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USB Cheat Sheet (2022)

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Re: USB Cheat Sheet (2022)

#71

Post by crote »

Liftyee wrote: post #63
gblargg wrote: post #62

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.

The wires count seems to be the number of conductors in the cable (i.e. the number of wires you'll find if you cut a cable in half, including ground and power). It's true that the actual data is sent over a lower number of diffpairs. I suspect the shield is not included in the number of wires, since all USB cables have a shield (not sure if usb 3.0 has an extra return ground wire for high speed).

It still would't be right. Full-featured USB-C has 8x superspeed (tx1p, tx1n, rx1p, rx1n, tx2p, tx2n, rx2p, rx2n), 2x high-speed (dp, dn), 2x power (vbus, gnd), 2x SBU, 1x CC. That's 15 wires.

Re: USB Cheat Sheet (2022)

#74

Post by wat10000 »

floxy wrote: post #43

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

Well, obviously. What do you think the U stands for? When we make contact with aliens, we’ll find them using it too.

Re: USB Cheat Sheet (2022)

#76

Post by toast0 »

mistyvales wrote: post #8
Neywiny wrote: post #5

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.

PCI-E has had the same standard since its inception: 1.0, 2.0, 3.0, etc. USB has changed multiple times and has remained confusing for the vast majority of people. What was 3.0 is now not 3.0. Even 3.1 has changed. There is no reason to use this naming convention they currently have but for some reason they stick with it..

The problem with USB, is the revisions are all encompasing. So USB 2.0 includes the 1.5 Mbps and 12.0 Mbps modes from usb 1.x as well as the new 480 Mbps mode, so you could have a USB 2.0 device that only did 12 Mbps (high speed!). It might actually be your old usb 1.1 device with a new label.

PCI-e requires hosts and devices to be backwards compatible, but the interface speed is a required part of the spec. Nobody makes a PCI-E 2.0 device that only works with PCI-E 1.0 encodings/speeds, or anyway, it wouldn't be acceptable.

Re: USB Cheat Sheet (2022)

#77

Post by ProllyInfamous »

adrian_b wrote: post #58
ProllyInfamous wrote: post #35

Earlier quoted context omitted.

It wasn't until last year that I finally purchased my first USB-C device/cables – and after years of solid DisplayPort and Thunderbolt2 connections I absolutely hate USB-C (it's too delicate, physically) . Not until 2023 did I even have a computer newer than 2012, so I missed almost all of USB3's hayday — including nomenclature disputes — but the speeds sure are an improvement!

While USB Type C can be broken much more easily by brute force and it is more prone to accidental disconnects than Type A, the Type C connectors are guaranteed to survive much more cycles of plugging/unplugging than Type A connectors. Type A connectors are typically guaranteed only for around 1000 cycles, with some better connectors rated up to 1500 cycles and some worse connectors rated only for a few hundred cycles…

Thanks for the details on mating cycles – although I've never had a TypeA connector "fail" from mating cycles (and have some in daily use for decades). I've only used USB-C for about a year, but have already broken one (which completely disables the plug, unlike the sculptable TypeA).

>It is true however that you must handle Type C connectors much more delicately than Type A, otherwise you can break them before they are worn out by mating cycles.

I would suspect that on a large enough datasample, TypeA connectors will out-survive TypeC (durability-wise), for your above reasoning alone. Have you ever worked hardware techsupport in an academic environment (or have children, or wives, or husbands)?

----

As an electrician with tons of realworld experience resolving burned-up installations, I also doubt the 240W-rating™ across top-end USB-C connectors is safe (I know theoretically it is... just like all those burnt-up outlets I've replaced in the real world). If I breath on my main display's USB-C connector (Obviously USB-A could never approach these power ratings, but I suspect USB-C cannot either (in realworld == electric fires). I love & use PoE (via Cat5e/6): it has much lesser-rated ampacity (despite higher cross-sectional area of wire).

Re: USB Cheat Sheet (2022)

#79

Post by adrian_b »

Liftyee wrote: post #65
Neywiny wrote: post #5

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.

Out of curiosity, what do you use the higher 20gbps transfer speeds for? Video production? I use USB-C displays, but they run in DP Alt mode. I don't have many (any?) storage devices that can max out a 20gbps connection, and usually don't exceed 5gbps

Any external NVMe SSD from the last 7-8 years easily saturates a 20 Gbps connection, because already from that time the NVMe SSDs were able to saturate a 32 Gb/s PCIe 3.0 4-lane connection.

For at least 7-8 years I have been using USB external enclosures for M.2 Key-M NVMe SSDs, which always saturated whatever kind of USB port they were connected to, i.e. 5/10/20 Gb/s.

I do not remember when I have last used a SATA SSD, which is slower than 10 and 20 Gb/s USB, but I think that this was about a decade ago.

Re: USB Cheat Sheet (2022)

#80

Post by adrian_b »

Neywiny wrote: post #68
Liftyee wrote: post #65

Earlier quoted context omitted.

Out of curiosity, what do you use the higher 20gbps transfer speeds for? Video production? I use USB-C displays, but they run in DP Alt mode. I don't have many (any?) storage devices that can max out a 20gbps connection, and usually don't exceed 5gbps

This goes back to another point I've historically made which is that except for storage devices, pretty much nothing supports those speeds. I think there are some USB adapters that don't use alt mode and that can have some advantages on some hosts but usually that's a disadvantage. USB interface chips are, as far as I've seen, a Cypress/Infineon FX3 or a bit more rare FTDI FT600/FT601. I even talked with the FTDI guy…

Besides storage devices, i.e. external SSDs, which are very frequently used and they need a USB port as fast as possible, the other frequent application that needs the fastest USB ports is the use of USB Ethernet interfaces.
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