In July 2013 the USB Implementers Forum (consisting of 700 supporters) published the specifications for the up to 10GBit / s fast USB 3.1, also called SuperSpeedPlus (SS +). This specification also included the specification for USB 3.0 (SuperSpeed). In order to be able to distinguish between the two variants, the former USB 3.0 (with a maximum of 5 GBit / s) was renamed to USB 3.1 Generation 1. The SuperSpeedPlus variant (with a maximum of 10 GBit / s) is referred to as USB 3.1 Generation 2.
WHAT IS NEW?
The expansion of USB 3.0 (or USB 3.1 Gen. 1) to USB 3.1 Gen 2 covers almost all areas. The increased performance of USB 3.1 Gen. 2 is to let USB to make up for competing interfaces such as Thunderbolt, DisplayPort and MHL / SuperMHL or even overtake.
The new features that are of interest to the consumer are:
The data rate is increased from 5 GBit / s (SuperSpeed) to 10 GBit / s (SuperSpeedPlus / SS +). Thus, for the first time uncompressed UHD video signals, e.g. From a camera to a monitor, via USB.
The new Power Management USB Power Delivery 2.0 (USB PD 2.0) is introduced. The maximum allowed charging current is increased from 3 A to 5 A. The charging voltage can be up to 20 V. This means that devices with a power consumption of up to 100 W can also be supplied via a USB 3.1 cable. A sophisticated communication method can be used to determine what is connected to a device and how much charging or operating current / voltage is permissible.
The increased data rates and also the permissible high currents can not be realized via the conventional USB connectors. Therefore, a new connector type, the USB Type-C (also USB-C) is introduced. At the same time, the USB Type C connector will put an end to the mess, because USB Type-C can guarantee the widest compatibility for all USB variants as well as other (“alternative”) interfaces such as HDMI, MHL and DisplayPort , Because even Apple and Google now incorporate USB Type-C as the only physical connector into their devices, USB Type-C has the potential to become a universal connector.
TECHNICAL DESCRIPTION USB 3.1 GEN. 2
From SuperSpeed to SuperSpeed +
For a consumer, the changes in the protocols that control the flow of data are invisible. Here are the most important:
USB 3.1 Gen. 2 brings changes in all levels of host (source) and device (device, sink) and hubs in between. As existing software (drivers, etc.) is not to be modified, a hardware-oriented signaling mechanism has been implemented, which can be used to negotiate low-bandwidth bandwidths, energy parameters, etc. without affecting SuperSpeed communication. The new cables CC and SBU are described in chapter 3.2 and chapter 4.3.
To increase the nominal data rate from 5 GBit / s to 10 GBit / s, the clock is doubled and another line code is used:
A Gen. 1 Transmitter in the physical layer receives 8-bit data (data and control characters) from the higher protocol layers and scrambles these data to reduce electromagnetic interference (EMC). The scrambled 8-bit data is then recoded and transmitted into 10-bit data (symbols). A band width spreads the EMV again.
A receiver recovers the 8b / 10b encoded bitstream from the differential voltage, adds 10-bit data to each other, decodes and descrambles it. The resulting 8-bit data is passed to the higher protocol layers for further processing. The nominal data rate is 5 Gbps. The conversion from 8-bit to 10-bit per symbol produces a 20% overhead.
A Gen. 2 transmitter, however, uses a 128-bit or 16-symbol-long code group. This data block is preceded by a 4-bit block identifier. This construct is referred to as a 128b / 132b block. By contrasting with Gen. 1 greatly lengthened code groups, the overhead for the conversion from 20% at 8b / 10b to slightly more than 3% at 128b / 132b.
USB Gen. 1 knows only one class (type 1) of connection types. Herein, Between isochronous, periodic and transactional traffic. USB Gen. 2 adds a new class. This type 2 is only for asynchronous data packets. Thus, packets of type 1 can be prioritized higher in order to ensure an adequate bandwidth for the time-critical isochronous data traffic.
The new device class “Billboard Device” has been added to the USB-2 device classes (Device Classes). The Billboard class is a caseback scenario when no alternative connection between two USB devices can be established.
TECHNICAL DESCRIPTION USB TYPE-C
3.1 USB TYPE-C CONNECTOR
The most striking feature of USB 3.1 Gen. 2 is the new verb The most striking feature of USB 3.1 Gen. 2 is the new connector USB Type-C. The new connector for USB must match the current and future generations of products:
Narrow and flat design to fit the connector to mobile devices.
No type division into A (for hosts such as PCs or laptops) and B (for connected devices such as printers, smartphones, digital cameras and other accessories).
