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USB, short for Universal Serial Bus, is an industry standard that was developed to define cables, connectors and protocols for connection, communication, and power supply between personal computers and their peripheral devices. [3] USB
USB
was designed to standardize the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electric power. It has largely replaced interfaces such as serial ports and parallel ports, and has become commonplace on a wide range of devices. USB
USB
connectors have replaced other types for battery chargers of portable devices. Released in 1996, the USB
USB
standard is currently maintained by the USB Implementers Forum ( USB
USB
IF).

Contents

1 Overview

1.1 Objectives 1.2 Limitations

2 History

2.1 Version history

2.1.1 Release versions 2.1.2 Power related specifications

2.2 USB
USB
1.x 2.3 USB
USB
2.0 2.4 USB
USB
3.x

3 System design 4 Device classes

4.1 USB
USB
mass storage / USB
USB
drive 4.2 Media Transfer Protocol 4.3 Human interface devices 4.4 Device Firmware
Firmware
Upgrade

5 Connectors

5.1 Connector properties

5.1.1 Durability 5.1.2 Compatibility

5.2 Connector types

5.2.1 Standard connectors 5.2.2 Mini connectors 5.2.3 Micro connectors

5.2.3.1 OMTP standard

5.2.4 USB 3.0
USB 3.0
connectors and backward compatibility 5.2.5 USB On-The-Go
USB On-The-Go
connectors 5.2.6 USB-C 5.2.7 Host and device interface receptacles

5.3 Pinouts

5.3.1 Proprietary connectors and formats

5.4 Colors

6 Cabling 7 Power

7.1 USB
USB
Battery Charging

7.1.1 Accessory charging adaptors (ACA)

7.2 Power Delivery (PD) 7.3 Sleep-and-charge ports 7.4 Mobile device charger standards

7.4.1 In China 7.4.2 OMTP/GSMA Universal Charging Solution 7.4.3 EU smartphone power supply standard

7.5 Non-standard devices 7.6 PoweredUSB

8 Signaling ( USB
USB
PHY)

8.1 Signaling rate (transmission rate)

8.1.1 Transaction latency

8.2 Electrical specification 8.3 Signaling state

8.3.1 Line transition state 8.3.2 Line state (covering USB 1.x and 2.x)

8.4 Transmission

8.4.1 Transmission example on a USB 1.1 full-speed device

8.5 USB 2.0 speed negotiation 8.6 USB 3.0

9 Protocol layer

9.1 Handshake packets 9.2 Token packets

9.2.1 OUT, IN, SETUP, and PING token packets 9.2.2 SOF: Start-of-frame 9.2.3 SSPLIT and CSPLIT: Start-split transaction and complete split transaction

9.3 Data packets 9.4 PRE packet (tells hubs to temporarily switch to low speed mode)

10 Transaction

10.1 OUT transaction 10.2 IN transaction 10.3 SETUP transaction

10.3.1 Setup packet

10.4 Control transfer exchange

11 Audio streaming 12 Comparisons with other connection methods

12.1 FireWire 12.2 Ethernet 12.3 MIDI 12.4 eSATA/eSATAp 12.5 Thunderbolt

13 Interoperability 14 Related standards 15 See also 16 References 17 Further reading 18 External links

Overview[edit] Objectives[edit] The Universal Serial Bus was developed to simplify and improve the interface between personal computers and peripheral devices, when compared with previously existing standard or ad-hoc proprietary interfaces. [4] From the computer user's perspective, the USB
USB
interface improved ease of use in several ways. The USB
USB
interface is self-configuring, so the user need not adjust settings on the device and interface for speed or data format, or configure interrupts, input/output addresses, or direct memory access channels. [5] USB
USB
connectors are standardized at the host, so any peripheral can use any available socket. USB
USB
takes full advantage of the additional processing power that can be economically put into peripheral devices so that they can manage themselves; USB
USB
devices often do not have user-adjustable interface settings. The USB
USB
interface is "hot pluggable", meaning devices can be exchanged without rebooting the host computer. Small devices can be powered directly from the USB
USB
interface, displacing extra power supply cables. Because use of the USB
USB
logos is only permitted after compliance testing, the user can have confidence that a USB
USB
device will work as expected without extensive interaction with settings and configuration; the USB
USB
interface defines protocols for recovery from common errors, improving reliability over previous interfaces. [4] Installation of a device relying on the USB
USB
standard requires minimal operator action. When a device is plugged into a port on a running personal computer system, it is either entirely automatically configured using existing device drivers, or the system prompts the user to locate a driver which is then installed and configured automatically. For hardware manufacturers and software developers, the USB
USB
standard eliminates the requirement to develop proprietary interfaces to new peripherals. The wide range of transfer speeds available from a USB interface suits devices ranging from keyboards and mice up to streaming video interfaces. A USB
USB
interface can be designed to provide the best available latency for time-critical functions, or can be set up to do background transfers of bulk data with little impact on system resources. The USB
USB
interface is generalized with no signal lines dedicated to only one function of one device. [4] Limitations[edit] USB
USB
cables are limited in length, as the standard was meant to connect to peripherals on the same table-top, not between rooms or between buildings. However, a USB
USB
port can be connected to a gateway that accesses distant devices. USB
USB
has a strict "tree" topology and "master-slave" protocol for addressing peripheral devices; peripheral devices cannot interact with one another except via the host, and two hosts cannot communicate over their USB
USB
ports directly. Some extension to this limitation is possible through " USB
USB
On The Go". A host cannot "broadcast" signals to all peripherals at once, each must be addressed individually. Some very high speed peripheral devices require sustained speeds not available in the USB
USB
standard. [4] While converters exist between certain "legacy" interfaces and USB, they may not provide full implementation of the legacy hardware; for example, a USB
USB
to parallel port converter may work well with a printer, but not with a scanner that requires bi-directional use of the data pins. For a product developer, use of USB
USB
requires implementation of a complex protocol and implies an "intelligent" controller in the peripheral device. Developers of USB
USB
devices intended for public sale generally must obtain a USB
USB
ID which requires a fee paid to the Implementers' Forum. Developers of products that use the USB specification must sign an agreement with Implementer's Forum. Use of the USB
USB
logos on the product require annual fees and membership in the organization. [4] History[edit]

The basic USB
USB
trident logo[6]

USB
USB
logo on the head of a standard A plug

A group of seven companies began the development of USB
USB
in 1994: Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel.[7] The goal was to make it fundamentally easier to connect external devices to PCs by replacing the multitude of connectors at the back of PCs, addressing the usability issues of existing interfaces, and simplifying software configuration of all devices connected to USB, as well as permitting greater data rates for external devices. A team including Ajay Bhatt worked on the standard at Intel;[8][9] the first integrated circuits supporting USB
USB
were produced by Intel
Intel
in 1995.[10] The original USB 1.0 specification, which was introduced in January 1996, defined data transfer rates of 1.5  Mbit/s Low Speed and 12  Mbit/s Full Speed.[10] Microsoft
Microsoft
Windows 95, OSR 2.1 provided OEM support for the devices. The first widely used version of USB
USB
was 1.1, which was released in September 1998. The 12 Mbit/s data rate was intended for higher-speed devices such as disk drives, and the lower 1.5  Mbit/s rate for low data rate devices such as joysticks.[11] Apple Inc.'s iMac was the first mainstream product with USB
USB
and the iMac's success popularized USB
USB
itself.[12] Following Apple's design decision to remove all legacy ports from the iMac, many PC manufacturers began building legacy-free PCs, which led to the broader PC market using USB
USB
as a standard.[13][14][15] The USB 2.0 specification was released in April 2000 and was ratified by the USB Implementers Forum (USB-IF) at the end of 2001. Hewlett-Packard, Intel, Lucent Technologies
Lucent Technologies
(now Nokia), NEC, and Philips
Philips
jointly led the initiative to develop a higher data transfer rate, with the resulting specification achieving 480 Mbit/s, 40 times as fast as the original USB
USB
1.1 specification. The USB 3.0
USB 3.0
specification was published on 12 November 2008. Its main goals were to increase the data transfer rate (up to 5 Gbit/s), decrease power consumption, increase power output, and be backward compatible with USB
USB
2.0.[16] USB 3.0
USB 3.0
includes a new, higher speed bus called SuperSpeed
SuperSpeed
in parallel with the USB
USB
2.0 bus.[17] For this reason, the new version is also called SuperSpeed.[18] The first USB 3.0 equipped devices were presented in January 2010.[18][19] As of 2008[update], approximately 6 billion USB
USB
ports and interfaces were in the global marketplace, and about 2 billion were being sold each year.[20] The USB 3.1 specification was published in July 2013. In December 2014, USB-IF submitted USB 3.1, USB
USB
Power Delivery 2.0 and USB
USB
Type-C specifications to the IEC (TC 100 – Audio, video and multimedia systems and equipment) for inclusion in the international standard IEC 62680 Universal Serial Bus interfaces for data and power, which is currently based on USB
USB
2.0.[21] The USB 3.2 specification was published in September 2017. Version history [edit] Release versions[edit]

Release name Release date Maximum transfer rate Note

USB 0.8 December 1994

Prerelease

USB 0.9 April 1995

Prerelease

USB 0.99 August 1995

Prerelease

USB 1.0-RC November 1995

Release Candidate

USB 1.0 January 1996 Full Speed (12 Mbit/s)

USB 1.1 August 1998 Full Speed (12 Mbit/s)[22]

USB 2.0 April 2000 High Speed (480 Mbit/s)

USB 3.0 November 2008 SuperSpeed
SuperSpeed
(5 Gbit/s) Also referred to as USB 3.1 Gen 1[23] and USB
USB
3.2 Gen 1x1

USB 3.1 July 2013 SuperSpeed+ (10 Gbit/s) Also referred to as USB 3.1 Gen 2 [23] and USB
USB
3.2 Gen 2x1

USB 3.2 September 2017 SuperSpeed+ (20 Gbit/s) Includes new USB 3.2 Gen 1x2 and USB 3.2 Gen 2x2 multi-link modes [24][not in citation given]

Power related specifications[edit]

Release name Release date Max. power Note

USB
USB
Battery Charging 1.0 2007-03-08 5 V, 1.5 A

USB
USB
Battery Charging 1.1 2009-04-15

USB
USB
Battery Charging 1.2 2010-12-07 5 V, 5 A

USB Power Delivery
USB Power Delivery
revision 1.0 (version 1.0) 2012-07-05 20 V, 5 A Using FSK protocol over bus power (VBUS)

USB Power Delivery
USB Power Delivery
revision 1.0 (version 1.3) 2014-03-11

USB
USB
Type-C 1.0 2014-08-11 5 V, 3 A New connector and cable specification

USB Power Delivery
USB Power Delivery
revision 2.0 (version 1.0) 2014-08-11 20 V, 5 A Using BMC protocol over communication channel (CC) on type-C cables.

USB
USB
Type-C 1.1 2015-04-03 5 V, 3 A

USB Power Delivery
USB Power Delivery
revision 2.0 (version 1.1) 2015-05-07 20 V, 5 A

USB Power Delivery
USB Power Delivery
revision 2.0 (version 1.2) 2016-03-25 20 V, 5 A

USB Power Delivery
USB Power Delivery
revision 3.0 (version 1.1) 2017-01-12 20 V, 5 A

USB
USB
1.x[edit] Released in January 1996, USB 1.0 specified data rates of 1.5  Mbit/s (Low Bandwidth or Low Speed) and 12  Mbit/s (Full Speed).[25] It did not allow for extension cables or pass-through monitors, due to timing and power limitations. Few USB
USB
devices made it to the market until USB 1.1 was released in August 1998. USB 1.1 was the earliest revision that was widely adopted and led to what Microsoft
Microsoft
designated the "Legacy-free PC".[12][13][14][15] Neither USB
USB
1.0 nor 1.1 specified a design for any connector smaller than the standard type A or type B. Though many designs for a miniaturised type B connector appeared on many peripherals, conformance to the USB
USB
1.x standard was fudged by treating peripherals that had miniature connectors as though they had a tethered connection (that is: no plug or socket at the peripheral end). There was no known miniature type A connector until USB
USB
2.0 (rev 1.01) introduced one. USB
USB
2.0[edit]

The Hi-Speed USB
USB
logo

A USB
USB
2.0 PCI expansion card

USB 2.0 was released in April 2000, adding a higher maximum signaling rate of 480  Mbit/s (High Speed or High Bandwidth), in addition to the USB 1.x Full Speed signaling rate of 12 Mbit/s. Due to bus access constraints, the effective throughput of the High Speed signaling rate is limited to 280  Mbit/s or 35 MB/s.[26] Modifications to the USB
USB
specification have been made via Engineering Change Notices (ECN). The most important of these ECNs are included into the USB
USB
2.0 specification package available from USB.org:[27] Some of the most significant items included in the change notices include:

Mini-A and Mini-B Connector Micro- USB
USB
Cables and Connectors Specification 1.01 InterChip USB Supplement On-The-Go
On-The-Go
Supplement 1.3 USB On-The-Go
USB On-The-Go
makes it possible for two USB devices to communicate with each other without requiring a separate USB
USB
host. Battery Charging Specification 1.1 Added support for dedicated chargers , host chargers behavior for devices with dead batteries. Battery Charging Specification 1.2:[28] with increased current of 1.5 A on charging ports for unconfigured devices, allowing High Speed communication while having a current up to 1.5 A and allowing a maximum current of 5 A. Link Power Management Addendum ECN which adds a sleep power state.

