The New USB Type-C – Data, Power and Display in the Same Interface

Published 17-06-09 in category USB Type-C™ • Writer Juha Eskola

Testing the New USB Type-C Interface

The new USB Type-C interface is not introducing just another higher interface speed class, or a new connector. USB-C is enabling all this and additionally many revolutionary aspects of USB, an interface that many PC users know only from the handy memory sticks.

Aspect One: New Connector

The new small sized orientation free connector might be one of the key things driving the increased interest of USB-C in many portable device categories. In spite of the small size the new 24-pin connector includes several highly-valued features

  • Four differential high speed lanes (10 Gbits/s duplex maximum)
  • Compatible USB 2.0 interface
  • Four Vbus Cable Power connects and four Cable Ground connects
  • Two Connector Configuration connects, and
  • Two Secondary Bus connects

Unlike earlier USB versions in USB-C both “host” and “device” use the same connector.

Aspect Two: Mixing Roles

A USB-C interface can present itself either as a Downstream Facing Port (DFP, data host), an Upstream Facing Port (UFP, device) or a Dual Role Port. A Dual Role Port is able to transitions between the two roles depending on the requested data transaction type.

Also from power source or consume point of view a USB-C device can have different roles. It can be in a Power Source role, a Power Sink role as before, but the power role can be different than the adopted data role. Through Power Delivery contract the connected devices can in the middle of a session swap the power role in the event of e.g. low battery capacity or a new power supply plug-in.

Aspect Three: Connection Detection

Since both ends of a full-featured USB-C cable are similar, the connected devices need to detect the way the signals are plugged together using the Configuration Channel (CC lines) for this task. The source (DFP) detects the connection type by measuring the resistance connected to the lines and the device (UFP) detects the signal orientation by measuring the voltage provided by the source to one of the lines.

Aspect Four: Higher Power Delivery Capability

As mentioned above, two connected devices that support power role swap can flexibly define the direction of the power flow during the session. They can also indicate to each other which voltages they support and how much current they are able to source with each voltage. With a proper cable the power delivered can be as high as 5 A at 20 V.

The USB power feature like the previously mentioned features are downwards compatible. This ensures that USB 1 and USB 2 devices work as before when connected to a USB-C port.

Aspect Five: Alternate Modes

USB-C enables "tunneling" other interfaces within itself. Currently there are four Alternate Mode Partner Specifications: DisplayPort Alternate Mode, MHL Alternate Mode, Thunderbolt Alternate Mode and HDMI Alternate Mode. Other Alternate Modes like PCI Express and Base-T Ethernet are possible.

In alternate modes, some of the interface signals are getting a new purpose. Each Alternate Mode standard defines the details of e.g. how the interface signals will be shared between the Alternate Mode and the USB data. Basic features like Power Delivery keep operating normally alongside the Alternate Mode.

Aspect Six: Live Display Over USB-C

As an example, let us have a look on how one of the Alternate Modes: DisplayPort™ over USB-C is implemented. The needed signals quite nicely fit into their original purpose in USB-C.

DisplayPort main lane signaling already supports packetized data transmission used in the four high-speed lanes of USB-C. Based on the capabilities of the connected devices and the delivered video stream, DisplayPort can use either 2 or 4 of the USB-C differential high speed lanes for payload data transmission. DisplayPort AUX Channel is using the USB-C Sideband (SBU) signaling.

DisplayPort over USB-C offers the same performance and feature capabilities as a standard DisplayPort connection. DisplayPort over USB-C allows DisplayPort data rates to even increase, since the USB-C connector has unutilized higher data rate capabilities that will potentially be utilized in the future.

USB Type-C – A Testing Challenge

The new USB-C connection is providing very attractive new features for the user. At the same time, it is introducing a magnitude of items to test for a designer or a manufacturer. Even if we forget the R&D and compliance testing here and concentrate only on the functionality testing needed in production line, we still have many items to cover. Designing compact, but reliable Test Cases for all USB-C device roles will be a challenge.

  • Data Roles: DFP, UFP and DRP
  • Power Role: Power Source, Power Sink
  • Power Level Capability:
  • Default USB, 1.5 A, 3.0 A
  • Up to 5 A @ 20 V
  • Two cable orientations
  • Alternate modes:
  • DisplayPort Alt Mode Sink and Source

You Need an Experienced and Reliable Partner

For testing USB-C connected devices you will need a test equipment provider that has capabilities and a firm track record for dealing with technologies like USB-C. The complicity of the protocols and the failure modes provides a real challenge both in terms of technological knowledge and also in terms of development and implementation timing. An experienced partner can help you on both.

Unigraf, a Display Interface Expert

Unigraf is one of the worldwide leading companies in testing the functionality of digital display interfaces. Unigraf's DisplayPort test and analyze tools have gained an industry standard position amongst the designers and testers of DisplayPort connected devices. All major providers of graphic controllers or TVs and monitors are using Unigraf test tools in their laboratories or in their production.

USB-C Test Device

Unigraf's UCD-340 is the first integrated test equipment for analyzing DisplayPort™ over USB Type-C sinks and sources. UCD-340 features a flexible and robust way of testing video, audio and power delivery functions of USB C. The provided software enables user access to the vital parameters and controls needed when evaluating the various functions of the interface.

Please find more information about UCD-340 on Unigraf website

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