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DisplayPort Alternate Mode 2.0: USB4 (requiring USB-C) requires that hubs support DisplayPort 2.0 over a USB-C Alternate Mode. DisplayPort 2.0 can support 8K resolution at 60Hz with HDR10 color. [120] DisplayPort 2.0 can use up to 80 Gbit/s, which is double the amount available to USB data, because it sends all the data in one direction (to the monitor) and can thus use all eight data wires at once. [120] As of 2023, [update] USB consists of four generations of specifications: USB 1. x, USB 2.0, USB 3. x, and USB4. USB4 enhances the data transfer and power delivery functionality with USB-IF Announces USB Audio Device Class 3.0 Specification". Business Wire (Press release). Houston, Texas & Beaverton, Oregon. 27 September 2016. Archived from the original on 4 May 2018 . Retrieved 4 May 2018. Contrary to other functions – which use the multiplexing of high-speed links – USB 2.0 over USB-C utilizes its own differential pair of wires. Matt Elliot (11 March 2019). "USB 3.2 explained: Making sense of current and confusing USB standards". CNET. Archived from the original on 7 July 2021 . Retrieved 26 July 2022.
USB signals are transmitted using differential signaling on twisted-pair data wires with 90 Ω ± 15% characteristic impedance. [93] USB 2.0 and earlier specifications define a single pair in half-duplex (HDx). USB 3.0 and later specifications define one dedicated pair for USB 2.0 compatibility and two or four pairs for data transfer: two pairs in full-duplex (FDx) for single lane variants require SuperSpeed connectors; four pairs in full-duplex for two lane (×2) variants require USB-C connectors. USB4 Gen 4 requires the use of all four pairs but allow for asymmetrical pairs configuration, [94] in this case one lane is used for the upstream data and the other three for the downstream data or vice-versa. USB4 Gen 4 use pulse amplitude modulation on 3 levels, providing a trit of information every baud transmitted, the transmission frequency of 12.8GHz translate to a transmission rate of 25.6 GBd [95] and the 11-bit–to–7-trit translation provides a theoretical maximum transmission speed just over 40.2 Gbit/s. [96] Operation mode Thunderbolt 3 uses USB-C cables; the USB4 specification allows hosts and devices and requires hubs to support interoperability with the standard using the Thunderbolt 3 Alternate Mode. The Type-B plug: This plug has a near square cross-section with the top exterior corners beveled. As part of a removable cable, it inserts into an upstream port on a device, such as a printer. On some devices, the Type-B receptacle has no data connections, being used solely for accepting power from the upstream device. This two-connector-type scheme (A/B) prevents a user from accidentally creating a loop. [9] [10]USB cables exist with various combinations of plugs on each end of the cable, as displayed below in the USB cables matrix. The chipset and drivers used to implement USB and FireWire have a crucial impact on how much of the bandwidth prescribed by the specification is achieved in the real world, along with compatibility with peripherals. [110] Ethernet [ edit ] High-speed USB2.0 hubs contain devices called transaction translators that convert between high-speed USB2.0 buses and full and low speed buses. There may be one translator per hub or per port. The limit to device power draw is stated in terms of a unit load which is 100mA for USB 2.0, or 150mA for SuperSpeed (i.e. USB 3. x) devices. Low-power devices may draw at most 1 unit load, and all devices must act as low-power devices before they are configured. A high-powered device must be configured, after which it may draw up to 5 unit loads (500mA), or 6 unit loads (900mA) for SuperSpeed devices, as specified in its configuration because the maximum power may not always be available from the upstream port. [43] [44] [45] [46] The connectors the USB committee specifies support a number of USB's underlying goals, and reflect lessons learned from the many connectors the computer industry has used. The female connector mounted on the host or device is called the receptacle, and the male connector attached to the cable is called the plug. [30] :2–5 – 2–6 The official USB specification documents also periodically define the term male to represent the plug, and female to represent the receptacle. [85] The legacy USB Type-A plug. This is one of many legacy types of USB connector.