USB
USB
3.x[edit] Main article: USB
USB
3.0

The SuperSpeed
SuperSpeed
USB
USB
logo

The USB 3.0 specification was released on 12 November 2008, with its management transferring from USB 3.0 Promoter Group to the USB Implementers Forum (USB-IF), and announced on 17 November 2008 at the SuperSpeed
SuperSpeed
USB
USB
Developers Conference.[29] USB 3.0 adds a SuperSpeed
SuperSpeed
transfer mode, with associated backward compatible plugs, receptacles, and cables. SuperSpeed
SuperSpeed
plugs and receptacles are identified with a distinct logo and blue inserts in standard format receptacles. The SuperSpeed
SuperSpeed
mode provides a data signaling rate of 5.0 Gbit/s. However, due to the overhead incurred by 8b/10b encoding, the payload throughput is actually 4 Gbit/s, and the specification considers it reasonable to achieve about 3.2 Gbit/s (0.4 GB/s or 400 MB/s). Communication is full-duplex in SuperSpeed
SuperSpeed
transfer mode; earlier modes are half-duplex, arbitrated by the host.[30] Low-power and high-power devices remain operational with this standard, but devices using SuperSpeed
SuperSpeed
can take advantage of increased available current of between 150 mA and 900 mA, respectively.[31] USB 3.1, released in July 2013, preserves the existing SuperSpeed transfer rate under a new label USB
USB
3.1 Gen 1,[32][33] and introduces a new SuperSpeed+ transfer mode, USB
USB
3.1 Gen 2 with the maximum data signaling rate to 10 Gbit/s (1250 MB/s, twice the rate of USB 3.0), which reduces line encoding overhead to just 3% by changing the encoding scheme to 128b/132b[32][34][35] USB 3.2, released in September 2017, preserves existing USB
USB
3.1 SuperSpeed
SuperSpeed
and SuperSpeed+ data modes but introduces two new SuperSpeed+ transfer modes over the USB-C
USB-C
connector with data rates of 10 and 20 Gbit/s (1250 and 2500 MB/s). The increase in bandwidth is a result of multi-lane operation over existing wires that were intended for flip-flop capabilities of the Type-C connector.[36] System design[edit] A USB
USB
system consists of a host with one or more downstream ports, and multiple peripherals, forming a tiered-star topology. Additional USB hubs may be included, allowing up to five tiers. A USB
USB
host may have multiple controllers, each with one or more ports. Up to 127 devices may be connected to a single host controller.[37][38] USB
USB
devices are linked in series through hubs. The hub built into the host controller is the root hub. A USB
USB
device may consist of several logical sub-devices that are referred to as device functions. A composite device may provide several functions, for example, a webcam (video device function) with a built-in microphone (audio device function). An alternative to this is compound device, in which the host assigns each logical device a distinctive address and all logical devices connect to a built-in hub that connects to the physical USB
USB
cable.

USB
USB
endpoints reside on the connected device: the channels to the host are referred to as pipes

USB
USB
device communication is based on pipes (logical channels). A pipe is a connection from the host controller to a logical entity, found on a device, and named an endpoint. Because pipes correspond to endpoints, the terms are sometimes used interchangeably. A USB
USB
device could have up to 32 endpoints (16 IN, 16 OUT), though it is rare to have so many. An endpoint is defined and numbered by the device during initialization (the period after physical connection called "enumeration") and so is relatively permanent, whereas a pipe may be opened and closed. There are two types of pipe: stream and message. A message pipe is bi-directional and is used for control transfers. Message pipes are typically used for short, simple commands to the device, and a status response, used, for example, by the bus control pipe number 0. A stream pipe is a uni-directional pipe connected to a uni-directional endpoint that transfers data using an isochronous,[39] interrupt, or bulk transfer:

Isochronous transfers At some guaranteed data rate (often, but not necessarily, as fast as possible) but with possible data loss (e.g., realtime audio or video) Interrupt
Interrupt
transfers Devices that need guaranteed quick responses (bounded latency) such as pointing devices, mice, and keyboards Bulk transfers Large sporadic transfers using all remaining available bandwidth, but with no guarantees on bandwidth or latency (e.g., file transfers)

When a host starts a data transfer, it sends a TOKEN packet containing an endpoint specified with a tuple of (device_address, endpoint_number). If the transfer is from the host to the endpoint, the host sends an OUT packet (a specialization of a TOKEN packet) with the desired device address and endpoint number. If the data transfer is from the device to the host, the host sends an IN packet instead. If the destination endpoint is a uni-directional endpoint whose manufacturer's designated direction does not match the TOKEN packet (e.g. the manufacturer's designated direction is IN while the TOKEN packet is an OUT packet), the TOKEN packet is ignored. Otherwise, it is accepted and the data transaction can start. A bi-directional endpoint, on the other hand, accepts both IN and OUT packets.

Two USB 3.0 standard A sockets (left) and two USB 2.0 sockets (right) on a computer's front panel

Endpoints are grouped into interfaces and each interface is associated with a single device function. An exception to this is endpoint zero, which is used for device configuration and is not associated with any interface. A single device function composed of independently controlled interfaces is called a composite device. A composite device only has a single device address because the host only assigns a device address to a function. When a USB
USB
device is first connected to a USB
USB
host, the USB
USB
device enumeration process is started. The enumeration starts by sending a reset signal to the USB
USB
device. The data rate of the USB
USB
device is determined during the reset signaling. After reset, the USB
USB
device's information is read by the host and the device is assigned a unique 7-bit address. If the device is supported by the host, the device drivers needed for communicating with the device are loaded and the device is set to a configured state. If the USB
USB
host is restarted, the enumeration process is repeated for all connected devices. The host controller directs traffic flow to devices, so no USB
USB
device can transfer any data on the bus without an explicit request from the host controller. In USB 2.0, the host controller polls the bus for traffic, usually in a round-robin fashion. The throughput of each USB
USB
port is determined by the slower speed of either the USB
USB
port or the USB
USB
device connected to the port. High-speed USB 2.0 hubs contain devices called transaction translators that convert between high-speed USB 2.0 buses and full and low speed buses. There may be one translator per hub or per port. Because there are two separate controllers in each USB 3.0 host, USB 3.0 devices transmit and receive at USB 3.0 data rates regardless of USB 2.0 or earlier devices connected to that host. Operating data rates for earlier devices are set in the legacy manner. Device classes[edit] The functionality of a USB
USB
device is defined by a class code sent to a USB
USB
host. This allows the host to load software modules for the device and to support new devices from different manufacturers. Device classes include:[40]

Class Usage Description Examples, or exception

00h Device Unspecified[41] Device class is unspecified, interface descriptors are used to determine needed drivers

01h Interface Audio Speaker, microphone, sound card, MIDI

02h Both Communications and CDC Control Modem, Ethernet
Ethernet
adapter, Wi-Fi
Wi-Fi
adapter, RS232
RS232
serial adapter. Used together with class 0Ah (below)

03h Interface Human interface device (HID) Keyboard, mouse, joystick

05h Interface Physical Interface Device (PID) Force feedback joystick

06h Interface Image (PTP/MTP) Webcam, scanner

07h Interface Printer Laser printer, inkjet printer, CNC machine

08h Interface Mass storage (MSC or UMS) USB
USB
flash drive, memory card reader, digital audio player, digital camera, external drive

09h Device USB
USB
hub Full bandwidth hub

0Ah Interface CDC-Data Used together with class 02h (above)

0Bh Interface Smart Card USB
USB
smart card reader

0Dh Interface Content security Fingerprint reader

0Eh Interface Video Webcam

0Fh Interface Personal healthcare device class (PHDC) Pulse monitor (watch)

10h Interface Audio/Video (AV) Webcam, TV

11h Device Billboard Describes USB
USB
Type-C alternate modes supported by device

DCh Both Diagnostic Device USB
USB
compliance testing device

E0h Interface Wireless
Wireless
Controller Bluetooth
Bluetooth
adapter, Microsoft
Microsoft
RNDIS

EFh Both Miscellaneous ActiveSync
ActiveSync
device

FEh Interface Application-specific IrDA Bridge, Test & Measurement Class (USBTMC),[42] USB
USB
DFU (Device Firmware
Firmware
Upgrade)[43]

FFh Both Vendor-specific Indicates that a device needs vendor-specific drivers

USB
USB
mass storage / USB
USB
drive[edit]

A flash drive, a typical USB
USB
mass-storage device

Circuit board from a USB 3.0
USB 3.0
external 2.5-inch SATA
SATA
HDD enclosure

See also: USB
USB
mass storage device class, Disk enclosure, and External hard disk drive USB mass storage device class
USB mass storage device class
(MSC or UMS) standardizes connections to storage devices. At first intended for magnetic and optical drives, it has been extended to support flash drives. It has also been extended to support a wide variety of novel devices as many systems can be controlled with the familiar metaphor of file manipulation within directories. The process of making a novel device look like a familiar device is also known as extension. The ability to boot a write-locked SD card
SD card
with a USB adapter
USB adapter
is particularly advantageous for maintaining the integrity and non-corruptible, pristine state of the booting medium. Though most personal computers since mid-2004 can boot from USB
USB
mass storage devices, USB
USB
is not intended as a primary bus for a computer's internal storage. . However, USB
USB
has the advantage of allowing hot-swapping, making it useful for mobile peripherals, including drives of various kinds. First conceived and still used today for optical storage devices ( CD-RW
CD-RW
drives, DVD
DVD
drives, etc.), several manufacturers offer external portable USB
USB
hard disk drives, or empty enclosures for disk drives. These offer performance comparable to internal drives, limited by the current number and types of attached USB
USB
devices, and by the upper limit of the USB
USB
interface. Other competing standards for external drive connectivity include eSATA, ExpressCard, FireWire
FireWire
(IEEE 1394), and most recently Thunderbolt. Another use for USB
USB
mass storage devices is the portable execution of software applications (such as web browsers and VoIP
VoIP
clients) with no need to install them on the host computer.[44][45] Media Transfer Protocol[edit] See also: Picture Transfer Protocol Media Transfer Protocol (MTP) was designed by Microsoft
Microsoft
to give higher-level access to a device's filesystem than USB
USB
mass storage, at the level of files rather than disk blocks. It also has optional DRM features. MTP was designed for use with portable media players, but it has since been adopted as the primary storage access protocol of the Android operating system from the version 4.1 Jelly Bean as well as Windows Phone 8 (Windows Phone 7 devices had used the Zune protocol—an evolution of MTP). The primary reason for this is that MTP does not require exclusive access to the storage device the way UMS does, alleviating potential problems should an Android program request the storage while it is attached to a computer. The main drawback is that MTP is not as well supported outside of Windows operating systems. Human interface devices[edit] Main article: USB
USB
human interface device class Joysticks, keypads, tablets and other human-interface devices (HIDs) are also progressively[when?] migrating from MIDI, and PC game port connectors to USB.[citation needed] USB
USB
mice and keyboards can usually be used with older computers that have PS/2 connectors with the aid of a small USB-to-PS/2 adapter. For mice and keyboards with dual-protocol support, an adaptor that contains no logic circuitry may be used: the hardware in the USB keyboard or mouse is designed to detect whether it is connected to a USB
USB
or PS/2 port, and communicate using the appropriate protocol. Converters also exist that connect PS/2 keyboards and mice (usually one of each) to a USB
USB
port.[46] These devices present two HID endpoints to the system and use a microcontroller to perform bidirectional data translation between the two standards. Device Firmware
Firmware
Upgrade[edit] Device Firmware
Firmware
Upgrade (DFU) is a vendor- and device-independent mechanism for upgrading the firmware of USB
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
USB
devices change their operating mode effectively becoming a PROM programmer. Any class of USB
USB
device can implement this capability by following the official DFU specifications.[43][47][48] In addition to its intended legitimate purposes, DFU can also be exploited by uploading maliciously crafted firmware that causes USB devices to spoof various other device types; one such exploiting approach is known as BadUSB.[49] Connectors[edit] The three sizes of USB
USB
connectors are the default or standard format intended for desktop or portable equipment, the mini intended for mobile equipment , and the thinner micro size, for low-profile mobile equipment such as mobile phones and tablets. There are five speeds for USB
USB
data transfer: Low Speed, Full Speed, High Speed (from version 2.0 of the specification), SuperSpeed
SuperSpeed
(from version 3.0), and SuperSpeed+ (from version 3.1). The modes have differing hardware and cabling requirements. USB
USB
devices have some choice of implemented modes, and USB
USB
version is not a reliable statement of implemented modes. Modes are identified by their names and icons, and the specifications suggests that plugs and receptacles be colour-coded ( SuperSpeed
SuperSpeed
is identified by blue). Unlike other data buses (such as Ethernet), USB
USB
connections are directed; a host device has "downstream" facing ports that connect to the "upstream" ports of devices. Only downstream facing ports provide power; this topology was chosen to easily prevent electrical overloads and damaged equipment. Thus, USB
USB
cables have different ends: A and B, with different physical connectors for each. Each format has a plug and receptacle defined for each of the A and B ends. USB
USB
cables have plugs, and the corresponding receptacles are on the computers or electronic devices. In common practice, the A end is usually the standard format, and the B side varies over standard, mini, and micro. The mini and micro formats also provide for USB On-The-Go
USB On-The-Go
with a hermaphroditic AB receptacle, which accepts either an A or a B plug. On-The-Go
On-The-Go
allows USB
USB
between peers without discarding the directed topology by choosing the host at connection time; it also allows one receptacle to perform double duty in space-constrained applications. Connector properties[edit]

Type-A plug and, as part of a non-standard cable, receptacle

The connectors the USB
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.[50] T[51]

