Displayport alt mode

DisplayPort Alt Mode (DisplayPort Alternate Mode) is a feature of USB-C that allows a DisplayPort signal to be sent over a USB-C cable. It is defined by the Video Electronics Standards Association (VESA) in the "DisplayPort Alternate Mode on USB Type-C" standard, which VESA published on 22 September 2014 in liaison with the USB 3.0 Promoter Group. The mode repurposes some or all of the four high-speed lanes in a USB-C cable to carry DisplayPort signals, while USB 2.0 data and USB Power Delivery remain available over their own wires.

It is used by some AR glasses. Tethered display glasses such as the Xreal Air plug into a host device whose USB-C port outputs DisplayPort, so whether a given phone, laptop or handheld console supports DisplayPort Alt Mode decides whether the glasses work with it directly. A related USB-C alternate mode for PC VR headsets, VirtualLink, was announced in 2018 and abandoned in 2020.

Reviewed 27 September 2026. Checked every cited VESA, Texas Instruments, Unigraf, Xreal, Apple, Valve and press source against the specs, dates, version history, host-support and VirtualLink claims it supports. About review dates.

How it works

A full-featured USB-C to USB-C cable has four high-speed differential pairs (two transmit and two receive pairs for SuperSpeed USB), a USB 2.0 pair, two sideband-use (SBU) wires, a configuration channel (CC) wire and power and ground wires. In DisplayPort Alt Mode the high-speed pairs are switched from USB to DisplayPort main-link lanes. VESA's 2014 feature summary lists the other signal assignments:

• the DisplayPort AUX channel uses the SBU pins;
• the DisplayPort hot plug detect (HPD) and interrupt signals are sent over the CC pin using the USB Power Delivery protocol;
• USB 2.0 and USB Power Delivery are available in every configuration, because they use dedicated wires in the cable.

Alternate modes are negotiated over USB Power Delivery with vendor defined messages (VDMs); the communication is specific to each mode's standard or vendor ID (SVID). VESA's compliance tests for DisplayPort Alt Mode check the Discover SVIDs and Enter Mode sequences and the Status Update commands exchanged between the display source and the sink, along with VBUS, VCONN and HPD timing. Because the USB-C plug is reversible, the device with the receptacle detects the plug orientation through the CC pin and routes the signals to the correct pins with a switch or multiplexer.

Either end of a USB-C link can independently be the USB host, the power consumer and the DisplayPort video source; VESA describes these roles as orthogonal to each other. VESA presented the two-lane DisplayPort plus USB configuration as useful for docking stations and hubs, or for adding docking station functionality to a display.

Pin assignments

The standard defines several ways of mapping DisplayPort signals onto the USB-C pins. According to a Texas Instruments application report, six pin assignments (A to F) are defined for a USB-C port acting as a display source and five (A to E) for a port acting as a display sink. Assignments A to D are intended for USB-C to USB-C cables and for adapters to other video standards such as VGA, DVI and HDMI; E and F are intended for adapters from USB-C to DisplayPort plugs or receptacles. The three assignments described by the test-equipment maker Unigraf are:

Assignment	High-speed lanes used for DisplayPort	Other use of the high-speed lanes	Typical use
C	Four	None	USB-C to USB-C cables and video adapters
D	Two	Two lanes carry SuperSpeed USB data	Docks, hubs and displays with USB ports
E	Four	None	USB-C to DisplayPort adapters; at the sink's USB-C receptacle, main link and AUX polarity are inverted relative to C

Adapters

A USB-C to DisplayPort adapter cable carries four DisplayPort lanes and works with legacy DisplayPort sources and sinks, but it does not support USB (other than USB Billboard) or other alternate modes. Adapters and adapter cables to HDMI, DVI and VGA contain a DisplayPort protocol converter. USB-C does not support DisplayPort Dual Mode (DP++), and VESA's 2019 presentation states that USB-C to HDMI converters support up to HDMI 2.0b and CEC.

