Learn more about USB-C cable types
The topic of USB-C cables and connectors is quite confusing, and there are objective reasons for this. Many implementation options and nuances, coupled with not always conscientious manufacturers, bring confusion to the cable market. However, in the article I will show that everything in this matter is not so bad if you are ready to resort to a number of tricks and adjust your own expectations.
▍ Cable mess
You can have a whole bunch of USB-C cables that look the same on the outside, but you know they have different insides. And often there are no signs on them. Yes, it’s pretty bad, and you could even say that the situation is only getting worse.
I want to clarify right away that here we will only talk about USB-C “dad” to USB-C “dad” cables. Despite the popularity of cables like USB-A to USB-C, they are quite simple. In them, we have a USB 2.0 or 3.0 data transfer standard and support a current of no more than 2 A, and the USB-C connector is usually connected to the host with a voltage of 5 V, which is determined by a pull-up resistor. In addition, although visually cables like “Type-C to DisplayPort” may look like cables, in fact they are adapters stuffed with decent amount of electronics.
According to the specification alone, originally there was six types of USB-C to USB-C cables. Then them became eight. And now that number has reached twelve. And this is only in accordance with the specification, and there are still many third-party modifications. The good news is that usually most of these cables are quite suitable for simple tasks like charging devices and transferring data, and some specific cases of their use are quite rare.
Next, we will analyze the different types of cables, and you will understand that distinguishing them from each other is much easier than it might seem.
▍ Sorted by category
To begin with, there are two current carrying options for USB cables – 3 A and 5 A. 3 A is the minimum required for any cable, and 5 A is already supported as an option. Naturally, low-quality cables can fall short of up to 3 A, but this is a rare case. Last year, the USB-C group introduced EPR (Extended Power Range) technology, which raises the maximum voltage from 20 V to 48 V and requires improved isolation between the data and power pins. These are two additional categories, SPR (maximum 20V) and EPR (maximum 48V). However, 3 A EPR cables don’t exist, so this is a little less confusing than it might sound.
There are at least four options for data transfer speed. Previously, USB 2 and USB 3 cables with a Type-C connector were available to us, as well as a Thunderbolt interface. Now there is a new USB 3.1 standard that aims for higher speeds and needs faster cables. In addition, there are active USB-C cables that route the signal through redrivers or fiber optics to increase its transmission range. If you thought that cables use different wiring, which introduces additional variability both within the specification and outside of it, then, unfortunately, you were right.
The result is a three-by-four matrix representing the possible types of cables you have. Three rows in it indicate the current strength of 3 A, 5 A and EPR 5 A, and four columns indicate the transmission speed. In addition, there are many cables that fall out of the specification – for example, charging-only cables without 2.0 pins, which, of course, looks blasphemous from the point of view of technical requirements. Naturally, this can be bought both accidentally and intentionally. But how to determine the kind of those that you already have?
Let’s cut it down to a three-by-four space of options, leaving out the exceptions – over time, these weird cables will become less prominent as even low-end manufacturers eventually learn to follow the rules.
The undeniable advantage of such a range of all sorts of cables is the ability to buy exactly what will suit your needs, whether it’s a cheap $5 craft or a quality product for $40. However, 2.0 cables are thinner, lighter, and more flexible—because you definitely wouldn’t use Thunderbolt to charge your laptop on the go. In addition, USB-C has elements by which different cables can be distinguished. Next, I will talk about this in more detail.
▍ There is a computer in your cable…well, almost
When a power supply can deliver more than 3A of current through a cable, it will not do so immediately – it will first verify that the cable is capable of carrying that current and that the connected device can accept that current.
How specifically does it check the capabilities of the cable? Through reading his “E-Marker”. E-marker is a memory chip in the cable connector that encodes its capabilities and parameters, being connected to the SS channel for their transmission. This chip is required for all cables with speeds from USB 3 and current from 3 A. At the same time, a huge number of parameters can be encoded in the E-Marker, including even country code. Want to know more? I recommend reading technical description of the programmable microcircuit VL151which lists a lot of interesting information that can be obtained from a regular E-Marker.
If you wish, you can even buy these chips online and install them in your cables – for example,
. True, these chips can be flashed through I2C only three times. If you want to build your own 5A USB-C cables, you can also buy plugs with E-Markers already soldered in. Who knows, we might even see Doom on these chips soon.
▍ Self test cables
So, you can find out the capabilities of the cable by reading the E-Marker. Here, Linux users might think that this information should be available somewhere in
but, as you know, there is no such degree of support yet – the catalog
on my laptop, Framework 6.0.3 kernel is empty, even when a Type-C monitor is connected. Meanwhile there are
capable of reading information from the E-Marker.
If your cable does not have an E-Marker, then you can assume that it supports USB 2.0 transfer speed and 3A current, but hardly much more. In addition to the current carrying capacity of a cable, the E-Marker can tell you if it contains high-speed pairs, and which ones.