USB
USB
extension cable

By design, it is difficult to insert a USB
USB
plug into its receptacle incorrectly. The USB
USB
specification requires that the cable plug and receptacle be marked so the user can recognize the proper orientation. [50] The type-C plug is reversible. USB
USB
cables and small USB
USB
devices are held in place by the gripping force from the receptacle, with no screws, clips, or thumb-turns as other connectors use. The different A and B plugs prevent accidentally connecting two power sources. However, some of this directed topology is lost with the advent of multi-purpose USB
USB
connections (such as USB On-The-Go
USB On-The-Go
in smartphones, and USB-powered Wi-Fi
Wi-Fi
routers), which require A-to-A, B-to-B, and sometimes Y/splitter cables. See the USB
USB
On-The-Go connectors section below for a more detailed summary description. There are cables with A plugs on both ends, which may be valid if the cable includes, for example, a USB
USB
host-to-host transfer device with 2 ports.[52] Durability[edit] The standard connectors were designed to be more robust than many past connectors. This is because USB
USB
is hot-pluggable, and the connectors would be used more frequently, and perhaps with less care, than previous connectors. Standard USB
USB
has a minimum rated lifetime of 1,500 cycles of insertion and removal,[53] the mini- USB
USB
receptacle increases this to 5,000 cycles,[53] and the newer Micro-USB[53] and USB-C
USB-C
receptacles are both designed for a minimum rated lifetime of 10,000 cycles of insertion and removal.[54] To accomplish this, a locking device was added and the leaf-spring was moved from the jack to the plug, so that the most-stressed part is on the cable side of the connection. This change was made so that the connector on the less expensive cable would bear the most wear.[55][53] In standard USB, the electrical contacts in a USB
USB
connector are protected by an adjacent plastic tongue, and the entire connecting assembly is usually protected by an enclosing metal shell.[53] The shell on the plug makes contact with the receptacle before any of the internal pins. The shell is typically grounded, to dissipate static electricity and to shield the wires within the connector. The micro format has the highest designed insertion lifetime. The standard and mini connectors have a design lifetime of 1,500 insertion-removal cycles,[56] the improved Mini-B connectors increased this to 5,000. The micro connectors were designed with frequent charging of portable devices in mind, so have a design life of 10,000 cycles[56] and also place the flexible contacts, which wear out sooner, on the easily replaced cable, while the more durable rigid contacts are located in the receptacles. Likewise, the springy component of the retention mechanism, parts that provide required gripping force, were also moved into plugs on the cable side.[55] Compatibility[edit] The USB
USB
standard specifies tolerances for compliant USB
USB
connectors to minimize physical incompatibilities in connectors from different vendors. The USB
USB
specification also defines limits to the size of a connecting device in the area around its plug, so that adjacent ports are not blocked. Compliant devices must either fit within the size restrictions or support a compliant extension cable that does. Connector types[edit]

Various USB
USB
connectors along a centimeter ruler for scale. From left to right:

Micro-B plug UC-E6[b] Mini-B plug type-A receptacle[c] type-A plug type-B plug

^ The VBUS supply from a low-powered hub port may drop to 4.40 V. ^ UC-E6 is a proprietary non- USB
USB
connector. ^ Inverted, so the contacts are visible.

USB
USB
connector types multiplied as the specification progressed. The original USB
USB
specification detailed standard-A and standard-B plugs and receptacles.The connectors were different so that users could not connect one computer receptacle to another. The data pins in the standard plugs are recessed compared to the power pins,so that the device can power up before establishing a data connection. Some devices operate in different modes depending on whether the data connection is made. Charging docks supply power and do not include a host device or data pins, allowing any capable USB
USB
device to charge or operate from a standard USB
USB
cable. Charging cables provide power connections, but not data. In a charge-only cable, the data wires are shorted at the device end, otherwise the device may reject the charger as unsuitable. Standard connectors[edit]

Pin configuration of the type-A and type-B USB
USB
connectors, viewed from the mating (male) end of plugs

The type-A plug has an elongated rectangular cross-section, inserts into a type-A receptacle on a downstream port on a USB
USB
host or hub, and carries both power and data. Captive cables on USB
USB
devices, such as keyboards or mice, terminate with a type-A plug. The type-B 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.[57][58] The maximum allowed cross-section of the overmold boot (which is part of the connector used for its handling) is 16 by 8 mm (0.63 by 0.31 in) for the standard-A plug type, while for the type-B it is 11.5 by 10.5 mm (0.45 by 0.41 in).[59] Mini connectors[edit]

Mini-A (left) and Mini-B (right) plugs

Mini- USB
USB
connectors were introduced together with USB
USB
2.0 in April 2000, for use with smaller devices such as digital cameras, smartphones, and tablet computers. The Mini-A connector and the Mini-AB receptacle connector have been deprecated since May 2007.[60] Mini-B connectors are still supported, but are not On-The-Go-compliant;[61] the Mini-B USB
USB
connector was standard for transferring data to and from the early smartphones and PDAs. Both Mini-A and Mini-B plugs are approximately 3 by 7 mm (0.12 by 0.28 in). Micro connectors[edit]

Micro-A plug

Micro-B plug

Micro- USB
USB
connectors, which were announced by the USB-IF on 4 January 2007,[56][62] have a similar width to Mini-USB, but approximately half the thickness, enabling their integration into thinner portable devices. The Micro-A connector is 6.85 by 1.8 mm (0.270 by 0.071 in) with a maximum overmold boot size of 11.7 by 8.5 mm (0.46 by 0.33 in), while the Micro-B connector is 6.85 by 1.8 mm (0.270 by 0.071 in) with a maximum overmold size of 10.6 by 8.5 mm (0.42 by 0.33 in).[63] The thinner Micro- USB
USB
connectors were introduced to replace the Mini connectors in devices manufactured since May 2007, including smartphones, personal digital assistants, and cameras.[64] The Micro plug design is rated for at least 10,000 connect-disconnect cycles, which is more than the Mini plug design.[56][65] The Micro connector is also designed to reduce the mechanical wear on the device; instead the easier-to-replace cable is designed to bear the mechanical wear of connection and disconnection. The Universal Serial Bus Micro- USB
USB
Cables and Connectors Specification details the mechanical characteristics of Micro-A plugs, Micro-AB receptacles (which accept both Micro-A and Micro-B plugs),Double-Sided Micro USB, and Micro-B plugs and receptacles,[65] along with a standard-A receptacle to Micro-A plug adapter. OMTP standard[edit] Micro- USB
USB
was endorsed as the standard connector for data and power on mobile devices by the cellular phone carrier group Open Mobile Terminal Platform (OMTP) in 2007.[66] Micro- USB
USB
was embraced as the "Universal Charging Solution" by the International Telecommunication Union
International Telecommunication Union
(ITU) in October 2009.[67] In Europe, micro- USB
USB
became the defined common external power supply (EPS) for use with smartphones sold in the EU,[68] 14 of the world's largest mobile phone manufacturers signed the EU's common EPS Memorandum of Understanding (MoU).[69][70] Apple, one of the original MoU signers, makes Micro- USB
USB
adapters available – as permitted in the Common EPS MoU – for its iPhones equipped with Apple's proprietary 30-pin dock connector or (later) Lightning connector.[71][72] according to the CEN, CENELEC, and ETSI. USB 3.0
USB 3.0
connectors and backward compatibility[edit]

USB 3.0
USB 3.0
Micro-B SuperSpeed
SuperSpeed
plug

See also: USB 3.0
USB 3.0
§ Connectors USB 3.0
USB 3.0
introduced Type-A SuperSpeed
SuperSpeed
plugs and receptacles as well as micro-sized Type-B SuperSpeed
SuperSpeed
plugs and receptacles. The 3.0 receptacles are backward-compatible with the corresponding pre-3.0 plugs. USB 3.0
USB 3.0
and USB
USB
1.0 Type-A plugs and receptacles are designed to interoperate. To achieve USB 3.0's SuperSpeed
SuperSpeed
(and SuperSpeed+ for USB 3.1 Gen 2), 5 extra pins are added to the unused area of the original 4 pin USB 1.0 design, making USB 3.0 Type-A plugs and receptacles backward compatible to those of USB 1.0. On the device side, a modified Micro-B plug (Micro-B SuperSpeed) is used to cater for the five additional pins required to achieve the USB 3.0 features ( USB
USB
Type-C plug can also be used). The USB 3.0
USB 3.0
Micro-B plug effectively consists of a standard USB
USB
2.0 Micro-B cable plug, with an additional 5 pins plug "stacked" to the side of it. In this way, cables with smaller 5 pin USB
USB
2.0 Micro-B plugs can be plugged into devices with 10 contact USB 3.0
USB 3.0
Micro-B receptacles and achieve backward compatibility. USB
USB
cables exist with various combinations of plugs on each end of the cable, as displayed below in the USB
USB
cables matrix.

USB 3.0
USB 3.0
B type plug

USB On-The-Go
USB On-The-Go
connectors[edit] Main article: USB
USB
On-The-Go USB On-The-Go
USB On-The-Go
(OTG) introduces the concept of a device performing both master and slave roles. All current OTG devices are required to have one, and only one, USB
USB
connector: a Micro-AB receptacle. (In the past, before the development of Micro-USB, On-The-Go
On-The-Go
devices used Mini-AB receptacles). The Micro-AB receptacle is capable of accepting both Micro-A and Micro-B plugs, attached to any of the legal cables and adapters as defined in revision 1.01 of the Micro- USB
USB
specification. To enable Type-AB receptacles to distinguish which end of a cable is plugged in, plugs have an "ID" pin in addition to the four contacts in standard-size USB
USB
connectors. This ID pin is connected to GND in Type-A plugs, and left unconnected in Type-B plugs. Typically, a pull-up resistor in the device is used to detect the presence or absence of an ID connection. The OTG device with the A-plug inserted is called the A-device and is responsible for powering the USB
USB
interface when required, and by default assumes the role of host. The OTG device with the B-plug inserted is called the B-device and by default assumes the role of peripheral. An OTG device with no plug inserted defaults to acting as a B-device. If an application on the B-device requires the role of host, then the Host Negotiation Protocol (HNP) is used to temporarily transfer the host role to the B-device. OTG devices attached either to a peripheral-only B-device or a standard/embedded host have their role fixed by the cable, since in these scenarios it is only possible to attach the cable one way.[citation needed] USB-C[edit]

The USB-C
USB-C
plug

USB
USB
cable with a USB-C
USB-C
plug and a USB-C
USB-C
port on an Apple MacBook

Main article: USB-C Developed at roughly the same time as the USB 3.1 specification, but distinct from it, the USB Type-C Specification 1.0 was finalized in August 2014[73] and defines a new small reversible-plug connector for USB
USB
devices.[74] The Type-C plug connects to both hosts and devices, replacing various Type-A and Type-B connectors and cables with a standard meant to be future-proof.[73][75] The 24-pin double-sided connector provides four power-ground pairs, two differential pairs for USB 2.0 data bus (though only one pair is implemented in a Type-C cable), four pairs for SuperSpeed
SuperSpeed
data bus (only two pairs are used in USB
USB
3.1 mode), two "sideband use" pins, VCONN +5 V power for active cables, and a configuration pin for cable orientation detection and dedicated biphase mark code (BMC) configuration data channel.[76][77] Type-A and Type-B adaptors and cables are required for older devices to plug into Type-C hosts. Adapters and cables with a Type-C receptacle are not allowed.[78] Full-featured USB 3.1 Type-C cables are electronically marked cables that contain a full set of wires and a chip with an ID function based on the configuration data channel and vendor-defined messages (VDMs) from the USB Power Delivery
USB Power Delivery
2.0 specification. USB
USB
Type-C devices also support power currents of 1.5 A and 3.0 A over the 5 V power bus in addition to baseline 900 mA; devices can either negotiate increased USB
USB
current through the configuration line or they can support the full Power Delivery specification using both BMC-coded configuration line and legacy BFSK-coded VBUS line. Alternate Mode dedicates some of the physical wires in the USB-C
USB-C
cable for direct device-to-host transmission of alternate data protocols.[citation needed] The four high-speed lanes, two sideband pins, and‍—‌for dock, detachable device and permanent cable applications only‍—‌two USB 2.0 pins and one configuration pin can be used for Alternate Mode transmission. The modes are configured using VDMs through the configuration channel. Host and device interface receptacles[edit] USB
USB
plugs fit one receptacle with notable exceptions for USB
USB
On-The-Go "AB" support and the general backward compatibility of USB 3.0 as shown.

USB
USB
connectors mating table (images not to scale)

Receptacle Plug

Yes Only non- SuperSpeed No No No No No No No No

Type-A SuperSpeed Only non- SuperSpeed Yes No No No No No No No No

No No Yes No No No No No No No

Type-B SuperSpeed No No Only non- SuperSpeed Yes No No No No No No

No No No No Deprecated No No No No No

No No No No Deprecated Deprecated No No No No

No No No No No Yes No No No No

No No No No No No Yes Yes No No

No No No No No No No Yes No No

Micro-B SuperSpeed No No No No No No No Only non- SuperSpeed Yes No

No No No No No No No No No Yes

USB
USB
cables table

Plugs, each end

Micro-B SuperSpeed

Non- standard Non- standard Non- standard Yes Yes Yes Yes Yes

Non- standard No No Deprecated Deprecated Non- standard No No

Non- standard No No Non- standard Non- standard Yes No No

Yes Deprecated Non- standard No No No No Yes

Yes Deprecated Non- standard No Non- standard No No Yes

Yes Non- standard Yes No No No No Yes

Micro-B SuperSpeed Yes No No No No No No Yes

Yes No No Yes Yes Yes Yes Yes

     Non-standard Existing for specific proprietary purposes, and in most cases not inter-operable with USB-IF compliant equipment. In addition to the above cable assemblies comprising two plugs, an "adapter" cable with a Micro-A plug and a standard-A receptacle is compliant with USB specifications.[63] Other combinations of connectors are not compliant.

There do exist A-to-A assemblies, referred to as cables (such as the Easy Transfer Cable); however, these have a pair of USB
USB
devices in the middle, making them more than just cables.      Deprecated Some older devices and cables with Mini-A connectors have been certified by USB-IF. The Mini-A connector is obsolete: no new Mini-A connectors and neither Mini-A nor Mini-AB receptacles will be certified.[60]

Note: Mini-B is not deprecated, but less and less used since the arrival of Micro-B.

Pinouts[edit] See also: USB 3.0
USB 3.0
§ Pinouts USB
USB
2.0 uses two wires for power (VBUS and GND), and two for differential serial data signals. Mini and micro connectors have their GND connections moved from pin #4 to pin #5, while their pin #4 serves as an ID pin for the On-The-Go
On-The-Go
host/client identification.[79] USB 3.0 provides two additional differential pairs (four wires, SSTx+, SSTx−, SSRx+ and SSRx−), providing full-duplex data transfers at SuperSpeed, which makes it similar to Serial ATA
Serial ATA
or single-lane PCI Express.

