Cursed USB-C 2.0 Device Exploits Type-C's (Not Completely) Reversible Orientation

Two prominent features of the USB Type-C connector are USB 2.0 backward compatibility and a reversible orientation. Mechanical engineer Pim de Groot has done the seemingly impossible with the Cursed USB-C 2.0 device. It operates differently depending on which way the connector is oriented. But how?!

"I'm not recommending you make your own variant of this, but if you encounter problems with your USB-C devices you might want to try to flip the connector." — Pim de Groot

The secret behind the magic board is quite simple. The USB Type-C pinout on the receptacle side is symmetric. However, the plug is not.

There are several signal groups defined in the USB-C pinout. It contains high-speed differential lanes, communication channels for Power Delivery (PD), side-band signals, Power, and a pair labeled DM/DP. These D+ (DP) and D- (DM) signals enable backward-compatibility with the USB 2.0 specification. The trick up the Cursed USB 2.0 device's proverbial sleeve is that USB-C only contains one set of these signals on the plug side.

de Groot took advantage of having two pairs of these signals on the receptacle side. Each USB 2.0 pair connects to a separate SAM D11 microcontroller. Checking to see if a valid USB connection is available, the MCUs blink their LED red or green.

Interestingly, the USB Type-C specification is not precise when using the standard with two USB 2.0 PHYs in one device. It only covers the case of a single PHY.

Despite the intriguing result, de Groot does not recommend implementing this "feature" in your design. The USB designers intended for the receptacle's pins to be tied together. However, since the spec doesn't cover this use case, it appears to be a legal implementation!

The Cursed USB-C 2.0 device may not have practical day-to-day use. However, it cleverly demonstrates the reversible connector we have all come to love does have a slight difference depending on its orientation.