The functionality of a USB device is defined by a class code sent to a USB host. This allows the host to load software modules for the device and to support new devices from different manufacturers. The Type-A plug. This plug has an elongated rectangular cross-section, inserts into a Type-A receptacle on a downstream port on a USB host or hub, and carries both power and data. Captive cables on USB devices, such as keyboards or mice, terminate with a Type-A plug. Because of the previous confusing naming schemes, USB-IF decided to change it once again. As of 2 September 2022, marketing names follow the syntax "USB xGbps", where x is the speed of transfer in Gb/s. [44] Overview of the updated names and logos can be seen in the adjacent table. Device Firmware Upgrade (DFU) is a vendor- and device-independent mechanism for upgrading the firmware of USB devices with improved versions provided by their manufacturers, offering (for example) a way to deploy firmware bug fixes. During the firmware upgrade operation, USB devices change their operating mode effectively becoming a PROM programmer. Any class of USB device can implement this capability by following the official DFU specifications. [58] [62] [63]
Please note:
A mix of USB specifications and their marketing names are being displayed because specifications are sometimes wrongly used as marketing names.) [ disputed(for: USB4 20Gbps does not exist; USB4 2×2 is not interchangeable with USB 3.2 2×2 as indicated by the logo; logos for USB 3.x and USB4 are different.) – discuss]
Upstream USB connectors supply power at a nominal 5 V DC via the V_BUS pin to downstream USB devices. On-The-Go Supplement 1.3 USB On-The-Go makes it possible for two USB devices to communicate with each other without requiring a separate USB host Axelson, Jan. "USB 3.0 Developers FAQ". Archived from the original on 20 December 2016 . Retrieved 20 October 2016. USB 3.1 - Type-C Host to Host". superuser.com. Archived from the original on 14 October 2021 . Retrieved 21 July 2021.The charging device identifies a charging port by non-data signaling on the D+ and D− terminals. A dedicated charging port places a resistance not exceeding 200Ω across the D+ and D− terminals. [50] :§ 1.4.7; table 5-3 USB3.1, released in July 2013 has two variants. The first one preserves USB3.0's SuperSpeed operation mode and is newly labeled USB3.1 Gen 1, [32] [33] and the second version introduces a new SuperSpeedPlus operation mode under the label of USB3.1 Gen 2 (marketed as SuperSpeed+ USB). SuperSpeed+ doubles the maximum data signaling rate to 10Gbit/s (later (USB 3.2) marketed as SuperSpeed USB 10Gbps), while reducing line encoding overhead to just 3% by changing the encoding scheme to 128b/132b. [32] [34] See also: USB mass storage device class, Disk enclosure, and External hard disk drive A flash drive, a typical USB mass-storage device An M.2 (2242) solid-state-drive ( SSD) connected into USB 3.0 adapter and connected to computer
Full Speed USB Maximum Theoretical Throughput". Microchip Technology Incorporated. 23 March 2021. Archived from the original on 26 March 2021 . Retrieved 23 March 2021. What Is the Maximum Length of a USB Cable?". Techwalla.com. Archived from the original on 1 December 2017 . Retrieved 18 November 2017. USB 3.2 Specification Language Usage Guidelines from USB-IF" (PDF). Archived (PDF) from the original on 3 November 2021 . Retrieved 4 September 2019. Low-speed (LS) and Full-speed (FS) modes use a single data wire pair, labeled D+ and D−, in half-duplex. Transmitted signal levels are 0.0–0.3 V for logical low, and 2.8–3.6 V for logical high level. The signal lines are not terminated. A stream pipe is a uni-directional pipe connected to a uni-directional endpoint that transfers data using an isochronous, [54] interrupt, or bulk transfer:SuperSpeed+ (SS+) uses a new coding scheme with an increased signaling rate (Gen 2×1 mode) and/or the additional lane of USB-C (Gen 1×2 and Gen 2×2 modes). The USB standard also provides multiple benefits for hardware manufacturers and software developers, specifically in the relative ease of implementation:
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