A Basic USB-C Primer

Over the last five years or so there has been a quiet take-over of the ports on laptops, phones, and other devices, as a variety of older ports as well as the familiar USB A and micro USB sockets have been replaced by the now-ubiquitous USB-C port. It’s a connector which can do so many things, so many in fact that it bears a handy explanation. The Electromagnetic Field 2022 hacker camp has been quietly uploading videos of its talks, and a recent one has [Tyler Ward] explaining the intricacies of the interface.

Many of you will be familiar with XKCD number 927 which makes a joke about proliferating connector standards, and it’s evident that USB-C is a rare case of a connector which bucks the trend of simply making another standard, and has instead created something with which it makes sense to replace what went before. We learn about the intricacies of inter-device communications and USB-PD, and the multiple high-speed connection  lanes shoehorned into it. That one small connector can plug into a laptop and provide power, USB peripherals including network, and display, is nothing short of amazing. Take a look at the video below the break, and if you’re interested in diving deeper, have a look at our colleague [Arya Voronova]’s USB-C for hackers series.

32 thoughts on “A Basic USB-C Primer

      1. Yupp, just don’t use cables which come with (cheap) gadgets. They often only have GND and VBUS connected.

        Just bought a USB cable tester and threw everything like that out.

        After all, all Anker and other name brand cables in my collection do exactly what they claim.

        1. Bad hacker hoarder! Those cables always can have some use :p not everything needs to charge @5amps and do 40gbit all the time. I actually try to charge my phone as slow as possible, as its better for the battery.

          1. While is nice that I can charge my phone really fast by ramming 30 watts into it, it does make it quite toasty. Even at 15 watts it gets warmer than I like.

            I prefer overnight charging on a basic dumb USB-A charger as well.

        2. I have some cables like that specifically for powering devices where I don’t trust whatever I’m plugging into. Also useful for plugging into a usb outlet in a car when you don’t want the car to mount your device as a drive ( Toyota for example)
          Reminds me, I need a pair of usb-c breakout connectors.

      2. Just looking for a cable that supports Displayport was a terrible experience. I ended up just searching for thunderbolt cables, cause they don’t get away with just USB2 and power. I don’t need every cable to support everything, as they get quite thick as well, but maybe a clear certification would have been nice.

    1. Reputable source of USB cable should meet the standards but there’s always the cheap stuff that might barely meet the requirement or not meet it at all. In US it is not uncommon for some fool to plug a 15 amp space heater into a $3 power extension cord and start a fire.

      I was looking for replacement C-C cable for my laptop, I had to be careful about what cable to get as 65w is a fair amount of power going through thin wires. Cheap junk might heat up and melt or spark a fire. Unfortunately some cheap and shady companies don’t follow the rules and will use cheapest and thinnest wire and label the cable as compliant to all USB 3.x or 4 standards. It’ll work for USB SSD, it might be OK for some smart phones but it might not be safe when you’re pulling around 20v 3A through 30AWG wires for laptops.

      Maybe someone can do some testing and find if there’s a way to test cheap no name cables for compliance and safety? Just having correct wiring on both ends and having valid PD included somewhere may not be enough to protect users from under-rated wires.

  1. I don’t even think the fly leg sized fingers inside are up to some pocket lint and grunge from your phone.
    The kitchen counter is no place for these cables ends as one breadcrumb is a spanner in the works.

  2. USB is not Universal, not Serial and not a Bus.
    It’s not universal because both the peripheral and the stack are hard to implement by low level hardware, even the low bandwidth modes and certainly the new modes. And to that the crappy voltage tolerance that exclude device that require 5 volts. You also need to purchase a VID/PID.
    It’s not purely serial, because there are exceptions to the serial protocol and also analog modes. This is why isolating USB at high bandwidth is very difficult to do compared to real serial (Ethernet, RS485, etc.).
    It’s not a bus, because you can connect only one device. You need a hub.

    Terrible tolerances on the 5V voltage line should never have been allowed.
    They should never have used resistorvalues for communication purposes.
    With hindsight they could have implemented something much more elegant and universal.

