USB-C breakout/Using it/09. USB 2.0 data, and what is missing
Using it · 09 of 11

USB 2.0 data, and what is missing

Two data pads, four contacts in the socket, and no SuperSpeed at all. The bridge that makes the plug work either way up is the same decision that caps this board at USB 2.0.

Four contacts, two pads

Inside the socket, the USB 2.0 pair appears twice — once in each half of the connector, so there is a set the right way up whichever way the plug goes in. The board joins them: the two D+ contacts become one D+ pad, and the two D− contacts become one D− pad.

Two pads, four contacts, one pair
bit 1 of 8
Data pads
2
Socket contacts
4, joined in pairs
Speed ceiling
USB 2.0
The board joins the socket’s two halves, so the plug works either way up. A6 and B6 become one D+ pad, A7 and B7 become one D− pad, and whichever half the plug happens to use is the half that carries your byte. That trick is what costs you USB 3: the SuperSpeed pairs and the SBU pins have to stay separate to be useful, so they are simply not brought out. This is a USB 2.0 board — good for serial, keyboards, and anything that would have been happy on a micro-USB socket.

That bridging is why you get one pair of pads instead of two, and why the pair works regardless of orientation. It is also the reason this is a USB 2.0 board and not a USB 3 one — the SuperSpeed pairs only mean anything if the two halves stay separate, and bridging them would destroy the signal. So they are simply not brought out. Nor are the SBU pins.

What you get

VBUS, GND, CC1, CC2, D− and D+. That is enough for:

  • power, which is what most people want;
  • USB 2.0 at low, full or high speed — keyboards, serial adapters, anything that would have been happy on a micro-USB socket;
  • measuring what the source is advertising, which is the next chapter.

What you do not get

No SuperSpeed pairs, so no USB 3 rates. No SBU, so no alternate modes and no DisplayPort. No Power Delivery, because that needs a chip rather than a resistor.

If the thing you are building needs any of those, this is not the board — but be honest about whether it does. A great deal of hobby USB work is a serial adapter or a device that enumerates at 12 Mbit/s, and every bit of that fits inside USB 2.0.

Wiring the pair

Keep D+ and D− together and short. They are a differential pair: the signal is the difference between them, and that only survives if the two wires see the same interference, which means running beside each other.

On a breadboard, put them in adjacent rows and do not route anything noisy between them. Share the ground — the pair needs a common reference, and a data connection with no shared ground does not work no matter how correct the two signal wires are.

Both D pads are between CC1 and CC2 in the row, with D− first. Crossing the pair is the commonest wiring mistake here, and it produces a device that never enumerates rather than an obvious fault.

When it does not work

I wired D+ and D− and nothing enumerates

Check the pair is not crossed first — D+ to D+, D− to D−, and the two wires kept side by side and short. Then check that the ground is shared: a data pair with no common ground has no reference and will not work even though both wires are correct. If it still fails, remember this board has no host circuitry in it; something at the other end has to be a USB host.

My USB 3 device only runs at USB 2 speed through it

That is the ceiling of the board, not a fault. The SuperSpeed pairs and the SBU pins are not brought out to the header at all — only VBUS, GND, the two CC lines and the USB 2.0 pair. Any USB 3 device will fall back to its USB 2.0 mode, which is what it is designed to do when the fast pairs are absent.

Can I use long wires for D+ and D−?

Not really. A USB 2.0 pair at full speed is a 480 Mbit/s differential signal that expects a controlled-impedance pair, and jumper wires on a breadboard are neither controlled nor a pair. Short and side by side will often work for low and full speed; expect trouble as soon as the wires are long, separated, or routed near anything switching.

Which pad is D+ and which is D−?

Counting from the square pad at the top: GND, VBUS, CC1, then D−, then D+, then CC2. D− comes first. Both faces of the board are labelled, so check the silkscreen rather than counting if there is any doubt — getting the pair crossed is the commonest wiring mistake on this board.

Where this goes next

An ESP32, one wire to a CC pad, and a sketch that prints which way up the plug went in and how much current you have.

Read what the charger offers

Edit this page — content/books/usb-c-breakout/usb-2-0-data.mdx

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