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I'm a bit confused about the USB 2.0 portion of a USB-C pinout.

We have two cameras that operate over USB-C, but they are also compatible with USB 2.0 because we can use them successfully through USB 2.0 when plugged into our laptop.

Our actual flight board will be connected to our embedded OS through some traces on the circuit board in the image below, so I'm trying to figure out if I need to put the USB 2.0 traces on pins A6&7 or B6&7, based on the standard USB-C pinout. The cameras seem to be reversible because I flipped them around in the USB-C cable and they still work over USB 2.0 on our laptop.

What I'm not sure about is if it's the camera that is hardwired to be reversible, or is it something in the USB-C cable itself that is making it reversible? If the camera is hardwired to be reversible then it doesn't matter which side I put the traces on, but if it's the cable itself I'm not sure how I can know for sure which side to put the traces on on my surface mount USB-C connector.

I reached out to the company and they haven't been very helpful.

The cameras are: DFM 37UX178-ML and DMM 37UX178-ML Embedded system is: Toradex Colibri iMX6 256MB IT

PCB Layout

ocrdu
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Luc Charbonneau
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1 Answers1

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With USB C 2.0, on the receptacle side, both the A and B sides are wires up. This creates small stubs, which aren't an issue with the low speeds of USB 2.0. You also need to wire up A5 to a 5.1k resistor to ground, and B5 to another 5.1K resistor to ground. This is required for the connection detection part (without this, an dual role device won't communicate)

With an plug, you only wire up the A side, and wire up A5 to an 5.1K resistor to ground

(Note that on the source instead of sink side, the resistors to A5 and B5 (A5 only in the plug) need to be 56K to 5V)

For understanding the differences between the term sink a source, a sink is like a keyboard/mouse, it consumes power from the USB it is attached to. It also obeys command from the device connected to the cable. A source is like a desktop PC. It sends power and USB commands though the cable. When using an C to C cable, It first sends limited current though the CC wire, and it detects a valid connection with the A5 and B5 resistors. Once it detects a valid connection, it will apply 5V. This process makes USB C immune to wrong connections like charger to charger or desktop pc to desktop pc

Ferrybig
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