How to get USB-C Displayport-Alt mode working with an Asus MB16AHG portable monitor (for Freesync support)?

[xenphor]

I have an RTX 4070 gpu and am trying to get a bi-directional displayport to usb-c cable working with an Asus MB16AHG portable monitor. Right now, when switching to the usb-c input, it says to check with the manufacturer that the source supports displayport output.

I know the cable works (CableCreation 8K Bi-Directional) because I have other monitors I got from Aliexpress that work with it via usb-c. I also know the usb-c input works on the monitor because I have a Surface GO 3 that works with it using a standard usb-c cable. What I can't get to work is displayport from my RTX 4070 GPU to the portable monitor over usb-c. I tried an Amazon Basics Bi-Directional cable and it also didn't work so I'm out of ideas. The reason usb-c is important is that I'm hoping to get Freesync working which does not work over the HDMI input.

I have installed the driver and software that is available on the MB16AHG support page and that didn't help.

Has anyone gotten a setup like this to work? Do I need an actual pci-e add in card to rout the displayport from my gpu and output a usb-c signal from that?

Thanks for any help.

edit: Here's what the AI said:

Your RTX 4070 only outputs video over DisplayPort and HDMI.

It does not support USB-C with DP Alt Mode, nor can it “fake it” through a cable.

Even if the cable’s technically bi-directional, the GPU doesn't know how to send video over USB-C — it lacks the controller for that.

So even with a bi-directional cable, your RTX 4070 can’t talk to a USB-C display like the MB16AHG via that path.

[SprunkiRetake]

I am interested in the solution to this problem!

[Erxandros]

I have also tried a bidirectional cable (Club 3D CAC-1557) with no results using my RTX 3080 or RX 6800. I know the cable works as I have used it on other portable monitors with success. It seems that the firmware on this Asus MB16AHG portable monitor is a bit more restrictive. A purpose built cable might be needed to get it to work. I know that bidirectional cables only send a display port signal and no power or USB data lines. Maybe the firmware of the monitor is expecting power and USB data as that is what DP alt mode also provides. Maybe something like this might work (you can find these cables on Amazon):

71ze+JBpQxL._SL1500_.jpg (81.47 KiB) Viewed 1409 times

I have bought one of these and are going to try it in a week or two to see if it works.

[Erxandros]

After it took a while for the cable to get delivered, I can confirm it works. You need to connect the displayport and power first before connecting the type c to the monitor. USB data connection is not required (if you plug data in, a "Generic USB Hub" will appear in device manager, it might be used for Asus DisplayWidget Center, I am not sure). The cable I bought was this one: https://www.amazon.com/dp/B0BW8QKFHK

I can also confirm the Freesync is working over displayport, range 60 Hz to 144 hz. This confirms my theory that the monitor is expecting displayport with power to even attempt connection with the host. This should not be designed like this, but I am pretty sure the firmware of the monitor can not be updated or changed to fix this.