Standard, Mini-, and Micro- USB
USB
plugs (not to scale). White areas are empty. The receptacles are pictured with USB
USB
logo to the top, looking into the open end; note this means the pin order is mirrored from plug to socket.[63]

Micro-B SuperSpeed
SuperSpeed
plug

Power (VBUS, 5 V) Data− (D−) Data+ (D+) ID (On-The-Go) GND SuperSpeed
SuperSpeed
transmit− (SSTx−) SuperSpeed
SuperSpeed
transmit+ (SSTx+) GND SuperSpeed
SuperSpeed
receive− (SSRx−) SuperSpeed
SuperSpeed
receive+ (SSRx+)

Type-A and -B pinout

Pin Name Wire color[a] Description

1 VBUS Red or Orange +5 V

2 D− White or Gold Data−

3 D+ Green Data+

4 GND Black or Blue Ground

Mini/Micro-A and -B pinout

Pin Name Wire color[a] Description

1 VBUS Red +5 V

2 D− White Data−

3 D+ Green Data+

4 ID No wire On-The-Go
On-The-Go
ID distinguishes cable ends:

"A" plug (host): connected to GND "B" plug (device): not connected

5 GND Black Signal ground

^ a b In some sources D+ and D- are erroneously swapped.

Proprietary connectors and formats[edit] Manufacturers of personal electronic devices might not include a USB standard connector on their product for technical or marketing reasons.[80] Some manufacturers provide proprietary cables that permit their devices to physically connect to a USB
USB
standard port. Full functionality of proprietary ports and cables with USB
USB
standard ports is not assured; for example, some devices only use the USB
USB
connection for battery charging and do not implement any data transfer functions.[81] Some manufacturers now offer USB
USB
magnetic port adapters; as of 2018 all product are proprietary incompatible designs. Magnetic connectors were developed mainly for mobile phones devices having Micro B, type-C or Apple's Lightning ports. They offer ease of operation and are also intended to protect the mobile device's connector from deteriorating under the mechanical action of connecting and disconnecting.[citation needed] Colors[edit]

An orange charge-only USB
USB
port on a front panel USB 3.0
USB 3.0
switch with card reader.

A blue Standard-A USB
USB
connector on a Sagemcom F@ST 3864OP ADSL modem router without USB 3.0
USB 3.0
contacts fitted.

Usual USB
USB
color-coding

Color Location Description

Black or white Ports & plugs Type-A or type-B

Blue (Pantone 300C) Ports & plugs Type-A or type-B, SuperSpeed

Teal blue Ports & plugs Type-A or type-B, SuperSpeed+

Green Ports & plugs Type-A or type-B, Qualcomm
Qualcomm
Quick Charge[82]

Yellow, orange or red Ports only High-current or sleep-and-charge

USB
USB
ports and connectors are often color-coded to distinguish their different functions and USB
USB
versions. These colors are not part of the USB
USB
specification and can vary between manufacturers; for example, USB 3.0 specification mandates appropriate color-coding while it only recommends blue inserts for standard-A USB 3.0 connectors and plugs.[83] Cabling[edit]

A USB
USB
twisted pair, where the Data+ and Data− conductors are twisted together in a double helix. The wires are enclosed in a further layer of shielding.

The D± signals used by low, full, and high speed are carried over a twisted pair (typically, unshielded) to reduce noise and crosstalk. SuperSpeed
SuperSpeed
uses separate transmit and receive differential pairs, which additionally require shielding (typically, shielded twisted pair but twinax is also mentioned by the specification). Thus, to support SuperSpeed
SuperSpeed
data transmission, cables contain twice as many wires and are thus larger in diameter.[84] The USB 1.1 standard specifies that a standard cable can have a maximum length of 5 metres (16 ft 5 in) with devices operating at full speed (12 Mbit/s), and a maximum length of 3 metres (9 ft 10 in) with devices operating at low speed (1.5 Mbit/s).[85][86][87] USB 2.0 provides for a maximum cable length of 5 metres (16 ft 5 in) for devices running at high speed (480 Mbit/s). The primary reason for this limit is the maximum allowed round-trip delay of about 1.5 μs. If USB
USB
host commands are unanswered by the USB
USB
device within the allowed time, the host considers the command lost. When adding USB
USB
device response time, delays from the maximum number of hubs added to the delays from connecting cables, the maximum acceptable delay per cable amounts to 26 ns.[88] The USB 2.0 specification requires that cable delay be less than 5.2 ns per meter (1.6 ns/ft, 192000 km/s) - which is close to the maximum achievable transmission speed for standard copper wire). The USB 3.0 standard does not directly specify a maximum cable length, requiring only that all cables meet an electrical specification: for copper cabling with AWG 26 wires the maximum practical length is 3 meters (9.8 ft).[89] Power[edit]

USB
USB
power standards

Specification Current Voltage Power (max)

Low-power device 100 mA 5 V 0.50 W

Low-power SuperSpeed
SuperSpeed
( USB
USB
3.0) device 150 mA 5 V 0.75 W

High-power device 500 mA[a] 5 V 2.5 W

High-power SuperSpeed
SuperSpeed
( USB
USB
3.0) device 900 mA[b] 5 V 4.5 W

Battery Charging (BC) 1.2 1.5 A 5 V 7.5 W

Type-C 1.5 A 5 V 7.5 W

3 A 5 V 15 W

Power Delivery 2.0 Micro-USB 3 A 20 V 60 W

Power Delivery 2.0 Type-A/B/C[c] 5 A 20 V 100 W

^ Up to five unit loads; with non- SuperSpeed
SuperSpeed
devices, one unit load is 100 mA. ^ Up to six unit loads; with SuperSpeed
SuperSpeed
devices, one unit load is 150 mA. ^ Requires active PD 5 A cable.

USB
USB
supplies power at 5 V ± 5% to power USB
USB
downstream devices. To allows for voltage drops, the voltage at the hub port is specified in the range 7000500000000000000♠5.00+0.25 −0.60 V by USB 2.0, and 7000500000000000000♠5.00+0.25 −0.55 V[90] by USB 3.0. Devices' configuration and low-power functions must operate down to 4.40 V at the hub port by USB 2.0 and that devices' configuration, low-power, and high-power functions must operate down to 4.00 V at the device port by USB 3.0. The limit to device power draw is stated in terms of a unit load, which is 100 mA or 150 mA for SuperSpeed
SuperSpeed
devices. Low-power devices may draw at most 1 unit load, and all devices must act as low-power devices before they are configured. High-power devices draw at most 5 unit loads (500 mA) or 6 unit loads (900 mA) for SuperSpeed
SuperSpeed
devices. A high-powered device must be configured, and may only draw as much power as specified in its configuration.[91][92][93][94] I.e., the maximum power may not be available. A bus-powered hub is a high-power device providing low-power ports. It draws 1 unit load for the hub controller and 1 unit load for each of at most 4 ports. The hub may also have some non-removable functions in place of ports. A self-powered hub is a device that provides high-power ports. Optionally, the hub controller may draw power for its operation as a low-power device, but all high-power ports draw from the hub's self-power. Where devices (for example, high-speed disk drives) require more power than a high-power device can draw,[95] they function erratically, if at all, from bus power of a single port. USB
USB
provides for these devices as being self-powered. However, such devices may come with a Y-shaped cable that has two USB
USB
plugs (one for power and data, the other for only power), so as to draw power as two devices.[96] Such a cable is non-standard, with the USB
USB
compliance specification stating that "use of a 'Y' cable (a cable with two A-plugs) is prohibited on any USB
USB
peripheral", meaning that "if a USB
USB
peripheral requires more power than allowed by the USB
USB
specification to which it is designed, then it must be self-powered."[97] USB
USB
Battery Charging[edit] USB
USB
Battery Charging defines a charging port,which may be a charging downstream port (CDP), with data, or a dedicated charging port (DCP) without data. Dedicated charging ports can be found on USB
USB
power adapters to run attached devices and battery packs. Charging ports on a host with both kinds will be labelled. [98] 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 200 Ω across the D+ and D− terminals.[98][99] Per the base specification, any device attached to an SDP must initially be a low-power device, with high-power mode contingent on later USB
USB
configuration by the host. Charging ports, however, can immediately supply between 0.5 and 1.5 A of current. The charging port must not apply current limiting below 0.5 A, and must not shut down below 1.5 A or before the voltage drops to 2 V.[98] Since these currents are larger than in the original standard, the extra voltage drop in the cable reduces noise margins, causing problems with High Speed signaling. Battery Charging Specification 1.1 specifies that charging devices must dynamically limit bus power current draw during High Speed signaling;[100] 1.2 specifies that charging devices and ports must be designed to tolerate the higher ground voltage difference in High Speed signaling. Revision 1.2 of the specification was released in 2010. Several changes are made and limits are increased including allowing 1.5 A on charging downstream ports for unconfigured devices, allowing High Speed communication while having a current up to 1.5 A, and allowing a maximum current of 5 A. Also, support is removed for charging port detection via resistive mechanisms.[28] Before the Battery Charging Specification was defined, there was no standardized way for the portable device to inquire how much current was available. For example, Apple's iPod and iPhone chargers indicate the available current by voltages on the D− and D+ lines. When D+ = D− = 2.0 V, the device may pull up to 500 mA. When D+ = 2.0 V and D− = 2.8 V, the device may pull up to 1 A of current.[101] When D+ = 2.8 V and D− = 2.0 V, the device may pull up to 2 A of current.[102] Accessory charging adaptors (ACA)[edit] Portable devices having an USB On-The-Go
USB On-The-Go
port may want to charge and access USB
USB
peripheral at the same time, but having only a single port (both due to On-The-Go
On-The-Go
and space requirement) prevents this. Accessory charging adapters (ACA) are devices that provide portable charging power to an On-The-Go
On-The-Go
connection between host and peripheral. ACAs have three ports: the OTG port for the portable device, which is required to have a Micro-A plug on a captive cable; the accessory port, which is required to have a Micro-AB or type-A receptacle; and the charging port, which is required to have a Micro-B receptacle, or type-A plug or charger on a captive cable. The ID pin of the OTG port is not connected within plug as usual, but to the ACA itself, where signals outside the OTG floating and ground states are used for ACA detection and state signaling. The charging port does not pass data, but does use the D± signals for charging port detection. The accessory port acts as any other port. When appropriately signaled by the ACA, the portable device can charge from the bus power as if there were a charging port present; any OTG signals over bus power are instead passed to the portable device via the ID signal. Bus power is also provided to the accessory port from the charging port transparently.[98] Power Delivery (PD)[edit] See also: List of 60W/100W USB
USB
chargeable laptops

USB
USB
PD rev. 1.0 source profiles[103]

Profile +5 V +12 V +20 V

0 Reserved

1 2.0 A, 10 W[a] N/A N/A

2 1.5 A, 18 W

3 3.0 A, 36 W

4 3.0 A, 60 W

5 5.0 A, 60 W 5.0 A, 100 W

^ Default start-up profile

USB
USB
PD rev. 2.0/3.0 source power rules[104][105]

Source output power (W) Current, at: (A)

+5 V +9 V +15 V +20 V

0.5–15 0.1–3.0 N/A N/A N/A

15–27 3.0 (15 W) 1.67–3.0

27–45 3.0 (27 W) 1.8–3.0

45–60 3.0 (45 W) 2.25–3.0

60–100 3.0–5.0

In July 2012, the USB
USB
Promoters Group announced the finalization of the USB Power Delivery
USB Power Delivery
(PD) Specification ( USB
USB
PD rev. 1), an extension that specifies using certified PD aware USB
USB
cables with standard USB
USB
Type-A and Type-B connectors to deliver increased power (more than 7.5 W) to devices with larger power demand. Devices can request higher currents and supply voltages from compliant hosts – up to 2 A at 5 V (for a power consumption of up to 10 W), and optionally up to 3 A or 5 A at either 12 V (36 W or 60 W) or 20 V (60 W or 100 W).[106] In all cases, both host-to-device and device-to-host configurations are supported.[107] The intent is to permit uniformly charging laptops, tablets, USB-powered disks and similarly higher-power consumer electronics, as a natural extension of existing European and Chinese mobile telephone charging standards. This may also affect the way electric power used for small devices is transmitted and used in both residential and public buildings.[108][109] The standard is designed to coexist with the previous USB
USB
Battery Charging specification.[110] The Power Delivery Specification defines six fixed power profiles for the power sources. PD-aware devices implement a flexible power management scheme by interfacing with the power source through a bidirectional data channel and requesting a certain level of electrical power, variable up to 5 A and 20 V depending on supported profile. The power configuration protocol uses a 24 MHz BFSK-coded transmission channel on the VBUS line. The USB Power Delivery
USB Power Delivery
Specification revision 2.0 ( USB
USB
PD rev. 2) has been released as part of the USB 3.1 suite.[104][111] It covers the Type-C cable and connector with four power/ground pairs and a separate configuration channel, which now hosts a DC coupled low-frequency BMC-coded data channel that reduces the possibilities for RF interference.[112] Power Delivery protocols have been updated to facilitate Type-C features such as cable ID function, Alternate Mode negotiation, increased VBUS currents, and VCONN-powered accessories. As of USB Power Delivery
USB Power Delivery
Specification revision 2.0, version 1.2, the six fixed power profiles for power sources have been deprecated.[113] USB
USB
PD Power Rules replace power profiles, defining four normative voltage levels at 5 V, 9 V, 15 V, and 20 V. Instead of six fixed profiles, power supplies may support any maximum source output power from 0.5 W to 100 W. The USB Power Delivery
USB Power Delivery
Specification revision 3.0 defines a programmable power supply protocol that allows granular control over VBUS power in 20 mV steps to facilitate constant current or constant voltage charging. Revision 3.0 also adds extended configuration messages, fast role swap, and deprecates the BFSK protocol.[105][114][115] As of April 2016[update], there are silicon controllers available from several sources such as TI and Cypress.[116][117] Power supplies bundled with Type-C based laptops from Apple, Google, HP, Dell, and Razer support USB
USB
PD.[118] In addition, accessories from third party vendors including Anker,[119] Belkin,[120][121] iVoler,[122] and Innergie[123] support USB
USB
PD rev. 2 at multiple voltages. Asus
Asus
make a PD compliant adapter card, the USB 3.1 UPD Panel.[124] On 8 January 2018 USB-IF announced "Certified USB
USB
Fast Charger" which will certify chargers that use the feature "Programmable Power Supply" (PPS) of the USB Power Delivery
USB Power Delivery
3.0 specification.[125] Sleep-and-charge ports[edit]

A yellow USB
USB
port denoting sleep-and-charge.

