIsplayPort only provide 5V or 3.3v @ 300mA or thereabouts So the power is coming from an separate micro-usb port which is limited to 5V @ 1A or thereabouts. So these adapters are really not well suited to VR goggles or USB-C portable monitors that consume more than 5W

      Like

  3. Ooooh I see! So they’re for the unfortunate soul who let’s say bought a desktop monitor that only has usb-c as its video input.. I was so hoping for the miracle adapter! I mean in theory the Lontium LT6711A does support PD so it would be a matter of having a usb-in that accepted some real power xD I guess we’ll have to wait

    Like

    • The usecase for the lontium chip is to connect a monitor through either DisplayPort or usb-c to a HDMI output device at 4K@60Hz. A good example device would be a Raspberry Pi 4, that only has a HDMI output (Usb-c to DisplayPort adapters are very simple and cheap and work when chained with the UGreen adapter with the Lontium chip).
      There also is a USB-C to Dual-Link DVI adapter sold with Club3d, StarTech and other branding that works when chained to the UGreen. Allowing users to connect a Dual-Link DVI monitor to the Raspberry Pi 4 through HDMI at the native 2560×1600@60Hz.

      Like

  4. Hi Dan, thanks for the article. I have a scenario for this. Currently I have 2 Thunderbolt 3 laptops and a NUC, and my keyboard and mouse are plugged into a 4K USB-C monitor. This is really nice because I can switch what computer I’m using just by unplugging the USB-C cable and plugging it into the Thunderbolt 3 port on the computer I want. But the NUC is not a super powerful computer. Whatever I get or build to replace the NUC, I want to keep this convenience. I think I understand this article but I want to be sure: using the Sunix upd2018, I can build a PC or buy one and add that card, then it will “play nice” with that monitor and the stuff plugged into it? Does it matter if the DisplayPort signal going into the card comes from integrated or discrete graphics? Does this consume a lot of power (could be a problem if I buy a prebuilt that doesn’t have a lot of juice from some non-upgradeable power supply)? If it all looks good for my case, that’s awesome! It seems a lot easier, cheaper, and more flexible than finding a Thunderbolt 3 card and a compatible motherboard. And it seems like I can also add the card to a pre-built as long as it has the space for the card.

    Like

    • Hi – you have it exactly right. Integrated vs discrete GPU doesn’t matter as long as it is DisplayPort. If integrated only has HDMI, you may be able to use a bi-directional HDMI->DP cable (see my separate article on this), but there are potential compatibility issues with this approach and you may need to plug/un-plug a few times after reboots to get it to sync.

      The Sunix card itself consumes negligible power – unless the downstream USB-C device (like a portable monitor) consumes power over the wire. In that case, the card will draw up-to 15-20 watts. No need for a beefy power supply here. Some of the TB3 / TB4 cards will draw up to 35W when 2 TB3 power-consuming devices are plugged in – still not a big deal. If you’re plugging into a powered USB-C hub, or hub built-into a monitor, you’ll have no issues regarding power.

      Like

  5. This is very useful im going to try the newer wacom display link adapter since the old one is discontinued.

    I need something that has its own power because i am trying to use the nreal light ar headset on my pc.

    I just wanted to say thanks for this post. It was extremely dificult finding devices that supported video from hdmi or displayport out over usb-c.

    Then add the fact that the nreal uses only usbc for audio video and camera with a usbc male plug for input… It’s like the devs were afraid of someone using it on anything other than a phone.

    Liked by 1 person

      • Thanks for confirming this one. I was losing hope in trying to connect my monitor for my desktop and then i stumbled into this one. I have Lenovo L15 monitor which is mostly similar

        Like

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