A standard cable has the same connectors on both ends.
Twist-proof, a plug can be plugged into a port in both directions.
Special USB Type C cables must also be connected to alternative interfaces such as DisplayPort or Thunderbolt.
The connector must be able to handle a charging power of up to 100 W (5 A at 20 V).
In order to meet the flat dimensions of modern mobile devices, the 2.56 x 8.34 mm USB C connector is even smaller than the micro USB connectors used in USB 3.1 Gen 1. In order to be able to reliably transmit high current and high data rates via such a small connector, the mechanical and electrical design of the connectors is quite complex.
Internal electrical connections distribute the current from VBUS to four contacts. The same is true for ground GND. The USB C connector has a ground plate between the rows of contacts, which is connected to the two side holding clamps. When inserting into the USB C socket, the holding clips of the plug snap into the side recesses of the middle ground plate of the socket. This creates a solid mechanical and electrical (mass) connection.
The USB-C connectors have two rows of 12 contacts each. C-connectors and C-connectors are horizontal and vertical mirror-symmetrical. Thus, a plug can be inserted into a Type C socket in two positions. Since a standard USB Type C cable always has a Type C connector at both ends, a cable can not be inserted incorrectly
The durability should be> 10.00 plug-in cycles.
3.2 SIGNALS IN A USB 3.1 GEN. 2 CONNECTION
The signals in a USB 3.1 connection can be divided into five groups: SuperSpeed link, USB 2.0 link, configuration, auxiliary signals and power.
The SuperSpeed link consists of two pairs of shielded twisted pair or coaxial cables. On each pair of lines, a symmetrical signal is transmitted in only one direction (= dual simplex method). The signal is provided with a 128b / 132b line code.
USB 2 link
The USB2 link provides compatibility with the old USB2 interface. The link is designed as a simple, shielded twisted-pair cable pair. The data are transmitted using the half-duplex method.
Configuration Channel / VCONN
Depending on the orientation of the plug in the socket, the pins A5 and B5 can alternately take over the function of the Configuration Channel (CC) or the VCONN. Via the configuration channel (CC) the plugging of a cable and the orientation of the plug are detected by the CC logic. VCONN then supplies an operating voltage for electronically marked cables. This allows the port processors and the chips in the cables to exchange SOP * messages and assign the roles in the system to each other.
The CC1 / CC2 cables have a minimum cross-section of 32 AWG (approx. 0.03 mm2).
Two lines for sideband use and for the transmission of analog audio signals. See also chapter 4.3 “The auxiliary signals SBU1 and SBU2”
A line that can transmit up to 5 A charging current. Cross section approx. 20-28 AWG (approx. 0.08-0.52 mm2)
Mass, one or two tinned leads. Cross-section approx. 20-28 AWG (approx. 0.08-0.52 mm2)
3.3 Construction of the cable
The specification of USB 3.1 Gen. 2 provides three types of USB Type-C cables. Depending on the cable type, a USB-C cable can have between 5 and 18 lines. A distinction must be made between two data bus systems, the lines for sideband transmission and the lines for current and voltage supply. Depending on the type of cable, the cable diameter is approx. 4-6 mm
3.4 USB TYPE C CABLE VARIANTS AND TYPE
In the USB 3.1 standard, only two pure USB Type C cables are provided: the Full Featured Cable and the USB 2.0 Type C cable. In addition, cables are allowed which have only one USB Type C connector. The other end of the cable must then be firmly connected to a device (Captive Cable Assembly).
To enable interoperability between USB C-terminated products and older USB products, some mixed-mounted cables and adapters have been defined.
3.4.1 Full Featured Cable / Electrically marked cable
The “Full Featured Cable” has a USB-C connector at both ends. All data buses and signaling lines are duplicated because of the torsional reliability of the connectors. However, only one set of lines is currently used. The second signal cable set is only used when a plug is inserted through 180 ° (see also Fig. 3.18 and Fig. 3.19). For all Full Featured Cables, chips for electronic marking are integrated into one or both connectors. Full Featured Cables are available in several variants:
Signals that transfer data streams at several Gbit / s lose quality through long interconnects, lines and parasitic capacitances. In longer cables, signal conditioners can be integrated, which reprocess the SS + signal. The signal conditioner is an active module and must therefore be supplied with operating voltage via VCONN.
Passive cables are electronically marked cables without signal conditioners.
Configurable Active Cables
Active cables that can be configured (e.g., to control load currents) require at least one controller that allows SOP * communication with a USB port controller.