In a USB-C cable, there are usually either no such pairs at all, or there are four. Naturally, this is in addition to the obligatory pair of USB 2.0. However, there are exceptions – if you have a USB-A to USB-C cable with USB 3 support, then it will only have two pairs. Also, you will most likely find only two pairs in the USB-C to HDMI adapter with a built-in cable. Plus, from purely practical observations, I can say that I have a cable that came with the USB case – M.2 NVMe, and it also has only two pairs. It will work with USB 3.0, but will not fit DisplayPort or similar connectors – and it will not be long enough for such an application.
Want to check it out yourself? Luckily, you don’t have to cut the cable to do this. We have repeatedly dismantled testers for USB-C, and here
(English). These are open source solutions, and you can easily build such a device yourself. As an alternative, there are a whole bunch of ready-made ones on Tindie and Aliexpress. This fixture will not tell the difference between 20Gb/s and 40Gb/s cables, but it will help distinguish between USB 2.0 and 3.0 models.
In addition, the cables can be tested in vivo. If you are using a 100W charger and a laptop of similar power, you can easily check if your cable is providing 100W of power. To do this, just connect the charger and laptop through any cheap USB-C power meter and see if the current consumption exceeds 3A. A similar trick can be used when you have a bunch of cables and want to find out if they are up to USB 3 and higher. Here you will additionally need, for example, the same M.2 NVMe case with a USB 3 Type-C “mother” port.
In this case, you can perform the following quick test – connect the case to the laptop with a USB-C cable, then run
lsusb -twhich will show the connection speed (480 for USB 2 cables and 5000/10000 for USB 3). As a bonus, you can check to see if any of your cables fail the reversibility test – as this is still a problem.
▍ Completion of missing markings
Naturally, the manufacturer himself knows exactly the capabilities of his cables and their internal structure. But at the same time, he must accompany his products with markings, which in fact are quite rare. Sometimes the characteristics are indicated on the packages. So, if you haven’t thrown yours out yet, you can take a look at them or look at the product description in the online store. Let’s say you have an unlabeled cable and you’ve just defined its characteristics. How to be further?
Well, get out your nail polish bottles and follow recommendations [@_saljam]. Here is the color scheme for marking USB-C cables after you have figured out their parameters. One strip means 3 A, two stripes – 5 A. Orange is USB 2.0, blue is USB 3 20 Gb / s (Gen 1), green is USB 3 40 Gb / s (Gen 2), yellow is Thunderbolt. I especially like that the 5A Thunderbolt cables look like bees when using this design. Besides, [@_saljam] says that this scheme is quite suitable for the perception of color blind people.
Be that as it may, USB-C is on the mend. The responsible group introduced a new notation, which, by the way, was laughed at by many. Although this scheme is quite simple and not without meaning. If the cable supports 40 Gb/s, then it will have a 40 Gb/s logo on it. If it supports 240 W, then this characteristic will be indicated by the corresponding logo. If it implements support for both, then you will see both of these designations. You may not want to paint over these logos with varnish, but I’m sure you’ll come up with something.
▍ Integrated USB-C cables
You may have come across devices, such as docking stations, with built-in USB-C cables. This solution is an alternative to the standard female port and male to male cable. Fixed cables don’t fall under the same set of rules, and the electronics they use are much simpler, which is why they’re often installed in cheap devices.
Simply put, if you want to use high-speed lines on your device and embed a fixed cable in it, then you do not need to add a high-speed multiplexer to support two variants of plug orientation – in this case, the host is responsible for adjusting to one or another direction of its connection. Also, since the only possible CC line is hardwired, you’ll need one 5.1kΩ resistor instead of two, and you won’t need an E-Marker at all. If you add a “mother” port with high-speed lines to the docking station, then you can’t do without a multiplexer.
But under the terms of an agreement to sell well-equipped USB-C docking stations on Aliexpress for only $ 15, this option is not suitable. In this regard, many cheap devices are equipped with fixed cables, which both complicates and simplifies everything at the same time. The upside is that you no longer need to select the appropriate cable to connect the device, and it will certainly be optimally compliant with the standards, since it is very easy to implement such non-removable cables. The disadvantages include the limitation only to this cable built into the device. If it breaks, consider that the whole device breaks. Plus, you can’t increase it. Or can you?
Although I propose to postpone the issue of building up to another time, and with it the topic of USB-C cables that fall outside the requirements of the specification. Now I want to emphasize that the cables should be easily replaceable. If the cable suddenly ceased to be your friend or began to throw out oddities – stick a stigma on it, put it away so that there is no temptation to suddenly use it, and order a replacement. It’s better to have a few replacements. Here, as in the case of microUSB cables, replacement is the main way to get rid of the problems associated with them.