      1. I know you are sarcastic, but it’s still a valid point. If they had consulted more engineers like me (I’m an embedded engineer) we could have given valuable feedback that could have led to a more elegant standard. No standard is perfect, but USB is an absolute mess.
        The same is true for the EVSE standard. Also an abomination of a standard.

          1. I’d be willing to bet most of the folks involved in making USB-C spec hate it, there are too many competing bits this connector ‘has’ to do because there are too many companies with wildly different goals involved. The simple elegant solution that works for most of them can’t fly because somebody else demands this bodged on addition or that one, which then snowballs the whole thing into a mess that hopefully might work for everyone.

          2. I agree with Foldi-One that bureaucracy and conflicting needs led to a sub-optimal design.
            I’m not claiming to be more experienced or more intelligent than all of the experts involved. The lack of intelligence is not the cause of the problems with the standard. In fact it is probably the opposite. They wanted the technology to be too smart and too complicated.
            Just like with politics where millions of people vote out of many potential leaders and we somehow end up with a government that is the worst of both worlds.

          3. you are basically arguing that a dictatorship that makes a few people completely happy and everyone else miserable is better than a democratic compromise that makes most people mostly happy. Which is correct if you are the dictator …

          4. Very much not in favour of dictatorship as a concept. But there is a time when adding ever more voices and trying to make a single specification please them all just makes things worse for everyone not better.

            USB-C is a victim of having at least two major but very different crowds with needs that barely overlap at all wanting it to be their connector – those that demand huge power draw and massive data bandwidth, in effect the higher end computer market, and those that wouldn’t mind more than 5V@2A and USB2 data speeds, but don’t have the cooling or performance to handle that much more than that – the lower power stuff like phones and gadgets – the ones that don’t need PCIe altmodes, or such huge bandwidth because their tiny internal storage would be filled nearly immediately if it could actually run that fast in the first place.

            Split those two into separate standards with different connectors. Perhaps mandate some data compatibility so in the same way you can adapt the right M.2 keyings that have USB into a regular USB header or normal PCIe slot quite trivially you can adapt one to talk to the other if you need to.

    1. Given that tiny cheap microcontrollers can bit-bang low-speed USB stuff, it’s not too bad for hobbyists to connect to anymore. In fact, tiny cheap microcontrollers can also do higher USB speeds quite often. Of course, given the ubiquity of USB-serial chips, it’s also easy to just stick with serial. It’s just the highest USB speeds that will remain difficult to work with, whether you’re a hobbyist or a pro.

    1. My guess is improper grounding of your PC. The USB ground is shared by the ground of your PC and if your PC isn’t plugged into a grounded socket you get half the mains voltage on the PC ground.

    2. Grounded USB PSUs are quite rare, it’s not needed as the transformer inside provides isolation. However to reduce RF noise they add a capacitor across the transformer, and that leaks a tiny bit of current.

      If you measure it it’ll be about half mains and very low current, like 200uA. You shouldn’t be able to feel it unless you hold it while in the shower etc.

      Your PSU may not be using the correct filter capacitor (many cheap out on this) or more worrying may be insulation breakdown on the transformer (that kills people).

      Your iron should have a screw to add a ground lead, adding that’ll fix it. That’s mainly for ESD, but some parts probably won’t be happy with that seeing that voltage.

        1. I prefer my old school Hakko 936 when soldering in the shower, it has a grounded tip.

          But yeah, dodgy PSUs have killed a few people. Normally it’s fine, but they’re having a bath and pick up their phone… the metal case + wet hands (low resistance) + good path to ground…

          Happens with other equipment as well, I had a DVD player or something where I could feel the voltage when I touched the metal case.

          1. My ex-mother in law often gets electrocuted in thunder storms as she insists on sleeping next to the phone in case of an emergency. She called us up once “Help, I think I’ve been electrocuted!!”

    3. That small shock you feel could destroy sensitive components you may be soldering. Make sure your iron is grounded. Most likely you are using it with an ungrounded power supply and the iron needs a separate ground wire if you are soldering solid state electronic components.

  3. Not impressed with a USB-C charging port on my pixel 4a. It’s so worn out I’ll be trading the phone in soon because the connection is so intermittent. Sucks to connect the charger and come back to a nearly dead phone.

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