Sleep-and-charge USB
USB
ports can be used to charge electronic devices even when the computer is switched off. Normally, when a computer is powered off the USB
USB
ports are powered down, preventing phones and other devices from charging. Sleep-and-charge USB
USB
ports remain powered even when the computer is off. On laptops, charging devices from the USB
USB
port when it is not being powered from AC drains the laptop battery faster; most laptops have a facility to stop charging if their own battery charge level gets too low.[126] This feature has also been implemented on some laptop docking stations allowing device charging even when no laptop is present.[127] Sleep-and-charge USB
USB
ports may be found colored differently than regular ports, mostly red or yellow,[citation needed] though that is not always the case. On Dell and Toshiba laptops, the port is marked with the standard USB symbol with an added lightning bolt icon on the right side. Dell calls this feature PowerShare,[128] while Toshiba calls it USB Sleep-and-Charge.[129] On Acer Inc.
Acer Inc.
and Packard Bell
Packard Bell
laptops, sleep-and-charge USB
USB
ports are marked with a non-standard symbol (the letters USB
USB
over a drawing of a battery); the feature is simply called Power-off USB.[130] On some laptops such as Dell and Apple MacBook models, it is possible to plug a device in, close the laptop (putting it into sleep mode) and have the device continue to charge.[citation needed] Mobile device charger standards[edit] In China[edit] As of 14 June 2007[update], all new mobile phones applying for a license in China
China
are required to use a USB
USB
port as a power port for battery charging.[131][132] This was the first standard to use the convention of shorting D+ and D−.[133] OMTP/GSMA Universal Charging Solution[edit] In September 2007, the Open Mobile Terminal Platform group (a forum of mobile network operators and manufacturers such as Nokia, Samsung, Motorola, Sony Ericsson, and LG) announced that its members had agreed on Micro- USB
USB
as the future common connector for mobile devices.[134][135] The GSM Association
GSM Association
(GSMA) followed suit on 17 February 2009,[136][136][137][138][139] and on 22 April 2009, this was further endorsed by the CTIA – The Wireless
Wireless
Association,[140] with the International Telecommunication Union
International Telecommunication Union
(ITU) announcing on 22 October 2009 that it had also embraced the Universal Charging Solution as its "energy-efficient one-charger-fits-all new mobile phone solution," and added: "Based on the Micro- USB
USB
interface, UCS chargers will also include a 4-star or higher efficiency rating—up to three times more energy-efficient than an unrated charger."[141] EU smartphone power supply standard[edit] Main article: Common external power supply In June 2009, many of the world's largest mobile phone manufacturers signed an EC-sponsored Memorandum of Understanding (MoU), agreeing to make most data-enabled mobile phones marketed in the European Union compatible with a common External Power Supply (common EPS). The EU's common EPS specification (EN 62684:2010) references the USB
USB
Battery Charging Specification and is similar to the GSMA/OMTP and Chinese charging solutions.[142][143] In January 2011, the International Electrotechnical Commission (IEC) released its version of the (EU's) common EPS standard as IEC 62684:2011.[144] Non-standard devices[edit]

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Some USB
USB
devices require more power than is permitted by the specifications for a single port. This is common for external hard and optical disc drives, and generally for devices with motors or lamps. Such devices can use an external power supply, which is allowed by the standard, or use a dual-input USB
USB
cable, one input of which is for power and data transfer, the other solely for power, which makes the device a non-standard USB
USB
device. Some USB
USB
ports and external hubs can, in practice, supply more power to USB
USB
devices than required by the specification but a standard-compliant device may not depend on this. In addition to limiting the total average power used by the device, the USB
USB
specification limits the inrush current (i.e., the current used to charge decoupling and filter capacitors) when the device is first connected. Otherwise, connecting a device could cause problems with the host's internal power. USB
USB
devices are also required to automatically enter ultra low-power suspend mode when the USB
USB
host is suspended. Nevertheless, many USB
USB
host interfaces do not cut off the power supply to USB
USB
devices when they are suspended.[145] Some non-standard USB
USB
devices use the 5 V power supply without participating in a proper USB
USB
network, which negotiates power draw with the host interface. These are usually called USB decorations.[citation needed] Examples include USB-powered keyboard lights, fans, mug coolers and heaters, battery chargers, miniature vacuum cleaners, and even miniature lava lamps. In most cases, these items contain no digital circuitry, and thus are not standard-compliant USB
USB
devices. This may cause problems with some computers, such as drawing too much current and damaging circuitry. Prior to the USB
USB
Battery Charging Specification, the USB
USB
specification required that devices connect in a low-power mode (100 mA maximum) and communicate their current requirements to the host, which then permits the device to switch into high-power mode. Some devices, when plugged into charging ports, draw even more power (10 watts at 2.1 amperes) than the Battery Charging Specification allows — The iPad is one such device.[146] Barnes & Noble Nook Color
Nook Color
devices also require a special charger that runs at 1.9 amperes.[147] PoweredUSB[edit] Main article: PoweredUSB PoweredUSB
PoweredUSB
is a proprietary extension that adds four additional pins supplying up to 6 A at 5 V, 12 V, or 24 V. It is commonly used in point of sale systems to power peripherals such as barcode readers, credit card terminals, and printers.

The Micro- USB
USB
interface is commonly found on chargers for mobile phones

An AC adaptor with a green USB
USB
connector supporting Qualcomm
Qualcomm
Quick Charge 2.0

Australian and New Zealand power socket with USB
USB
charger socket

Y-shaped USB 3.0 cable; with such a cable, a device can draw power from two USB
USB
ports simultaneously

A small device that provides voltage and current readouts for devices charged over USB

This USB
USB
power meter additionally provides a charge readout (in mAh) and data logging

USB-powered mini fans

USB-powered vacuum cleaner

Signaling ( USB
USB
PHY)[edit] Signaling rate (transmission rate)[edit]

Mode Abbrev Gross data rate Introduced in

Low Speed LS 1.5  Mbit/s (187.5 KB/s) USB 1.0

Full Speed FS 12  Mbit/s (1.5 MB/s) USB 1.0

High Speed Also, Hi-Speed HS 480  Mbit/s (60 MB/s) USB 2.0

SuperSpeed SS 5 Gbit/s (625 MB/s) USB 3.0

SuperSpeed+ SS+ 10 Gbit/s (1.25 GB/s) USB 3.1

SuperSpeed+ SS+ 20 Gbit/s (2.5 GB/s) USB 3.2

The theoretical maximum data rate in USB 2.0 is 480 Mbit/s (60 MB/s) per controller and is shared amongst all attached devices. Some personal computer chipset manufacturers overcome this bottleneck by providing multiple USB 2.0 controllers within the southbridge. According to routine testing performed by CNet, write operations to typical Hi-Speed hard drives can sustain rates of 25–30 MB/s, while read operations are at 30–42 MB/s;[148] this is 70% of the total available bus bandwidth. For USB 3.0, typical write speed is 70–90 MB/s, while read speed is 90–110 MB/s.[148] Mask tests, also known as eye diagram tests, are used to determine the quality of a signal in the time domain. They are defined in the referenced document as part of the electrical test description for the high-speed (HS) mode at 480 Mbit/s.[149] According to a USB-IF chairman, "at least 10 to 15 percent of the stated peak 60 MB/s (480 Mbit/s) of Hi-Speed USB
USB
goes to overhead—the communication protocol between the card and the peripheral. Overhead is a component of all connectivity standards".[150] Tables illustrating the transfer limits are shown in Chapter 5 of the USB
USB
spec. For isochronous devices like audio streams, the bandwidth is constant, and reserved exclusively for a given device. The bus bandwidth therefore only has an effect on the number of channels that can be sent at a time, not the "speed" or latency of the transmission.

Low-speed (LS) rate of 1.5  Mbit/s is defined by USB 1.0. It is very similar to full-bandwidth operation except each bit takes 8 times as long to transmit. It is intended primarily to save cost in low-bandwidth human interface devices (HID) such as keyboards, mice, and joysticks. Full-speed (FS) rate of 12  Mbit/s is the basic USB
USB
data rate defined by USB 1.0. All USB
USB
hubs can operate at this speed. High-speed (HS) rate of 480  Mbit/s was introduced in 2001. All hi-speed devices are capable of falling back to full-bandwidth operation if necessary; i.e., they are backward compatible with USB 1.1 standard.[clarification needed] Connectors are identical for USB 2.0 and USB 1.x. SuperSpeed
SuperSpeed
(SS) rate of 5.0 Gbit/s. The written USB 3.0 specification was released by Intel
Intel
and its partners in August 2008. The first USB 3.0 controller chips were sampled by NEC
NEC
in May 2009,[151] and the first products using the USB 3.0 specification arrived in January 2010.[152] USB 3.0 connectors are generally backward compatible, but include new wiring and full-duplex operation. SuperSpeed+ (SS+) rate of 10 Gbit/s is defined by USB
USB
3.1 and 20 Gbit/s, using 2 lanes, is defined by USB
USB
3.2.

Transaction latency[edit] For low-speed (1.5 Mbit/s) and full-speed (12 Mbit/s) devices the shortest time for a transaction in one direction is 1 ms.[153] High-speed (480 Mbit/s) uses transactions within each micro frame (125 µs)[154] where using 1-byte interrupt packet results in a minimal response time of 940 ns. 4-byte interrupt packet results in 984 ns.[citation needed] Electrical specification[edit] USB
USB
signals are transmitted using differential signaling on a twisted-pair data cable with 90 Ω ± 15% characteristic impedance.[155]

Low-speed (LS) and Full-speed (FS) modes use a single data pair, labelled 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. High-speed (HS) mode uses the same wire pair, but with different electrical conventions. Lower signal voltages of −10 to 10 mV for low and 360 to 440 mV for logical high level, and termination of 45 Ω to ground or 90 Ω differential to match the data cable impedance. SuperSpeed
SuperSpeed
(SS) adds two additional pairs of shielded twisted wire (and new, mostly compatible expanded connectors). These are dedicated to full-duplex SuperSpeed
SuperSpeed
operation. The half-duplex lines are still used for configuration. SuperSpeed+ (SS+) uses increased data rate (Gen 2x1 mode) and/or the additional lane in the Type-C connector (Gen 1x2 and Gen 2x2 mode).

A USB
USB
connection is always between a host or hub at the A connector end, and a device or hub's "upstream" port at the other end. Signaling state[edit] The host includes 15 kΩ pull-down resistors on each data line. When no device is connected, this pulls both data lines low into the so-called single-ended zero state (SE0 in the USB
USB
documentation), and indicates a reset or disconnected connection. Line transition state[edit] The following terminology is used to assist in the technical discussion regarding USB
USB
PHY signaling.

Signal Line transition state Description USB 1.x Low Speed (1.5 kΩ pullup on D−)

USB 1.x Full Speed (1.5 kΩ pullup on D+)

D+ D− D+ D−

J Same as idle line state This is present during a transmission line transition. Alternatively, it is waiting for a new packet. low high high low

K Inverse of J state This is present during a transmission line transition. high low low high

SE0 Single-Ended Zero Both D+ and D− is low. This may indicate an end of packet signal or a detached USB
USB
device. low low low low

SE1 Single-Ended One This is an illegal state and should never occur. This is seen as an error. high high high high

The idle line state is when the device is connected to the host with a pull-up on either D+ and D−, with transmitter output on both host and device is set to high impedance (hi-Z) (disconnected output). A USB
USB
device pulls one of the data lines high with a 1.5 kΩ resistor. This overpowers one of the pull-down resistors in the host and leaves the data lines in an idle state called J. For USB 1.x, the choice of data line indicates what signal rates the device is capable of:

full-bandwidth devices pull D+ high, low-bandwidth devices pull D− high.

The K state has opposite polarity to the J state.

Line state (covering USB 1.x and 2.x)[edit]

Line state/signal Description USB 1.x Low-Speed USB 1.x Full-Speed USB 2.x High-Speed

Detached No device detected. Both lines are pulled down by 15 kΩ pull-down resistors on the host side. SE0 >= 2 µs SE0 >= 2 µs SE0 >= 2 µs

Connect USB
USB
device pull ups on D+ or D- wakes the host from detached line state. This starts the USB
USB
enumeration process. This sets the idle state. D- is pulled up by 1.5 kΩ device side. D+ is pulled up by 1.5 kΩ device side. Special
Special
chirping sequence

Idle / J Host and device transmitter at Hi-Z. Sensing line state in case of detached state.

Same as detached or connect state. Same as detached or connect state.

Sync Start of a packet line transition pattern. Line transitions: KJKJKJKK Line transitions: KJKJKJKK 15 KJ pairs followed by 2 K’s, for a total of 32 symbols.

EOP End of packet line transition pattern. Line Transitions: SE0 + SE0 + J Line Transitions: SE0 + SE0 + J

Reset Reset USB
USB
device to a known initial state. SE0 >= 2.5 ms SE0 >= 2.5 ms

Suspend Power down the device, such that it would only consume 0.5 mA from VBUS. Exits this state only after a resume or reset signal is received. To avoid this state a SOF packet (high-speed) or a keep alive (low-speed) signal is given. J >= 3 ms J >= 3 ms

Resume (host) Host wants to wake device up. K >= 20 ms then EOP pattern K >= 20 ms then EOP pattern

Resume (device) Device wants to wake up. (Must be in idle for at least 5 ms.) Device drives K >= 1 ms Host then sends a resume signal. Device drives K >= 1 ms Host then sends a resume signal.

