--- title: "USB-C alt modes" question: "What can a USB-C port carry besides USB?" url: "https://nearfieldnotes.com/videos/usb-c-alt-modes/" site: "Near Field Notes" video: "https://nearfieldnotes.com/media/usb-c-alt-modes/full.mp4" duration: "1:51" date: "2026-11-05" note: "https://nearfieldnotes.com/notes/usb-c-alt-modes/" --- # USB-C alt modes (video) What can a USB-C port carry besides USB? 1:51, with sound. [Read Note 23](https://nearfieldnotes.com/notes/usb-c-alt-modes/) for the full answer, with figures, conditions and sources. ## Transcript 24 pins. At least 12 different ways to take them over. Plug something in, and the two ends talk over one pin first, the CC pin. If they agree on a mode, a switch chip rewires the rest. Plain USB uses 2 of the 4 fast pairs, plus the old USB 2 pins. DisplayPort takes the other 2 for video. Or all 4. Thunderbolt and USB4 take all 4, and carry video, PCIe and USB at once. Then there's the graveyard. MHL was built for phones. The chips shipped in 2015. I couldn't find one phone that used it. HDMI got its own mode in 2016. In 2023, HDMI's licensing body said no adapters exist. Two resistors to ground turned the USB 2 pins into a headphone jack. Deprecated in 2023. And VirtualLink, for VR headsets. NVIDIA, AMD, Valve, Oculus and Microsoft backed it, and RTX 20 cards shipped with the port. It moved 10 Gb/s USB onto the USB 2 pins. A normal cable has one thin pair there, so VirtualLink needed its own cable. Dead in 2 years. Then the hidden ones. A Chromebook debug cable puts the security chip's own USB on the sideband pins. Apple sends a hidden message that turns them into a serial port. Google has a mode just for updating its adapters. NVIDIA has a test mode. And the Switch 2 and its dock trade more than 30 secret messages before you get a picture. One you might hit today. Set a USB-C monitor to high resolution, and the video takes all 4 fast pairs. Its USB ports drop to USB 2. Here are all 12. --- Source: https://nearfieldnotes.com/videos/usb-c-alt-modes/