USB Cheat Sheet (2022)

Excellent article.

If I could offer one correction, it would be that SBU (as specified by the USB 3.0 Promoter Group[1]) means "Sideband Use" rather than "Secondary Bus".

On some devices, it is used to carry UART; on others, audio.

[1]: https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%... (pdf)

Tangent: Author has this fabulous post I'd highly recommend: https://fabiensanglard.net/mjolnir/index.html

I read it once years ago and I come back to it every now and then wishing my current PC (10+ years and going) would gently die so I could finally build something small and tiny.

I actually like the 3.2 naming. Gen is speed, "by" is width. It puts it very roughly on par with PCIe's naming which nobody complains about. I just don't like that USB 3, USB 3.1, and USB 3.2 are the same things. And that sales people don't seem to understand that saying a chip supports 3.1 or 3.2 tells me it's anywhere from 5-20gbps which isn't ideal.

I don't know what short-distance data communications will be like in 2050, but we know it will be called USB.

Good sheet. Worth adding:

- Female vs male crossover naming and pinouts for Type-C connectors

- Actual voltage, modulation and signaling schemes (USB4v2 uses PAM3 11b/7t encoding)

- PD generations and profiles

I once heard that the USB naming is misleading by design so that vendors could still sell older generations accessories they had in stock. The USB-IF just rebrands the old ones to make them sound current.

Imagine the following naming:

  USB 3.0 / USB 3.1 Gen 1 / USB 3.2 Gen 1 -> USB 3 5Gbps
  USB 3.1 / USB 3.1 Gen 2 / USB 3.2 Gen 2 -> USB 3 10Gbps
  USB 3.2 Gen 2x2 -> USB 3 20Gbps

Isn't that much clearer? I think USB 4 is finally going to the right direction.

The wires count is suspect. USB 1.0-2.0 only use two wires for data (the other two are ground and power). USB 3.0 uses 4 for data (plus extra shield, 2 for USB 2.0 and 2 for power). I don't know well enough the others.

I still don't understand why MacBooks support USB4/Thunderbolt 4/5, but NOT USB 3.2 Gen 2x2. So you can get 20-40Gb/s speeds with more expensive external disks, but only 10Gb/s with the cheaper, more commonly available ones that advertise 20Gb/s.

The simplicity of Thunderbolt. Versions 1 and 2 used mini DisplayPort, 3 and upwards USB-C. Version 1 was 10Gbps, 2 was 20Gbps, 3 was 40Gbps, 4 was 40Gbps, 5 is 80 or 120Gbps with boosting.

A Thunderbolt 5 cable will always support 80Gbps, DisplayPort 2.1, PCIe, USB4 and power of up to 240 watt.

This article is why I replaced all the usb dock cables in the office to make sure the usb cable connected to the laptops was transferring enough power so the laptop wouldn't silently lower its frequency for the lower power draw. 10-30% speed bump just because.

Related. Others?

USB Cheat Sheet - https://news.ycombinator.com/item?id=31271038 - May 2022 (168 comments)

> SBU1 and SBU2 are secondary bus wires, for the DisplayPort AUX channel and hot plug detection (HPD).

Correction - HPD signal is translated into vendor message and carried over CC lines - same ones that are used for PD and AltMode negotiation.

In DP-Alt mode SBU1/2 basically becomes AUX+/-.

I’ve been a tech guy for 45 years and I still can’t figure out USB and Thunderbolt and what goes with what and how fast it’s supposed to run.

IMHO USB 3.0 was the last sanely-named version. Then again, if you're familiar with Ethernet, the proliferation of variants isn't unexpected.

I just wish product listings were clear and actually followed the specs.

I'd love for someone who's part of the USB-IF to try and explain what the heck they were thinking with their naming conventions. They're indefensibly awful in every way.

This is generally good but it’s missing low speed (1.5 megabits/second), which is also under USB 1.1.

Great way of identifying the difference in types of USB

Where does TB5 come into all of this?

Why do we constantly change this?

What technological advance was not available x years ago to dream up usb 4?

We already know we will use the bandwith, why not dream up what will be the usb 8 spec in 20 years now and have everything working without change for 20 years?

nice work, thanks

[flagged]