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An initial look at USB Type-C

Posted: 09 Feb 2015     Print Version  Bookmark and Share

Keywords:USB Type-C 

Observe the front row of four pins providing USB 1.x/2.0 backwards-compatibility; these are augmented by a second row of five pins that support USB 3.0 connectivity.

In July 2013, the USB 3.1 specification was released. By means of a new encoding scheme—coupled with enhanced, fully-backwards-compatible versions of the same cables and connectors as USB 3.0—USB 3.1 doubles the maximum bandwidth to 10 Gbps. This new transfer mode is officially referred to as "SuperSpeed USB 10 Gbps" or "SuperSpeed+" for short.

All of which means that we've now set the scene for USB Type-C to make its grand entrance (cue roll of drums and fanfare of trumpets)...

USB Type-C
There several different aspects to USB Type C, including the physical connector itself, a much more sophisticated power delivery scheme, and support for flexible new communication modes.

Let's start with the 24-pin connector, which is both small (3mm high and 8mm wide) and robust (it's rated for 10,000 mate/de-mate cycles).

Figure 6: 24-pin connector.

A few of the key features associated with USB Type-C cables and connectors are as follows:
 • The connector is non-polarized—it plugs in either way—no longer do we have to dork around trying to determine "Which side goes up?"
 • The connecter is small enough that the same connector can be used everywhere—on workstations, tablet computers, MP3 players, smartphones, digital cameras, etc.
 • Unlike the vast majority of other USB cables, Type-C cables have the same male connector on both ends—it's up to the things they are plugged into to "negotiate" with each other to determine who is in charge of doing what.
 • The specification supports data bandwidths up to 20 Gbps and facilitates alternate, non-USB, vendor-defined modes (you'll need the right type of cable to support these higher bandwidths and advanced modes as discussed below).
 • The specification supports power delivery of up to 100W for faster charging (you'll need the right type of cable to support the more advanced power delivery modes and higher power levels as discussed below).
 • In the case of the simpler power delivery and data transmission modes, passive (unintelligent) cables may be used. When it comes to the more advanced modes, intelligent cables will be required, where such cables contain an electronic ID that can inform the other elements in the system as to that cable's power capacity and the data bandwidths it can handle.

Now let's consider the pinout and primary signal assignments for the USB Type-C connector in a little more detail as illustrated below.

Figure 7: The pinout and primary signal assignments for the USB Type-C connector

The roles of the Vbus (power) and GND (ground) pins are reasonably self-explanatory, or so it would at first appear. In reality, things are a little more complex here than you might expect, but we'll return to this in a moment. First, we need to define a few terms, including Downstream-Facing Port (DFP), which we used to refer to as the host, and Upstream-Facing Port (UFP), which we used to think of as the peripheral device. There's also the concept of a Dual Role Port (DRP), which may be configured to act as a DFP or a UFP, and which may be dynamically switched back and forth between the two.

The D+ and D- pins are used to support legacy USB 2.0 devices. All that is required in this case is for the DFP to supply 5V on the Vbus pins and "Bob's your uncle" (or aunt, as the case may be).

Returning to the Vbus (power) pins, it used to be that the DFP always supplied power to the UFP; now, everything is up for grabs. Consider a USB Type-C-enabled tablet connected to a USB Type-C-enabled television, for example. In this case, the tablet may end up transmitting video data to the television, while the television ends up supplying power to the tablet. Alternatively, if a USB Type-C-enabled tablet were connected to a USB Type-C-enabled smartphone, the tablet may end up supplying the power while the smartphone returns video data for display.

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