Bandwidth and resolution

VESA's 2014 announcement said that USB-C lanes can carry SuperSpeed USB data at up to 10 Gbps per lane or DisplayPort at up to 8.1 Gbps per lane, the HBR3 rate defined in DisplayPort 1.3. At 5.4 Gbps across all four lanes the mode supports 4096 x 2160 at 60 Hz with up to 30-bit color, and two lanes at 8.1 Gbps can drive a 3840 x 2160 monitor while the other two lanes carry SuperSpeed USB data. VESA noted in 2019 that the two-lane configuration is common for USB-C DisplayPort Alt Mode. Its figures for DisplayPort 1.4a at the HBR3 link rate are:

DisplayPort lanes	Without compression	With Display Stream Compression (DSC)
4 lanes	5K (5120 x 2800) at 60 fps, 24 bpp	8K (7680 x 4320) at 60 fps, 30 bpp
2 lanes	4K (3840 x 2160) at 60 fps, 24 bpp	5K (5120 x 2800) at 60 fps, 24 bpp

Source: VESA, USB Developer Days 2019. All modes assume 4:4:4 color encoding.

With two lanes, a source limited to DisplayPort 1.2 (HBR2) can drive two 1080p displays or one 4K display at 30 Hz, and an HBR3 source can drive 4K at 60 Hz. For passive cables, VESA's 2014 summary states that cables up to 1 m are designed for SuperSpeed Gen 2 (10 Gbps) and cables up to 2 m for Gen 1 (5 Gbps). Apple, for example, tells iPhone users to connect high-resolution displays with a USB-C cable that supports USB 3.1 or higher, because the cable that comes with the phone supports charging and USB 2 speeds.

DisplayPort Alt Mode 2.0 raised the ceiling to up to 80 Gbps of DisplayPort video over all four lanes, or up to 40 Gbps with simultaneous SuperSpeed USB data. DisplayPort 2.0 delivers a maximum payload of 77.37 Gbps across four lanes (up to 19.34 Gbps per lane), which VESA said supports 7680 x 4320 at 60 Hz with 30 bpp 4:4:4 HDR uncompressed and 15360 x 8640 at 60 Hz with compression.

History

When the standard was announced, Craig Wiley of Parade Technologies, a VESA board member, noted that DisplayPort was already used inside other wired interfaces such as Thunderbolt, DockPort, MyDP and Embedded DisplayPort. VESA announced an early certification program for DisplayPort Alt Mode devices on 8 June 2016; nearly a dozen devices from companies including Intel, Dell, Asus, HP and LG Electronics were certified in its pilot phase. By 2019 VESA reported that more than 200 DisplayPort Alt Mode products (sources, sinks, adapters and docks) had been certified in two years.

Date	Milestone
22 September 2014	VESA publishes the DisplayPort Alt Mode on USB Type-C standard, version 1
8 June 2016	Early certification program for DisplayPort Alt Mode devices
13 December 2016	VESA announces completion of the full compliance test specification (CTS)
24 January 2017	DP Alt Mode on USB Type-C CTS version 1.0 released
3 November 2017	Version 1.0b of the standard, with clarifications to pin assignment E and adapter cable reversibility
29 April 2020	Version 2.0, bringing DisplayPort 2.0 performance and USB4 interoperability
17 October 2022	DisplayPort 2.1 tightens alignment with the USB Type-C and USB4 PHY specifications

USB4 and DisplayPort tunneling

USB4 adds a second way to carry DisplayPort over USB-C: DisplayPort is tunneled through the USB4 link, which VESA describes as an architecture designed to combine multiple protocols (USB, DisplayPort and PCIe) onto a single physical interface. VESA's 2019 summary of the USB4 requirements states that USB4 hosts and hubs must support DisplayPort tunneling, and that USB4 hosts and hubs must also support DisplayPort Alt Mode on all of their downstream-facing ports. The same presentation called continued backward compatibility with the millions of certified DisplayPort Alt Mode products already shipping "critical". Craig Wiley said in 2020 that VESA was "taking care of everything related to high-performance displays over USB-C", whether through a native DisplayPort or USB-C connector or through tunneling over USB4. DisplayPort 2.1 added a bandwidth management feature so that tunneled DisplayPort can coexist more efficiently with other I/O traffic on a USB4 link.