Keep alive (low-speed) Host wants to tell low speed device to stay awake. EOP pattern once every millisecond. Not applicable Not applicable

Transmission[edit] USB
USB
data is transmitted by toggling the data lines between the J state and the opposite K state. USB
USB
encodes data using the NRZI line coding:

0 bit is transmitted by toggling the data lines from J to K or vice versa. 1 bit is transmitted by leaving the data lines as-is.

To ensure that there are enough signal transitions for clock recovery to occur in the bitstream, a bit stuffing technique is applied to the data stream: an extra 0 bit is insert into the data stream after any occurrence of six consecutive 1 bits. (Thus ensuring that there is a 0 bit to cause a transmission state transition.) Seven consecutively received 1 bits are always an error. For USB 3.0, additional data transmission encoding is used to handle the higher data rates required. Transmission example on a USB 1.1 full-speed device[edit]

Example of a Negative Acknowledge packet transmitted by USB 1.1 full-speed device when there is no more data to read. It consists of the following fields: clock synchronization byte, type of packet, and end of packet. Data packets would have more information between the type of packet and end of packet.

Synchronization Pattern: A USB
USB
packet begins with an 8-bit synchronization sequence, 00000001₂. That is, after the initial idle state J, the data lines toggle KJKJKJKK. The final 1 bit (repeated K state) marks the end of the sync pattern and the beginning of the USB
USB
frame. For high-bandwidth USB, the packet begins with a 32-bit synchronization sequence. End of Packet (EOP): EOP is indicated by the transmitter driving 2 bit times of SE0 (D+ and D− both below max.) and 1 bit time of J state. After this, the transmitter ceases to drive the D+/D− lines and the aforementioned pull-up resistors hold it in the J (idle) state. Sometimes skew due to hubs can add as much as one bit time before the SE0 of the end of packet. This extra bit can also result in a "bit stuff violation" if the six bits before it in the CRC are 1s. This bit should be ignored by receiver. Bus Reset: A USB
USB
bus is reset using a prolonged (10 to 20 milliseconds) SE0 signal.

USB 2.0 speed negotiation[edit] USB 2.0 devices use a special protocol during reset, called chirping, to negotiate the high bandwidth mode with the host/hub. A device that is USB 2.0 High Speed capable first connects as a Full Speed device (D+ pulled high), but upon receiving a USB
USB
RESET (both D+ and D− driven LOW by host for 10 to 20 ms) it pulls the D− line high, known as chirp K. This indicates to the host that the device is high bandwidth. If the host/hub is also HS capable, it chirps (returns alternating J and K states on D− and D+ lines) letting the device know that the hub operates at high bandwidth. The device has to receive at least three sets of KJ chirps before it changes to high bandwidth terminations and begins high bandwidth signaling. Because USB 3.0
USB 3.0
uses wiring separate and additional to that used by USB 2.0 and USB 1.x, such bandwidth negotiation is not required. Clock tolerance is 480.00±0.24 Mbit/s, 12.00±0.03 Mbit/s, and 1.50±0.18 Mbit/s. Though high bandwidth devices are commonly referred to as "USB 2.0" and advertised as "up to 480 Mbit/s," not all USB 2.0 devices are high bandwidth. The USB-IF certifies devices and provides licenses to use special marketing logos for either "basic bandwidth" (low and full) or high bandwidth after passing a compliance test and paying a licensing fee. All devices are tested according to the latest specification, so recently compliant low bandwidth devices are also 2.0 devices. USB 3.0[edit] USB 3 uses tinned copper stranded AWG-28 cables with 7001900000000000000♠90±7 Ω impedance for its high-speed differential pairs and linear feedback shift register and 8b/10b encoding sent with a voltage of 1 V nominal with a 100 mV receiver threshold; the receiver uses equalization.[156] SSC clock and 300 ppm precision is used. Packet headers are protected with CRC-16, while data payload is protected with CRC-32.[157] Power up to 3.6 W may be used. One unit load in Super Speed mode is equal to 150 mA.[157] Protocol layer[edit] During USB
USB
communication, data is transmitted as packets. Initially, all packets are sent from the host via the root hub, and possibly more hubs, to devices. Some of those packets direct a device to send some packets in reply. After the sync field, all packets are made of 8-bit bytes, transmitted least-significant bit first. The first byte is a packet identifier (PID) byte. The PID is actually 4 bits; the byte consists of the 4-bit PID followed by its bitwise complement. This redundancy helps detect errors. (Note also that a PID byte contains at most four consecutive 1 bits, and thus never needs bit-stuffing, even when combined with the final 1 bit in the sync byte. However, trailing 1 bits in the PID may require bit-stuffing within the first few bits of the payload.)

USB
USB
PID bytes

Type PID value (msb-first) Transmitted byte (lsb-first) Name Description

Reserved 0000 0000 1111

Token 1000 0001 1110 SPLIT High-bandwidth (USB 2.0) split transaction

0100 0010 1101 PING Check if endpoint can accept data (USB 2.0)

Special 1100 0011 1100 PRE Low-bandwidth USB
USB
preamble

Handshake ERR Split transaction error (USB 2.0)

0010 0100 1011 ACK Data packet accepted

1010 0101 1010 NAK Data packet not accepted; please retransmit

0110 0110 1001 NYET Data not ready yet (USB 2.0)

1110 0111 1000 STALL Transfer impossible; do error recovery

Token 0001 1000 0111 OUT Address for host-to-device transfer

1001 1001 0110 IN Address for device-to-host transfer

0101 1010 0101 SOF Start of frame marker (sent each ms)

1101 1011 0100 SETUP Address for host-to-device control transfer

Data 0011 1100 0011 DATA0 Even-numbered data packet

1011 1101 0010 DATA1 Odd-numbered data packet

0111 1110 0001 DATA2 Data packet for high-bandwidth isochronous transfer (USB 2.0)

1111 1111 0000 MDATA Data packet for high-bandwidth isochronous transfer (USB 2.0)

Packets come in three basic types, each with a different format and CRC (cyclic redundancy check): Handshake packets[edit]

Field Sync PID EOP

Bits

8

Signal KJ KJ KJ KK XXXX XXXX 00J

Handshake packets consist of only a single PID byte, and are generally sent in response to data packets. Error detection is provided by transmitting four bits, which represent the packet type twice, in a single PID byte using complemented form. The three basic types are ACK, indicating that data was successfully received; NAK, indicating that the data cannot be received and should be retried; and STALL, indicating that the device has an error condition and cannot transfer data until some corrective action (such as device initialization) occurs.[158][159] USB 2.0 added two additional handshake packets: NYET and ERR. NYET indicates that a split transaction is not yet complete, while ERR handshake indicates that a split transaction failed. A second use for a NYET packet is to tell the host that the device has accepted a data packet, but cannot accept any more due to full buffers. This allows a host to switch to sending small PING tokens to inquire about the device's readiness, rather than sending an entire unwanted DATA packet just to elicit a NAK.[158][159] The only handshake packet the USB
USB
host may generate is ACK. If it is not ready to receive data, it should not instruct a device to send. Token packets[edit] Token packets consist of a PID byte followed by two payload bytes: 11 bits of address and a five-bit CRC. Tokens are only sent by the host, never a device. Below are tokens present from USB
USB
1.0:

IN and OUT tokens contain a seven-bit device number and four-bit function number (for multifunction devices) and command the device to transmit DATAx packets, or receive the following DATAx packets, respectively.

IN token expects a response from a device. The response may be a NAK or STALL response or a DATAx frame. In the latter case, the host issues an ACK handshake if appropriate. OUT token is followed immediately by a DATAx frame. The device responds with ACK, NAK, NYET, or STALL, as appropriate.

SETUP operates much like an OUT token, but is used for initial device setup. It is followed by an eight-byte DATA0 frame with a standardized format. SOF (Start of Frame) Every millisecond (12000 full-bandwidth bit times), the USB
USB
host transmits a special SOF (start of frame) token, containing an 11-bit incrementing frame number in place of a device address. This is used to synchronize isochronous and interrupt data transfers. High-bandwidth USB 2.0 devices receive seven additional SOF tokens per frame, each introducing a 125 µs "microframe" (60000 high-bandwidth bit times each).

USB 2.0 also added a PING Token and a larger three-byte SPLIT Token

PING asks a device if it is ready to receive an OUT/DATA packet pair. PING is usually sent by a host when polling a device that most recently responded with NAK or NYET. This avoids the need to send a large data packet to a device that the host suspects is unwilling to accept it.[160] The device responds with ACK, NAK, or STALL, as appropriate. SPLIT is used to perform split transactions. Rather than tie up the high-bandwidth USB
USB
bus sending data to a slower USB
USB
device, the nearest high-bandwidth capable hub receives a SPLIT token followed by one or two USB
USB
packets at high-bandwidth, performs the data transfer at full- or low-bandwidth, and provides the response at high-bandwidth when prompted by a second SPLIT token. It contains a seven-bit hub number, 12 bits of control flags, and a five-bit CRC.

OUT, IN, SETUP, and PING token packets[edit]

Field Sync PID ADDR ENDP CRC5 EOP

Bits

8 7 4 5

Signal KJ KJ KJ KK XXXX XXXX XXXX XXX XXXX XXXXX 00J

ADDR: Address of USB
USB
device (maximum of 127 devices). ENDP: Select endpoint hardware source/sink buffer on device. (E.g. PID OUT would be for sending data from host source buffer into the USB device sink buffer.)

By default, all USB
USB
devices must at least support endpoint buffer 0 (EP0). This is since EP0 is used for device control and status information during enumeration and normal operation.

SOF: Start-of-frame[edit]

Field Sync PID Frame number CRC5 EOP

Bits

8 11 5

Signal KJ KJ KJ KK XXXX XXXX XXXX XXXX XXX XXXXX SE0 SE0 J

Frame number: This is a frame number that is incremented by the host periodically to allows endpoints to identify the start of the frame (or microframe) and synchronize internal endpoint clocks to the host clock.

SSPLIT and CSPLIT: Start-split transaction and complete split transaction[edit]

S/C Mode Field

0 = SSPLIT Sync PID Hub address S/C Port number S E ET CRC5 EOP

1 = CSPLIT Sync PID Hub address S/C Port number S U ET CRC5 EOP

Bits

8 7 1 7 1 1 2 5

Signal KJ KJ KJ KK XXXX XXXX XXXX XXX X XXXX XXX X X XX XXXXX SE0 SE0 J

S/C: Start complete

0 = SSPLIT: Start split transaction 1 = CSPLIT: Complete split transaction

S: 1 = Low speed, 0 = High speed E: End of full speed payload U: U bit is reserved/unused and must be reset to zero (0 B) EP: End point type (00 = control), (01 = isochronous), (10 = bulk), and (11 = interrupt)

Data packets[edit]

Field Sync PID DATA CRC16 EOP

Bits

8 0-8192 16

Signal KJ KJ KJ KK XXXX XXXX (XXXX XXXX)*byteCount XXXX XXXX XXXX XXXX SE0 SE0 J

A data packet consists of the PID followed by 0–1,024 bytes of data payload (up to 1,024 bytes for high-speed devices, up to 64 bytes for full-speed devices, and at most eight bytes for low-speed devices),[161] and a 16-bit CRC. There are two basic forms of data packet, DATA0 and DATA1. A data packet must always be preceded by an address token, and is usually followed by a handshake token from the receiver back to the transmitter. The two packet types provide the 1-bit sequence number required by stop-and-wait ARQ. If a USB
USB
host does not receive a response (such as an ACK) for data it has transmitted, it does not know if the data was received or not; the data might have been lost in transit or it might have been received but the handshake response was lost. To solve this problem, the device keeps track of the type of DATAx packet it last accepted. If it receives another DATAx packet of the same type, it is acknowledged but ignored as a duplicate. Only a DATAx packet of the opposite type is actually received. If the data is corrupted while transmitted or received, the CRC check fails. When this happens, the receiver does not generate an ACK, which makes the sender resend the packet.[162] When a device is reset with a SETUP packet, it expects an 8-byte DATA0 packet next. USB 2.0 added DATA2 and MDATA packet types as well. They are used only by high-bandwidth devices doing high-bandwidth isochronous transfers that must transfer more than 1024 bytes per 125 µs micro frame (8,192 kb/s). PRE packet (tells hubs to temporarily switch to low speed mode)[edit] A hub is able to support low bandwidth devices mixed with other speed device via a special PID value, PRE. This is required as a USB
USB
hub functions as a very simple repeater, broadcasting the host message to all connected devices regardless if the packet was for it or not. This means in a mixed speed environment, there is a potential danger that a low speed could misinterpret a high or full speed signal from the host. To eliminate this danger, if a USB hub
USB hub
detects a mix of high speed or full speed and low speed devices, it, by default, disables communication to the low speed device unless it receives a request to switch to low speed mode. On reception of a PRE packet however, it temporarily re-enables the output port to all low speed devices, to allow the host to send a single low speed packet to low speed devices. After the low speed packet is sent, an end of packet (EOP) signal tells the hub to disable all outputs to low speed devices again. Since all PID bytes include four 0 bits, they leave the bus in the full-bandwidth K state, which is the same as the low-bandwidth J state. It is followed by a brief pause, during which hubs enable their low-bandwidth outputs, already idling in the J state. Then a low-bandwidth packet follows, beginning with a sync sequence and PID byte, and ending with a brief period of SE0. Full-bandwidth devices other than hubs can simply ignore the PRE packet and its low-bandwidth contents, until the final SE0 indicates that a new packet follows.

Full speed PRE preamble Hub setup enable output to low speed devices. Low speed packet example Hub disable output to low speed devices.

Field Sync PID (PRE)

Sync PID ADDR ENDP CRC5 EOP

Bits

8

8 7 4 5

Signal KJ KJ KJ KK XXXX XXXX

KJ KJ KJ KK XXXX XXXX XXXX XXX XXXX XXXXX 00J

Transaction[edit] OUT transaction[edit]

OUT transaction (3 packets total)

Host Host Device

Packet PID OUT DATAx ACK

Packet type Token Data Handshake

Description Tell device on ADDRx to start listening for incoming data packet on endpoint EPx. Tell USB
USB
device the data that you want to send to it. Device tells the host that it has successfully received and loaded the data payload to buffer EPx.

