What is DP Alt Mode for USB-C port? [#041719]
DP Alt Mode is DisplayPort Alternate Mode. DP Alt Mode is a functional extension built into SOME USB-C port. There is two types of USB-C port, with DP Alt Mode and without DP Alt Mode (only as a data port). If your system’s USB-C port comes with DP Alt Mode, it can have DisplayPort functionality for primary or secondary HDMI display. If your system’s USB-C port do not have DP Alt Mode, connecting to a video adapter with HDMI will give you a blank screen.
These DP Alt Mode carry non-USB signals and are optional capabilities unique to the USB-C connector or port, like DisplayPort or Thunderbolt 3. All Apple systems with Thunderbolt 3 can be used with USB-C with DP Alt Mode. Most USB host controller add-on card with USB-C port on Windows systems does not have DP Alt Mode function.
Please check with the system or addon card manufacturer to verify support for USB-C with DP Alt Mode capability before purchasing a USB-C adapter with HDMI port.
Do the UGT-PC371AC USB-C port support support DP Alt Mode? [#05182020]
The UGT-PC371AC is a PCIe USB 3.1 Gen 2 Host card with USB-A and USB-C port.
The USB-C port on this card does not support DP Alt Mode.
It is important for you to understand why it will not support and so that you can have a better understanding of the USB-C technology.
For a USB-C port to provide or support video capability, it MUST support the DP Alt Mode function.
The physical USB-C connector/interface consists of a series of USB pin signals. This signal may or may not include the DP Alt Mode signal.
If you purchase a laptop or desktop system, it may have a USB-C port. That USB-C port can have the DP Alt Mode signal or it may not depend on the design by the system manufacturer.
If the USB-C port DOES HAVE the DP Alt Mode pin signal and function, you can connect an adapter to output HDMI display.
If the USB-C port DO NOT HAVE the DP Alt Mode pin signal and function, it is considered a pure data port, it will not support any adapter to output HDMI display.
DP Alt Mode is video signals, they are not data signals.
DP Alt Mode signal comes from the video controller directly, it cannot go through the PCIe bus because the PCIe bus does not have the DP Alt Mode pin set or can pass the DP Alt Mode signal.
This is why a PCIe USB Host controller card like the UGT-PC371AC will not be able to provide DP Alt Mode function. Simply because it cannot provide any video signal (DP Alt Mode) be itself or gets it from the video card through the PCIe bus.
If you get a video card that has a USB-C port on it, very likely it will have the DP Alt Mode because the video controller can route the DP Alt Mode signal straight to the USB-C port on that same card.
You may also want to know since the UGT-PC371AC USB-C does not support DP Alt Mode, how can I get this to work. The answer is not possible, since the DP Alt Mode signal is not there.
The only way is to find a USB-C Host controller that also has a video controller built on the same card with DP Alt Mode OR get a video card that has USB-C port with DP Alt Mode support.
Look at this FAQ to understand more about the DP Alt Mode.
