The promising mess of usb-c – One cable that can do almost anything
During the course of the Computex fair last month, we gave a number of overviews of developments in the field of hardware, such as housings, cooling and especially RGB LEDs. What we skipped are motherboards. That has a number of reasons. The main one is the lack of the introduction of a new platform by AMD and Intel.
Although the latter has released its new Broadwell-E processors on the eve of Computex, they fit into the existing motherboards with X99 chipset. AMD, in turn, does not yet have a new platform, but several manufacturers confirmed that the AM4 generation will be introduced in the course of the third quarter. Unfortunately, June was still a bit too early to show those signs.
Although Broadwell does not bring a new socket, many manufacturers have refreshed their motherboard offerings with the arrival of the new processors. Many of those boards have a USB type-C connector on board, but that is by no means always only intended for USB data connections. And with countless peripherals that have the same plug, it’s time to get some clarity. Like last year , we made an appointment with chairman Jeff Ravencraft of the USB Implementers Forum to get a picture of the current state of affairs.
USB type c vs USB 3.1 gen 1 and gen 2
Last year, when the organization behind the introduction of the USB standard introduced the type-C connector and USB 3.1, there was quite a bit of confusion. On the one hand, the idea seemed to exist that only USB 3.1 could have a reversible type-c plug, on the other hand it was not entirely clear what that plug could do.
When the USB 3.1 standard also swallowed up the USB 3.0 standard in the course of the year and the former distinction between USB 3.0 and USB 3.1 became a lot more unclear, the confusion was almost complete. The old 3.0 standard became USB 3.1 Gen 1 and the former 3.1 standard became known as USB 3.1 Gen 2.
This gives us the following USB standards:
| USB version | Speed | encryption | Connectors |
|---|---|---|---|
| USB 2.0 (including USB 1.0 and 1.1) | up to 480 Mbit/s | 8/10bit | Type a, b, mini, micro, c |
| Usb 3.1 gen 1 | up to 5 Gbit/s | 8/10bit | Type a, b, mini, micro, c |
| Usb 3.1 gen 2 | up to 10 Gbit/s | 128/130bit | Type a, b, mini, micro, c |
The big difference between ‘3.1 gen 1’ and ‘3.1 gen 2’, which are called stiff 3.0 and 3.1 by many manufacturers to make it easier, is therefore not the plug. It’s the speed, the encryption, the security and the way two devices ‘negotiate’ the speed that make the difference. The type c connector can just as easily be used for 3.1 gen 1, or even usb 2.0 ports.
power delivery
Are we there then? No, because there is also an optional Power Delivery protocol to implement, PD for short. When implemented, the payload, or power supply, can be controlled and varied as needed. As icing on the cake, a new standard for charging was introduced almost simultaneously with USB 3.1 and the introduction of the type-C connector: the power delivery standard with no fewer than five levels. It prescribes different currents and different voltages, with 100W as the maximum. The powers are ‘negotiated’ between two devices, whereby the chip in the cable must also support the profile. There are five profiles, with powers from 0.5 to 100W and five voltages that can be negotiated. A sixth, 0 profile is reserved and not used.
| PD Profile | 5V C | 5V P | 9V C | 9V P | 12V C | 12V P | 15V C | 15V P | 20V C | 20V P |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 0.1A-3A | 0.5W-5W | note | note | note | note | ||||
| 2 | 3A | 15W | 1.7A-3A | 15.3W-27W | 1.5A | 18W | ||||
| 3 | 3A | 27W | 3A | 36W | 1.8A-3A | 27W-45W | ||||
| 4 | 3A | 45W | 2.25A – 3A | 45W-60W | ||||||
| 5 | 5A | 60W | 3A-5A | 60W-100W | ||||||
Revisions 2 and 3 of the Usb Power Delivery specification, with voltages above 5V, require a type c connector. Over a regular USB cable with a or b connectors, the current at 5V is basically limited to 2A and the 9V and 15V levels are not supported. Client and host negotiate over a data channel over a type c cable. Just as a type-c connector is not reserved for USB 3.1 Gen 2, PD is not exclusive to USB 3.1 Gen 2. USB 2.0 and 3.0 (or 3.1 Gen 1) cables can also use PD. However, the cables must be PD-aware and a micro connector can only support up to 60W. Incidentally, an ordinary cable can also deliver 25W, at 5V, via Battery Charging 1.2 profiles, but that falls outside the PD spec.
To prevent damage to client and host, or when the cable used is not PD-aware, a safe voltage and current is reverted. The devices then get stuck at 5V and 1.5A, good for 7.5W. By the way, the connection is initiated at 5V and 2A.
A revision 3 of the PD protocol has now also been published, which is identical to revision 2, with the main difference that authentication has now also been implemented. This should, among other things, prevent cables or chargers from advertising incorrect options and causing damage. Think, for example, of cables that cannot handle 5A and pose a fire hazard or a charger that tries to send too much current to a device and damages that device.
Enter thunderbolt
If that was already complicated, it will not surprise you that it can be a step worse. Last year, some companies, such as Gigabyte, advertised their USB ports that were twice as fast as those of competitors: 20Gbit/s. However, there is no USB standard that supports that. The trick? Those companies soldered Thunderbolt 2 chips onto their circuit boards, a standard that also uses the Type-C connector, but for Thunderbolt, and can also handle USB. Not only data can be sent via a Thunderbolt connection, such as via USB, but also video streams via DisplayPort, PCI-Express and network data.
This year we see a repetition of moves. Many motherboards come out with a ‘usb 3.1 type c’ connector that is not powered by a usb controller, but by an Alpine Ridge controller, better known as thunderbolt 3. Besides the advantage of several interfaces over the same connector, such as displayport , usb data and network, you can also use the different power profiles . One connector that replaces all others.
We see the thunderbolt implementation of the type c connector on motherboards with the designation 40Gbit / s; that’s how fast the thunderbolt 3 version has become. External housings for video cards, for example for laptops, also use PCI-Express over Thunderbolt, connected via a type-C connector. Many docks for laptops, with outputs for an additional monitor, a network port, a pair of USB ports, and a type-c connector for charging, use thunderbolt that connects through type-c connectors.
Alternate Modes
Thunderbolt is not the only multidisciplinary trick that the type c plug knows. Next to thunderbolt.
the type c standard includes various ‘Alternate Modes’, allowing not only USB traffic, but also video data and other protocols to be transported over the cable. Thunderbolt is one of the Alternate Modes of the type c connector. Two other alternatives are displayport, so that dvi and hdmi can be used over the cable, and mhl, which is especially useful for telephones. However, PCI express lanes, useful for external video cards for laptops, and Ethernet signals are also possible. The big advantage is that you have a plug and cable that can supply all data plus power for peripherals. For many peripherals, the cheaper and slightly slower USB 3.1 transfer in combination with power delivery is sufficient, but the same cable can therefore be used to drive an external video card or to make a laptop dock.
In fact, there are three major standards that work together to form a universal cable: usb 3.1 for data transfer, the power delivery specification, so that devices can be powered, and of course the type-c connector, which the previous two use and which is also suitable for video and other interfaces.