IN transaction[edit]

IN transaction (3 packets total)

Host Device Host

Packet PID IN DATAx ACK

Packet type Token Data Handshake

Description Tell device on ADDRx to send any data that it has on its endpoint buffer EPx. Device checks its EPx endpoint buffer and sends the requested data to host. Host lets device know that it has successfully received the payload and have loaded the payload into its EPx buffer.

SETUP transaction[edit] This is used for device enumeration and connection management and informs the device that the host would like to start a control transfer exchange.

SETUP transaction (3 packets total)

Host Host Device

Packet PID SETUP DATA0 ACK

Packet type Token Data Handshake

Description Tell device on ADDRx to start setup mode and be ready for a data packet. Send to device the 8 bytes long setup packet. Device acknowledge reception of SETUP data and updates its setup state machine.

Depending on the setup packet, an optional data packet from device to host or host to device may occur.

Setup packet[edit]

Field wLength wIndex wValue bRequest bmRequestType

Offset 8 4 2 1 0

Bytes 2 2 2 1 1

Bits 16 16 16 8 1 2 5

Name Count Index Value Request Data phase transfer direction Type Recipient

Description Numbers of bytes expected to be transferred in the data stage. This is a parameter value. Depends on bRequest. Typically used for specifying endpoint or interface. This is a parameter value. Depends on bRequest. This is the setup request command. 0 = Host to device, 1 = Device to host 0 = Standard, 1 = Class, 2 = Vendor, 3 = Reserved 0 = Device, 1 = Interface, 2 = Endpoint, 3 = Other, 4 to 31 = Reserved

Control transfer exchange[edit] The control transfer exchange consist of three distinct stages:

Setup stage: This is the setup command sent by the host to the device. Data stage (optional): The device may optionally send data in response to a setup request. Status stage: Dummy IN or OUT transaction, which is probably for indicating the end of a control transfer exchange.

This allows the host to perform bus management action like enumerating new USB
USB
devices via retrieving the new device device descriptors. Retrieval of the device descriptors would especially allow for determining the USB
USB
Class, VID, and PID, which are often used for determining the correct USB
USB
driver for the device. Also, after the device descriptor is retrieved, the host performs another control transfer exchange, but instead to set the address of the USB
USB
device to a new ADDRx. Audio streaming[edit] The USB
USB
Device Working Group has laid out specifications for audio streaming. Although USB
USB
technology wasn't designed with audio streaming in mind, specific standards have been developed and implemented for audio class uses. The DWG distinguishes two audio device modes[163] specifications: Audio 1.0 specification and Audio 2.0 specification. Three types of devices are defined:

USB
USB
headphone devices USB
USB
microphone devices USB
USB
headset devices

Three levels of synchronisation were defined: asynchronous, synchronous, and adaptive.[164] Comparisons with other connection methods[edit]

A variety of USB
USB
cables for sale in Hong Kong.

FireWire[edit] At first, USB
USB
was considered a complement to IEEE 1394
IEEE 1394
(FireWire) technology, which was designed as a high-bandwidth serial bus that efficiently interconnects peripherals such as disk drives, audio interfaces, and video equipment. In the initial design, USB
USB
operated at a far lower data rate and used less sophisticated hardware. It was suitable for small peripherals such as keyboards and pointing devices. The most significant technical differences between FireWire
FireWire
and USB include:

USB
USB
networks use a tiered-star topology, while IEEE 1394 networks use a tree topology. USB 1.0, 1.1, and 2.0 use a "speak-when-spoken-to" protocol, meaning that each peripheral communicates with the host when the host specifically requests it to communicate. USB 3.0 allows for device-initiated communications towards the host. A FireWire
FireWire
device can communicate with any other node at any time, subject to network conditions. A USB
USB
network relies on a single host at the top of the tree to control the network. All communications are between the host and one peripheral. In a FireWire
FireWire
network, any capable node can control the network. USB
USB
runs with a 5 V power line, while FireWire
FireWire
in current implementations supplies 12 V and theoretically can supply up to 30 V. Standard USB hub
USB hub
ports can provide from the typical 500 mA/2.5 W of current, only 100 mA from non-hub ports. USB 3.0 and USB On-The-Go
USB On-The-Go
supply 1.8 A/9.0 W (for dedicated battery charging, 1.5 A/7.5 W full bandwidth or 900 mA/4.5 W high bandwidth), while FireWire
FireWire
can in theory supply up to 60 watts of power, although 10 to 20 watts is more typical.

These and other differences reflect the differing design goals of the two buses: USB
USB
was designed for simplicity and low cost, while FireWire
FireWire
was designed for high performance, particularly in time-sensitive applications such as audio and video. Although similar in theoretical maximum transfer rate, FireWire 400 is faster than USB 2.0 high-bandwidth in real-use,[165] especially in high-bandwidth use such as external hard drives.[166][167][168][169] The newer FireWire 800 standard is twice as fast as FireWire 400 and faster than USB 2.0 high-bandwidth both theoretically and practically.[170] However, FireWire's speed advantages rely on low-level techniques such as direct memory access (DMA), which in turn have created opportunities for security exploits such as the DMA attack. The chipset and drivers used to implement USB
USB
and FireWire
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.[171] Ethernet[edit] The IEEE 802.3af Power over Ethernet
Power over Ethernet
(PoE) standard specifies a more elaborate power negotiation scheme than powered USB. It operates at 48 V DC and can supply more power (up to 12.95 W, PoE+ 25.5 W) over a cable up to 100 meters compared to USB 2.0, which provides 2.5 W with a maximum cable length of 5 meters. This has made PoE popular for VoIP
VoIP
telephones, security cameras, wireless access points, and other networked devices within buildings. However, USB
USB
is cheaper than PoE provided that the distance is short and power demand is low. Ethernet
Ethernet
standards require electrical isolation between the networked device (computer, phone, etc.) and the network cable up to 1500 V AC or 2250 V DC for 60 seconds.[172] USB
USB
has no such requirement as it was designed for peripherals closely associated with a host computer, and in fact it connects the peripheral and host grounds. This gives Ethernet
Ethernet
a significant safety advantage over USB
USB
with peripherals such as cable and DSL modems connected to external wiring that can assume hazardous voltages under certain fault conditions.[173] MIDI[edit] Digital musical instruments are another example where USB
USB
is competitive for low-cost devices. However, Power over Ethernet
Power over Ethernet
and the MIDI
MIDI
plug standard have an advantage in high-end devices that may have long cables. USB
USB
can cause ground loop problems between equipment, because it connects ground references on both transceivers. By contrast, the MIDI
MIDI
plug standard and Ethernet
Ethernet
have built-in isolation to 500V or more. eSATA/eSATAp[edit] The e SATA
SATA
connector is a more robust SATA
SATA
connector, intended for connection to external hard drives and SSDs. eSATA's transfer rate (up to 6 Gbit/s) is similar to that of USB 3.0 (up to 5 Gbit/s on current devices; 10 Gbit/s speeds via USB 3.1, announced on 31 July 2013). A device connected by eSATA appears as an ordinary SATA
SATA
device, giving both full performance and full compatibility associated with internal drives. e SATA
SATA
does not supply power to external devices. This is an increasing disadvantage compared to USB. Even though USB
USB
3.0's 4.5 W is sometimes insufficient to power external hard drives, technology is advancing and external drives gradually need less power, diminishing the e SATA
SATA
advantage. eSATAp (power over eSATA; aka ESATA/USB) is a connector introduced in 2009 that supplies power to attached devices using a new, backward compatible, connector. On a notebook eSATAp usually supplies only 5 V to power a 2.5-inch HDD/SSD; on a desktop workstation it can additionally supply 12 V to power larger devices including 3.5-inch HDD/SSD and 5.25-inch optical drives. eSATAp support can be added to a desktop machine in the form of a bracket connecting the motherboard SATA, power, and USB
USB
resources. eSATA, like USB, supports hot plugging, although this might be limited by OS drivers and device firmware. Thunderbolt[edit] Thunderbolt combines PCI Express
PCI Express
and Mini DisplayPort
Mini DisplayPort
into a new serial data interface. Original Thunderbolt implementations have two channels, each with a transfer speed of 10 Gbit/s, resulting in an aggregate unidirectional bandwidth of 20 Gbit/s.[174] Thunderbolt 2
Thunderbolt 2
uses link aggregation to combine the two 10 Gbit/s channels into one bi-directional 20 Gbit/s channel. Thunderbolt 3
Thunderbolt 3
uses the USB
USB
Type-C connector.[175][176][177] Thunderbolt 3 has one 40 Gbit/s channel. Interoperability[edit] Main article: USB
USB
adapter Various protocol converters are available that convert USB
USB
data signals to and from other communications standards. Related standards[edit]

The Wireless
Wireless
USB
USB
logo.

The USB Implementers Forum is working on a wireless networking standard based on the USB
USB
protocol.[when?] Wireless
Wireless
USB
USB
is a cable-replacement technology, and uses ultra-wideband wireless technology for data rates of up to 480 Mbit/s. InterChip USB is a chip-to-chip variant that eliminates the conventional transceivers found in normal USB. The HSIC physical layer uses about 50% less power and 75% less board area compared to USB 2.0.[178] See also[edit]

Computing portal Electronics portal

DockPort Easy Transfer Cable Extensible Host Controller Interface (XHCI) LIO Target List of device bit rates#Peripheral Media Transfer Protocol Mobile High-Definition Link

References[edit]