3.4.2 USB 2.0 TYPE C CABLE
A USB 2.0 Type-C cable has the same appearance as a USB 3.1 Type-C cable. However, not all contacts are wired. USB 2.0 Type C cables with a permissible charging current above 3 A must be marked electronically. The electronic marking (VCONN) is located on pin B5.
3.4.3 CABLES CONNECTED WITH MIXED PLUGS
To operate older USB devices (USB 1 to USB 3.1 Gen. 1) together with new USB 3.1 Gen. 2 devices, some standard mixing cables were allowed. Special resistors are installed in the USB Type-C connectors of these cables. On the basis of these characteristic resistors, the USB 3.1 Gen.2 port processor recognizes that an older USB device is connected and limits the permissible charging current accordingly.
Adapters are short cables, with one USB-C connector at one end and a coupler (Receptacle) at the other end. Adapters are used to directly connect USB devices such as memory sticks or USB hard disks.
The system functionality is not guaranteed when using these adapters together with other USB cables!
3.4.5 CABLE FOR ALTERNATIVE MODES
Alternate modes are non-USB protocols, which can be transferred via a USB Type C connection. The individual pins of the connectors are assigned to other functions. Potentially, this can be transmitted in MHL, HDMI, DisplayPort and Thunderbolt format. More in chapter 4.4: Alternative connection modes
3.5 USB TYPE-C PORTS AND PORT CONTROLLER
In order for two or more USB devices to work together, they must communicate and assign a function or “role” according to their properties. This communication takes place between the USB Type C interfaces, the ports. A port consists of the type C socket, the port controller, and a discrete or integrated switch matrix. USB Type C ports can occur in different configurations:
DFP / UFP (Downstream Facing Port / Upstream Facing Port)
Defines the position of the port in the USB topology. A DFP corresponds to the old USB A port / host / source, a UFP corresponds to the old USB B port / device / sink.
Source / Sink (Source / Sink)
Defines the current role of the port as current source or load (current sink). Similarly, a data transmitter is a data source and a receiver is a data sink.
DRP (Dual RolePower)
The port can be used as current source or load (current sink).
DRD (Dual Role Data)
The port can be either DFP or UFP.
The role of a port can be changed during operation. Also, a mixed operation, e.g. The parallel roles as a data source and as a sink (“sinking host”) is possible.
USB standard load current (hardware start)
If two USB devices are connected directly or via a cable, the maximum USB default charging current and the orientation of the C connectors must first be determined. Then the roles in the system can be negotiated. To find this lowest common denominator, all USB devices and Type-C cables are equipped with coding resistors on the lines of the Configuration Channel (CC). With their help, the devices and cables can recognize each other, purely on a hardware basis.
Detect connection status
A source / host is identified with the pullup resistors or constant current sources Rp. The impedance or the current from Rp show the sink how much charge current the source can supply. A sink is marked with a pull-down resistor Rd. The current through Rp and Rd generates a specific voltage drop, which is evaluated by the CC logic via CC.
For electronically marked cables, VCONN (the open CCx cable) is terminated in the connectors with 800 Ω each. A source recognizes that VCONN is needed to supply the chips in the connectors.
CC1 and CC2 can assume three impedances from the viewpoint of a source: open, Rd and Ra. From the combination of the applied impedances, the CC logic can detect whether something is connected to the port, what is connected and in which orientation.
Detection of connector orientation
USB Type C cables have the same connectors on both ends, which can be inserted into two positions due to their horizontal and vertical symmetry. In order for the signal paths to be switched correctly in the ports, their CC logic must be aware of the direction of the cable and the orientation of the connectors. For this purpose, the CC logic evaluates the levels of CC1 and CC2. Since the voltage drops to CC first by the load of Rd and increases to a higher value after the sink is supplied with operating voltage, the logic in the source CC and thus the orientation of the plug can be recognized. Fig. 3.18, Fig. 3.19 and Fig. 3.20 show the signal flow for various plug orientations and device types.
USB POWER DELIVERY 2.0 (USB PD 2)
If the USB of earlier generations was only a data interface over which one could also supply a limited supply voltage for a device, this has practically reversed. USB is the interface for operating voltage and charging current and can be found on chargers, in cars, aircraft and wall brackets. However, the high current requirement of many devices exceeds that for which USB was originally specified.
4.1 LOGICAL STRUCTURE OF USB POWER DELIVERY
USB PD promises maximum functionality through flexible operating voltages and charging currents. Higher voltages and currents (up to 100 W) are defined by profiles. Tensions and currents are negotiated by source and sink. Source, current and data direction are reversible.
Standard policies support pure hardware launches (start with 5 V on VBUS). A software interface then allows the support of more complex policies. Fig. 4.01 shows the logical basic structure of USB PD.