Use in AR and VR

Display glasses

Wired display glasses show a phone, console or computer screen as a large virtual display. Several product lines take their video input through DisplayPort Alt Mode. In its 2023 review of the Xreal Air, GSMArena wrote that the glasses need "a USB Type-C port with USB alt-mode support for Display Port output", that there was no easy way to tell which Android phones had it, and that laptops need DP alt mode listed in their specifications to work directly. Xreal's setup guide for the Asus co-branded ROG XREAL R1 states that "the USB Type-C port must support DP Alt Mode" and that laptops must support USB-C DP Alt Mode or Thunderbolt 4 to connect directly. Xreal's guide for the Xreal One series lists iPhone 15, 16 and 17 models, Android phones and tablets, the Steam Deck and ROG handhelds, Windows laptops with USB-C, the MacBook Pro and the Mac mini as devices that connect without an adapter, and notes that the glasses have no built-in battery and are powered by the connected device.

Devices without DisplayPort output need an adapter or hub. Xreal lists the Nintendo Switch, Switch OLED and Switch 2 as requiring its XREAL Hub, and PlayStation and Xbox consoles and desktop computers with HDMI ports as requiring an HDMI to USB-C adapter. The Xreal Beam accessory accepts DisplayPort over USB-C, can also cast wirelessly, and can connect to a Nintendo Switch, which the glasses alone cannot.

Host device support

Support in phones varies by model. The following examples come from manufacturer documentation and press reports:

Device	DisplayPort over USB-C	Notes
iPhone 15 and later	Yes, on listed models	Apple states that iPhone "uses the DisplayPort protocol to support connections to USB-C displays at up to 4K resolution and 60Hz". Its support page lists iPhone 15 models, iPhone 16 models except the iPhone 16e, iPhone 17 models except the iPhone 17e, and iPhone 18 Pro models. TechCrunch reported in 2023 that the Xreal Air worked "great out of the box" with the iPhone 15 line.
iPhone Air	No	Tom's Guide reported that its USB 2 port does not support DisplayPort, so Xreal and Viture glasses cannot be used with it directly.
Google Pixel 8 series	Yes, since Android 14 QPR3 Beta 2 (March 2024)	Google enabled DisplayPort Alt Mode by default in the Pixel 8 software after initially blocking it; according to Android Authority, Pixel phones before the Pixel 8 had it disabled at the hardware level.
Steam Deck	Yes	Valve lists "Display port over Type C; up to 8K @60Hz or 4K @120Hz, USB3 gen 2".

VirtualLink

VirtualLink was a separate USB-C alternate mode designed for PC-tethered VR headsets. It was introduced on 17 July 2018 by a consortium led by NVIDIA, Oculus, Valve, AMD and Microsoft, and specified four HBR3 DisplayPort lanes, a USB 3.1 data channel for cameras and sensors, and up to 27 watts of power over one cable. Road to VR reported in September 2020 that the standard had been abandoned: the consortium's website had begun redirecting to Wikipedia around July 2020, Nvidia's RTX 20 Super cards dropped the USB-C port and the RTX 30 series did not appear to include it, AMD had not added VirtualLink support to any of its GPUs, and Valve had cancelled its VirtualLink adapter for the Valve Index because the technology "has not been widely adopted by manufacturers, laptops in particular". The VRgineers XTAL was one of the few headsets to implement it.

The ports found a later use. In 2024 UploadVR reported that the PlayStation VR2, whose PC adapter combines a DisplayPort input, a USB-A connection and a DC power input into the headset's single USB-C cable, can be connected directly to graphics cards with a VirtualLink port (some Nvidia RTX 20 series and AMD RX 6000 series cards) without the adapter.

See also

• DisplayPort
• USB-C
• HDMI
• AR glasses
• Tethered AR