USB C over ALT Mode

What is DisplayPort™ over Alt Mode?

Some History: In 2014 there was the very first introduction of the USB-C Alt mode, DisplayPort Alt Mode. By remapping the USB-C high speed data pins from USB data to DisplayPort data, it became possible to use a USB-C port as a DisplayPort video output, and in some cases even mix the two to get both USB 3.x signaling and DisplayPort signaling over the same cable. As a result of DisplayPort Alt Mode’s release, the number of devices with video output has exploded, and in laptops especially, this has become the preferred mode for driving video outputs when a laptop doesn’t have a dedicated HDMI port.

USB-C and DisplayPort. 
The DisplayPort protocol, which used to have a unique connector, is now transferred through the USB-C connector. The Type-C connector delivers DisplayPort technology via an Alternative Mode (Alt Mode). 

With USB-C you get:
  • USB 3.1 Gen 2 data transfer rates of 40Gbps
  • USB Power Delivery 2.0 – Up to 100W of bi-directional power delivery
  • DisplayPort Alternate Mode (DP Alt Mode) with DP 1.4 support
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 supported display protocols.

    What is DisplayPort™ over Alt Mode?

    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

    What to Check: DisplayPort™ over Alt Mode.
    First things First!
    • Always check the specification of the devices you are going to use. So the Laptop, PC or another source device.
    • Also check the specification of the connecting cables and adapters you are using (also if there Uni- or Bidirectional).
    • Check the specification of the required output device.
    • Make sure they support the USB C over Alt Mode!

    How To Check: The Usb C Port Version/Type.

    What does the USB C port look like?
    The USB C port is an oval port. The port is also smaller than a USB A. In addition, the USB C connection is symmetrical. For example, you can insert a USB C plug into a USB C port in 2 ways.

    How To Check: The Usb C Port Version/Type.

    What type of USB C port does my Windows laptop have?

    Next to the ports of a Windows laptop are symbols / logos, which indicate what you can do with the port.

    • Is there a symbol of a lightning (Thunderbolt 3) next to the USB C port? Then you can charge via this port and pass on a video signal and thus connect a monitor. This port supports DisplayPort alt mode.
    • Is there a symbol of a D (DisplayPort) next to the USB-C port? Then you can pass on a video signal via this port and thus connect a monitor. This port supports DisplayPort alt mode.
    • Is there a symbol of a battery next to the USB C port? Then you can charge your laptop via this port. This port does not support DisplayPort alt mode.

    What type of USB C port does my Windows laptop have?

    USB C port Apple Mac

    What type of USB C port does my MacBook have? With MacBook, there is no logo or symbol next to the gate. 

    What type of USB C on my Apple Mac
    Function USB C Model MacBookVideo signal / Support  DisplayPort alt modeCharging
    MacBook Pro 2016-2019YesYes
    MacBook Pro 2015NoNo
    MacBook Air 2018-2019YesYes
    MacBook Air 2015-201NoNo
    MacBook 12 inch 2015-2017YesYes
    Check latest spec at apple.com*
    *All brands and trademarks belong to their respective owners.

    On a MacBook, follow these steps:
    • Start up the MacBook.
    • On the desktop at the top left, go to the Apple logo and click on it. Click on “About this mac”.
    • Check which model / introduction year you have.
    • Use the diagram below to see what you can do with your type of USB C on the MacBook. This port supports DisplayPort alt mode.
    • Also see the website of www.apple.com for all models.

    USB C port Apple Mac

    What about: Drivers and firmware updates

    What about: Drivers and firmware updates To get the most out of the connection. You may need to do some driver and/or firmware updating. So the best screen resolution and data speed will be available.

    • It is advisable to update the driver or firmware of your device to fix device issues and to take advantage of enhancements that are not available in previous versions.
    • NOTE: Update and Firmware processes may vary depending on your device’s manufacturer and its operating system (OS) off the device. See their READ-ME files and installation instructions before execution. 
    • IMPORTANT: Read the user manual of your devices to find out where and how to find the current system/firmware version of your devices.

    DisplayPort™ Over USB C Technical Details

    DisplayPort™ leverages the Alternate Mode Functional Extension of the USB Type-C interface, and shares similar electrical characteristics with USB 3.1, allowing use of common system elements. 

    • Video, SuperSpeed USB and power, all on one connector
    • 4K @60Hz 24-bit color (without compression) with simultaneous USB 3.1
    • 5K (5120 x 2880) display support without compression with simultaneous USB 2.0
    • Support for BT.2020 color space, HDR, and HDCP 2.2
    • 8K x 4K display support with use of 4:2:0 pixel structure (good) or VESA Display Stream Compression (better)
    • High-end multichannel audio support
    • Backward compatible with VGA, DVI, and HDMI 2.0 with CEC using plug adapters or adapter cables
    • Extensible packet-based data structure


    Please refer to a full overview of our Legacy Terms and Conditions on www.club-3d.com.

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