USB-C Introduction: What is USB-C DisplayPort (DP Alt Mode)

USB-C is the latest iteration of the USB interface’s connector developed by the USB Implementers Forum. The USB-C was created to be the definitive connector for all consumer electronic users, so that any and all devices could utilize the same connector to transmit data and/or power. Physically speaking, it features 24-pins within an oval-like design. It’s about half the size of the earlier version and commonly used USB-A connector, and roughly equivalent to the size of a Micro-USB connector.

Because of the overarching goal of making USB-C as universal as possible, the engineering behind the USB-C connector was meant to support a wide variety of specifications beyond the standard USB transmission specifications. Some even describe the goal of the USB-C as being “one connector to rule them all”. Perhaps the connector was meant to act as a blank canvas for various data and power transmission interfaces to apply their technology.

The USB-C connector's design gives it four distinct capabilities:

Whereas USB-A connectors have to be plugged into their ports in a specific orientation, the symmetry of the oval shaped USB-C connector head, along with the pin configuration within it, allows the USB-C connector to be completely reversible. It can be plugged in any orientation, thereby adding a greater level of convenience to the already widely enjoyed functionality of the USB interface.

As described above, USB-C from its onset was specifically designed as a vehicle not only for the standard USB transmission specifications, but also for an array of non-USB transmission technologies and specifications. As a result, the USB-C connector features an Alt-Mode capability. This Alt-Mode allows it to support various transmission interfaces, such as the DisplayPort display interface or the Thunderbolt interface. In other words, for some devices, DisplayPort and Thunderbolt data/video signals are able to be transmitted via the device’s USB-C ports depending on the device’s level of support. Read more on this below.

Another feature of USB-C that further bolsters its overall flexibility is its Power Delivery 3.0 technology. It provides up to 100W of charging, but also allows for two-way charging. With two-way charging, a USB-C port has the potential to either output power in order to charge a connected device or input power from a connected device in order to charge itself. What does two-way power charging mean for laptop users, for example? You’ll not only be able to charge your laptop via the same USB-C port that you use to transfer files, but you’ll also be able to let your laptop charge your smartphone using that same USB-C port.

USB-C has the ability to convert digital audio into analog sound. As most users of newer generations of smartphones know, brands are increasingly eliminating the headphone jacks in order to accommodate the device’s hardware. They can replace it with a USB-C port because of USB-C’s ability to convert digital audio into analog sound. It allows users to still be able to use their 3.5mm headphone plug with their smartphone by using a simple adapter.

Despite all the capabilities described above, it is important to note that not all USB-C products support USB-C’s full functions. Of the four features listed, only connector reversibility is a feature inherent in all USB-C connectors/ports. For the remaining three capabilities, their level of support depends on the cost-related hardware decisions made by the manufacturers of the products utilizing them. By design the USB-C has flexibility that allows manufacturers to pick-and-choose the level of USB-C functionality available in their product designs. Brands who might want to target a low-to-mid price point, the USB-C port on their product might only support the data speeds of the newest version of the USB specifications (USB 3.2 Gen2). But, a brand more focused on the high-end market might have products with USB-C ports that support Power Delivery 3.0 and Thunderbolt Alt-Mode.

One of the main draws for USB-C, as well as one of the main sources of confusion, is its Alt Mode capability. As described above, Alt Mode allows USB-C ports to transfer data/video via multiple interfaces, including the increasingly popular DisplayPort video interface. USB-C ports capable of transferring DisplayPort signals are either called USB-C DisplayPort or DP Alt Mode. They allow you to connect video sources (e.g. PCs, Blu-Ray players, etc.) and display devices (e.g. TVs, projectors, etc.) that support DisplayPort to each other via their USB-C ports to broadcast high-definition video.

The confusion over USB-C DisplayPort arises because not all USB-C ports feature DisplayPort Alt Mode functionality (as explained in the previous section) and because of the lack of clarity many brands provide over the level of support their USB-C products have with regards to DisplayPort functionality. As a consequence, a lot of users with devices that feature USB-C ports are entirely unaware of whether or not those ports support DisplayPort over USB-C. The key for these users is to understand how to identify whether their USB-C device supports DisplayPort over USB-C.

Given the confusion over USB-C DisplayPort, the next logical question is “How do I know if my device supports DisplayPort over USB-C?”. There is currently no standard way to identify a USB-C DisplayPort directly on the device, and some brands don’t even bother printing the DisplayPort logo on the ports that support it for their products. The best method to decipher whether your device supports DisplayPort over USB-C is to check either the product specs on the manufacturer’s official website or to check websites with in-depth product reviews and/or information. Within those sites you’ll be able to find detailed breakdowns of each port on the device.

Similar to the confusion around USB-C DisplayPort Alt Mode, there is confusion around whether USB-C and the Thunderbolt transfer interface made popular by Apple products are compatible. The simple answer is that its Alt-Mode functionality also allows USB-C to support the Thunderbolt 3 version of the Thunderbolt interface.

Just like not all USB-C ports feature DisplayPort Alt Mode functionality, not all USB-C ports feature Thunderbolt 3 functionality. Thunderbolt 3 functionality must be explicitly designed into a device’s USB-C port by its manufacturer in order for the USB-C port to be able to support Thunderbolt 3 connections.

For Mac users, the newer generation of Mac devices, including the iMac Pro^®, iMac^® 2017, Mac Mini^® 2018, MacBook Air^® 2018, and all MacBook Pro^® released from 2016 on, do support USB-C Thunderbolt 3 ports. However, it’s worth double-checking official product specs, especially for non-Mac users, to confirm the level of support for the device’s USB-C ports.

One last item of note for users of devices with Thunderbolt 3 ports. Thunderbolt 3 itself also supports DisplayPort functionality. This means Thunderbolt 3 ports also will be able to transmit video to DisplayPort devices.