The Relationship Between USB4 and the USB Type-C Connector

The USB4 specification was released by USB Implementors Forum (USB-IF) in September 2019, and one of its most advanced capabilities is its ability to support speeds up to 40 Gbps. Reaching these rapid data transfer rates is possible as USB4 architecture is based on Intel’s Thunderbolt 3 protocol that is built on a USB Type-C connector. How does the USB Type-C connector contribute to the operability of the USB4 specification and its capabilities? We’ll discuss this more in depth.

About the USB Type-C Connector and USB4

USB Type-C is a connector type that was created to simplify the USB user experience and for more universal adoption by manufacturers and consumers. Its ability to support high data transfer speeds, high power levels, and a number of different applications makes it more versatile. These functionalities are possible due to the USB Type-C connector’s unique internal infrastructure.

The USB Type-C connector includes 24 pins, with 4 of the pins (TX1+, TX1-, RX1+, RX1-) making up one lane with two differential SuperSpeed pairs and another 4 pins (TX2+, TX2-, RX2+, RX2-) making up a second lane with an additional set of two differential SuperSpeed pairs. Depending on the USB specification and configuration, one or two of the lanes can be used to transfer USB data at a given speed. If both lanes are used, the cable can transfer the data unidirectionally twice as fast. USB4 is able to transmit data at 20 Gbps per lane, or 40 Gbps if both lanes are used to perform a two-lane operation. If not all the SuperSpeed pins are used for USB data transfer, Alternate Mode can be activated, which supports third party protocols including DisplayPort (DP).

USB Type-C receptacle with pin diagram

Image by Chindi.ap

Additionally, there are other pins within a Type-C connector that are mandatory for all specifications, including four high speed (D+/ D-) pins to support USB 2.0 transfer rates, four GND pins to support the cable ground, four VBUS pins to support the cable bus power, two CC (CC1, CC2) pins to support the configuration channel, and two SBU (SBU1, SBU2) pins to support sideband use, where SBU1 is mapped to SBTX and SBU2 is mapped to SBRX when operating in USB4.

Configuration Channel and USB Power Delivery Protocol in USB4

The configuration channel (CC) within a USB Type-C connector is vital to the USB4 specification. For one, the configuration channel within a Type-C cable allows the cable to establish the relationship of Source and Sink roles between two attached ports. Secondly, because a USB Type-C cable can be inserted in either orientation, this channel also allows the cable to detect plug orientation and twist connections to establish USB data bus routing. Thirdly, both VBUS and VCONN are discovered and configured using this channel. Fourthly, it is used determine the lane ordering of the SuperSpeed USB data signal pairs and establish the Configuration Lane for dual-lane operation for USB 3.2 and USB4 specifications. And lastly, the USB Power Delivery protocol that functions over the configuration channel also allows the USB device to discover and configure Alternate or Accessory modes, as well as discover and enter USB4 operation.

USB4 Discovery and Entry Process

What does the USB4 discovery and entry look like? Initially, this process looks very similar to the discovery and entry of all USB connections. This process first begins with the Configuration Channel Connection State Machines resolving the Source/Sink and initial data roles (Downstream Facing Port (DFP)/Upstream Facing Port (UFP)). Next, the VBUS and VCONN supply power and the USB Power Delivery protocol is used to establish the Explicit Power Contract between the port and partners.

When, and only when the power contract has been established, the USB4 discovery process can begin. USB Power Delivery Discover Identity is used by the DFP to identify port partner SOP and SOP’ capabilities. If both USB Type-C port partners are discovered to support USB4 operation, the DFP will issue a USB PD message to the cable and port partner to allow the entrance of USB4.

The UFP ID Header and VDO responses used to determine level of USB4 compatibility:

  • Product type (hub, peripheral)
  • Device capabilities
  • Alt Mode support
  • Device speed
  • Power requirements

Devices that don’t respond are not recognized as USB4-compatible, and if no USB4 functionality is discovered, USB Type-C will functionally default to USB 2.0 and USB 3.2 specifications.

USB4 Power Requirements

In regards to USB4’s power requirements, the USB4 operation requires that the VBUS power is provided using a USB Power Delivery Explicit Contract. A dual-lane active cable may consume up to 1.5 W of power from VCONN. For Source power requirements, a minimum of 7.5 W (5 V at 1.5 A) is required to be supplied on each port. For Sink power requirements, devices are only allowed up to 250 mA on VBUS when the Source advertises Default USB power prior to establishing a PD Explicit Contract. Additionally, devices are required to be capable of operating with a Source that only supplies 7.5 W of power.

Summary

The USB4 specification relies on the USB Type-C connector to perform many of its functions. The Type-C connector allows cables supporting USB4 to achieve 40 Gbps transfer speeds, maintain safe power transfers between devices, as well as the ability to discover and enter the USB4 operation in a secure manner.

Tools for the Development of USB Type-C

Total Phase offers a variety of tools to help USB developers debug and develop their USB Type-C applications. The USB Power Delivery Analyzer connects in-line between two Type-C devices, and non-intrusively captures all communication between on both the CC1 and CC2 signals. This tool is able to capture the PD negotiation for power, USB data roles, and DisplayPort, or other Type-C Alternate Modes. Total Phase also provides various USB protocol analyzers supporting a wide range of data transfer rates, including USB 1.0, USB 2.0, and USB 3.2 up to 5 Gbps. When used with the Data Center Software, users can easily monitor and debug USB traffic occurring on the bus in real time. Additionally, cable developers can comprehensively test USB Type-C cables using the Advanced Cable Tester v2. This tool tests for pin continuity, E-Marker verification, DCR resistance, and quality of signal.

For more information on how our tools can help with the development of USB Type-C, please contact us at sales@totalphase.com or schedule a demo below.

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