^ "82371FB (PIIX) and 82371SB (PIIX3) PCI ISA IDE Xcelerator" (PDF). Intel. May 1996. Archived (PDF) from the original on 13 March 2016. Retrieved 12 March 2016.  ^ a b " USB
USB
'A' Plug Form Factor Revision 1.0" (PDF). USB
USB
Implementers Forum. 23 March 2005. p. 1. Archived (PDF) from the original on 19 May 2017. Retrieved 4 June 2017. Body length is fully 12 mm in width by 4.5 mm in height with no deviations  ^ " USB
USB
deserves more support", Business, Boston Globe Online, Simson, 31 December 1995, archived from the original on 6 April 2012, retrieved 12 December 2011  ^ a b c d e Jan Axelson, USB
USB
Complete: The Developer's Guide, Fifth Edition, Lakeview Research LLC, 2015 ,ISBN 1931448280, pages 1-7 ^ https://www.pcmag.com/encyclopedia/term/44434/how-to-install-a-pc-peripheral How to install a PC peripheral, retrieved 2018 Feb 17 ^ Icon design recommendation for Identifying USB
USB
2.0 Ports on PCs, Hosts and Hubs (PDF), USB . ^ Janssen, Cory. "What is a Universal Serial Bus (USB)?". Techopedia. Archived from the original on 3 January 2014. Retrieved 12 February 2014.  ^ Ajay Bhatt: Fellow (biography), Intel, archived from the original on 4 November 2009  ^ Rogoway, Mark (9 May 2009). " Intel
Intel
ad campaign remakes researchers into rock stars". The Oregonian. Archived from the original on 26 August 2009. Retrieved 23 September 2009.  ^ a b Pan, Hui; Polishuk, Paul (eds.). 1394 Monthly Newsletter. Information Gatekeepers. pp. 7–9. GGKEY:H5S2XNXNH99. Archived from the original on 12 November 2012. Retrieved 23 October 2012.  ^ Seebach, Peter (26 April 2005). "Standards and specs: The ins and outs of USB". IBM. Archived from the original on 2010-01-10. Retrieved 2012-09-08.  ^ a b "Eight ways the iMac changed computing". Macworld. 15 August 2008. Archived from the original on 22 December 2011. Retrieved 5 September 2017.  ^ a b " Compaq
Compaq
hopes to follow the iMac". Archived from the original on 22 October 2006.  ^ a b "The PC Follows iMac's Lead". Business week. 1999. Archived from the original on 23 September 2015.  ^ a b Popular Mechanics: Making Connections. Hearst Magazines. February 2001. p. 59. ISSN 0032-4558. Archived from the original on 15 February 2017.  ^ Universal Serial Bus 3.0 Specification (Zip). 6 June 2011. pp. 3–1. Archived from the original on 19 May 2014.  ^ Universal Serial Bus 3.0 Specification (Zip). 6 June 2011. pp. 1–3. Archived from the original on 19 May 2014.  ^ a b " USB 3.0
USB 3.0
SuperSpeed
SuperSpeed
gone wild at CES 2010, trumps even your new SSD". 9 January 2010. Archived from the original on 28 June 2011. Retrieved 20 February 2011.  ^ " USB 3.0
USB 3.0
Finally Arrives". 11 January 2010. Archived from the original on 23 February 2011. Retrieved 20 February 2011.  ^ " SuperSpeed
SuperSpeed
USB
USB
3.0: More Details Emerge". PC world. 6 January 2009. Archived from the original on 24 January 2009.  ^ "IEC and USB-IF Expand Cooperation to Support Next-Generation High-Speed Data Delivery and Device Charging Applications" (PDF) (Press release). GENEVA, Switzerland and BEAVERTON, Ore., U.S. 8 December 2014. Archived (PDF) from the original on 29 December 2014.  ^ "What's the Difference Between USB
USB
1.0 and USB
USB
2.0? - Quality Logo Products, Inc". Archived from the original on 29 December 2016. Retrieved 30 December 2016.  ^ a b "Archived copy" (PDF). Archived (PDF) from the original on 12 March 2016. Retrieved 10 March 2016.  ^ " USB
USB
3.2 will make your cables twice as fast". arstechnica.com. Archived from the original on 27 July 2017. Retrieved 27 July 2017.  ^ "4.2.1". Universal Serial Bus Specification (PDF) (Technical report). 1996. p. 29. v1.0. Archived (PDF) from the original on 30 January 2018.  ^ "5.5.4". Universal Serial Bus Specification (PDF) (Technical report). 2000. p. 40. v2.0. Archived (PDF) from the original on 2 November 2013.  ^ " USB
USB
Implementers Forum". Archived from the original on 25 July 2008.  ^ a b "Battery Charging v1.2 Spec and Adopters Agreement" (Zip). USB Implementers Forum. 7 December 2010. Archived from the original on 6 October 2014. Retrieved 5 October 2014.  ^ "USB" (PDF) (Press release). Implementers Forum. 17 November 2008. Archived from the original (PDF) on 31 March 2010. Retrieved 22 June 2010.  ^ " USB 3.0
USB 3.0
Technology" (PDF). HP. 2012. Archived from the original on 19 February 2015. Retrieved 2 January 2014.  ^ "Universal Serial Bus 3.0 Specification" (PDF). USB
USB
Implementers Forum. 2008-11-12. Retrieved 2012-12-29.  ^ a b " USB
USB
3.1 Specification Language Usage Guidelines from USB-IF" (PDF). Retrieved 2016-03-10.  ^ https://www.msi.com/blog/usb-3-1-gen1-gen2-explained ^ " USB
USB
3.1 Specification". usb.org. USB
USB
Implementers Forum, Inc. Retrieved 19 November 2014.  ^ "Universal Serial Bus Revision 3.1 Specification". usb.org. Archived from the original (ZIP) on 21 November 2014. Retrieved 19 November 2014.  ^ Saunders, Brad; Nardozza, Liz (25 July 2017). " USB 3.0
USB 3.0
Promoter Group Announces USB
USB
3.2 Update" (PDF). USB.org. USB 3.0
USB 3.0
Promoter Group. Retrieved 27 July 2017.  ^ Universal Serial Bus Specification Revision 2.0. 11 October 2011. pp. 13; 30; 256. Archived from the original (Zip) on 28 May 2012. Retrieved 8 September 2012.  ^ Universal Serial Bus Specification Revision 3.0: 8.8. 9 September 2011. pp. 8–25. Archived from the original (Zip) on 2011-11-04. Retrieved 2011-10-14. 08-Sep-2012 ^ Dan Froelich (20 May 2009). "Isochronous Protocol" (PDF). usb.org. Archived from the original (PDF) on 17 August 2014. Retrieved 21 November 2014.  ^ "Class Codes". USB
USB
Implementers Forum. Archived from the original on 2 April 2007. . ^ Use class information in the interface descriptors. This base class is defined to use in device descriptors to indicate that class information should be determined from the Interface Descriptors in the device. ^ "Universal Serial Bus Test and Measurement Class Specification (USBTMC) Revision 1.0". USB
USB
Implementers Forum. 14 April 2003.  ^ a b "Universal Serial Bus Device Class Specification for Device Firmware
Firmware
Upgrade, Version 1.1" (PDF). USB
USB
Implementers Forum. 5 August 2004. pp. 8–9. Archived (PDF) from the original on 11 October 2014. Retrieved 8 September 2014.  ^ "100 Portable Apps for your USB
USB
Stick (both for Mac and Win)". Archived from the original on 2 December 2008. Retrieved 30 October 2008.  ^ "Skype VoIP
VoIP
USB
USB
Installation Guide". Archived from the original on 6 July 2014. Retrieved 30 October 2008.  ^ "PS/2 to USB
USB
Keyboard and Mouse Adapter". Archived from the original on 12 November 2014.  ^ "Universal Serial Bus Device Class Specification for Device Firmware Upgrade, Version 1.0" (PDF). USB
USB
Implementers Forum. 1999-05-13. pp. 7–8. Archived from the original (PDF) on 2014-08-24. Retrieved 2014-09-08.  ^ "dfu-util: USB
USB
Device Firmware
Firmware
Upgrade tool". fedoraproject.org. Retrieved 2014-09-08.  ^ Karsten Nohl; Sascha Krißler; Jakob Lell (7 August 2014). "BadUSB – On accessories that turn evil" (PDF). srlabs.de. Archived from the original (PDF) on 8 August 2014. Retrieved 8 September 2014.  ^ a b Hewlett-Packard, Intel, Microsoft, NEC, ST-Ericsson, Texas Instruments (6 June 2011). Universal Serial Bus 3.0 Specification: Revision 1.0. p. 531. Archived from the original on 30 December 2013. Retrieved 26 July 2011. CS1 maint: Uses authors parameter (link) ^ " USB
USB
2.0 Specification Engineering Change-USB.org" (PDF). USB
USB
Flash Drive Alliance. Archived (PDF) from the original on 12 April 2015. Retrieved 29 December 2014.  ^ " USB
USB
connector guide". C2G. Archived from the original on 21 April 2014. Retrieved 2 December 2013.  ^ a b c d e "Universal Serial Bus Cables and Connectors Class Document Revision 2.0" (PDF). usb.org. August 2007. Archived from the original (PDF) on 11 June 2014. Retrieved 3 December 2013.  ^ Howse, Brett. " USB
USB
Type-C Connector Specifications Finalized". AnandTech. Anadtech. Archived from the original on 18 March 2017. Retrieved 24 April 2017.  ^ a b "Why was Mini- USB
USB
deprecated in favor of Micro-USB?". Stack exchange. 2011. Archived from the original on 7 December 2013. Retrieved 3 December 2013. [unreliable source?] ^ a b c d Universal Serial Bus Cables and Connectors Class Document (PDF), Revision 2.0, USB
USB
Implementers Forum, August 2007, p. 6, archived (PDF) from the original on 27 April 2015, retrieved 17 August 2014  ^ Quinnell, Richard A (24 October 1996). "USB: a neat package with a few loose ends". EDN Magazine. Reed. Archived from the original on 23 May 2013. Retrieved 18 February 2013.  ^ "What is the Difference between USB
USB
Type A and USB
USB
Type B Plug/Connector?". Archived from the original on 7 February 2017.  ^ " USB
USB
2.0 Specification Engineering Change Notice (ECN) #1: Mini-B connector" (PDF). USB-IF Developers Area. 20 October 2000. Archived (PDF) from the original on 12 April 2015. Retrieved 11 December 2014.  ^ a b " Deprecation of the Mini-A and Mini-AB Connectors" (PDF) (Press release). USB
USB
Implementers Forum. 27 May 2007. Archived (PDF) from the original on 6 March 2009. Retrieved 13 January 2009.  ^ "ID Pin Resistance on Mini B-plugs and Micro B-plugs Increased to 1 Mohm". USB
USB
IF Compliance Updates. December 2009. Archived from the original on 20 July 2011. Retrieved 1 March 2010.  ^ "Mobile phones to adopt new, smaller USB
USB
connector" (PDF) (Press release). USB
USB
Implementers Forum. 4 January 2007. Archived (PDF) from the original on 8 January 2007. Retrieved 8 January 2007.  ^ a b c "Universal Serial Bus Micro- USB
USB
Cables and Connectors Specification" (PDF). USB
USB
Implementers Forum. 2007-04-04. Archived from the original (PDF) on 2015-01-31. Retrieved 2015-01-31.  ^ "Micro- USB
USB
pinout and list of compatible smartphones and other devices". pinoutsguide.com. Archived from the original on 10 October 2013.  ^ a b "Universal Serial Bus Micro- USB
USB
Cables and Connectors Specification to the USB
USB
2.0 Specification, Revision 1.01". USB Implementers Forum. 7 April 2007. Archived from the original (Zip) on 7 February 2012. Retrieved 18 November 2010. Section 1.3: Additional requirements for a more rugged connector that is durable past 10,000 cycles and still meets the USB
USB
2.0 specification for mechanical and electrical performance was also a consideration. The Mini- USB
USB
could not be modified and remain backward compatible to the existing connector as defined in the USB
USB
OTG specification.  ^ "OMTP Local Connectivity: Data Connectivity". Open Mobile Terminal Platform. 17 September 2007. Archived from the original on 15 October 2008. Retrieved 2009-02-11.  ^ "Universal phone charger standard approved—One-size-fits-all solution will dramatically cut waste and GHG emissions". ITU (press release). Pressinfo. 22 October 2009. Archived from the original on 5 November 2009. Retrieved 4 November 2009.  ^ "Commission welcomes new EU standards for common mobile phone charger". Press Releases. Europa. 29 December 2010. Archived from the original on 19 March 2011. Retrieved 22 May 2011.  ^ New EU standards for common mobile phone charger (press release), Europa, archived from the original on 3 January 2011  ^ The following 10 biggest mobile phone companies have signed the MoU: Apple, LG, Motorola, NEC, Nokia, Qualcomm, Research In Motion, Samsung, Sony Ericsson, Texas Instruments (press release), Europa [permanent dead link] ^ "Nice Micro- USB adapter
USB adapter
Apple, now sell it everywhere", Giga om, 5 October 2011, archived from the original on 26 August 2012  ^ "Apple's Lightning to Micro- USB adapter
USB adapter
now available in US, not just Europe anymore", Engadget, 3 November 2012, archived from the original on 26 June 2017  ^ a b Howse, Brett (12 August 2014). " USB
USB
Type-C Connector Specifications Finalized". Archived from the original on 28 December 2014. Retrieved 28 December 2014.  ^ Hruska, Joel (13 March 2015). " USB-C
USB-C
vs. USB
USB
3.1: What's the difference?". ExtremeTech. Archived from the original on 11 April 2015. Retrieved 9 April 2015.  ^ Ngo, Dong (22 August 2014). " USB
USB
Type-C: One Cable to Connect Them All". cnet.com. CNET. Archived from the original on 2015-03-07. Retrieved 28 December 2014.  ^ "Technical Introduction of the New USB
USB
Type-C Connector". Archived from the original on 29 December 2014. Retrieved 29 December 2014.  ^ Smith, Ryan (22 September 2014). "DisplayPort Alternate Mode for USB Type-C Announced - Video, Power, & Data All Over Type-C". AnandTech. Archived from the original on 18 December 2014. Retrieved 28 December 2014.  ^ Universal Serial Bus Type-C Cable and Connector Specification Revision 1.1 (April 3, 2015), section 2.2, page 20 ^ " USB
USB
Pinout". usbpinout.net. Archived from the original on 17 June 2014. Retrieved 23 June 2014.  ^ "Proprietary Cables vs Standard USB". anythingbutipod.com. 30 April 2008. Archived from the original on 13 November 2013. Retrieved 29 October 2013.  ^ Lex Friedman (25 February 2013). "Review: Logitech's Ultrathin mini keyboard cover makes the wrong tradeoffs". macworld.com. Archived from the original on 3 November 2013. Retrieved 29 October 2013.  ^ Qualcomm
Qualcomm
Certified Nekteck Quick Charge
Quick Charge
2.0 54W 4 Ports USB
USB
Rapid Turbo Car Charger https://www.amazon.com/Qualcomm-Certified-Nekteck-Charger-included/dp/B016HQ24IQ/ref=cm_cr_arp_d_product_top?ie=UTF8 Retrieved 19 July 2017 ^ "Universal Serial Bus Revision 3.0 Specification, Sections 3.1.1.1 and 5.3.1.3" (ZIP). usb.org. Archived from the original on 19 May 2014. Retrieved 19 May 2014.  ^ "What is the USB 3.0
USB 3.0
Cable Difference". Hantat. 18 May 2009. Archived from the original on 11 December 2011. Retrieved 12 December 2011.  ^ " USB
USB
Cable Length Limitations" (PDF). cablesplususa.com. 3 November 2010. Archived from the original (PDF) on 11 October 2014. Retrieved 2 February 2014.  ^ "What is the Maximum Length of a USB
USB
Cable?". Techwalla.com. Archived from the original on 1 December 2017. Retrieved 18 November 2017.  ^ "Cables and Long-Haul Solutions". USB
USB
FAQ. USB.org. Archived from the original on 15 January 2014. Retrieved 2 February 2014.  ^ " USB
USB
Frequently Asked Questions". USB
USB
Implementers Forum. Archived from the original on 18 January 2011. Retrieved 10 December 2010.  ^ Axelson, Jan. " USB 3.0
USB 3.0
Developers FAQ". Archived from the original on 20 December 2016. Retrieved 20 October 2016.  ^ "7.3.2 Bus Timing/Electrical Characteristics". Universal Serial Bus Specification. USB.org. Archived from the original on 1 June 2012.  ^ "USB.org". USB.org. Archived from the original on 1 June 2012. Retrieved 22 June 2010.  ^ "Universal Serial Bus 1.1 Specification" (PDF). cs.ucr.edu. 23 September 1998. pp. 150, 158. Archived (PDF) from the original on 2 January 2015. Retrieved 24 November 2014.  ^ "Universal Serial Bus 2.0 Specification, Section 7.2.1.3 Low-power Bus-powered Functions" (ZIP). usb.org. 27 April 2000. Archived from the original on 10 September 2013. Retrieved 11 January 2014.  ^ "Universal Serial Bus 2.0 Specification, Section 7.2.1.4 High-power Bus-powered Functions" (ZIP). usb.org. 27 April 2000. Archived from the original on 10 September 2013. Retrieved 11 January 2014.  ^ "Roundup: 2.5-inch Hard Disk Drives with 500 GB, 640 GB and 750 GB Storage Capacities (page 17)". xbitlabs.com. 16 June 2010. Archived from the original on 28 June 2010. Retrieved 9 July 2010.  ^ "I have the drive plugged in but I cannot find the drive in "My Computer", why?". hitachigst.com. Archived from the original on 15 February 2011. Retrieved 30 March 2012.  ^ "USB-IF Compliance Updates". Compliance.usb.org. 1 September 2011. Archived from the original on 3 February 2014. Retrieved 22 January 2014.  ^ a b c d "Battery Charging Specification, Revision 1.2". USB Implementers Forum. 7 December 2010. Archived from the original on 28 March 2016. Retrieved 29 March 2016.  ^ Section 1.4.5, pg. 2; and Table 5-3 "Resistances", pg. 45 ^ "Battery Charging Specification, Revision 1.1". USB
USB
Implementers Forum. 15 April 2009. Archived from the original on 29 March 2014. Retrieved 2009-09-23.  ^ "The mysteries of Apple device charging", Minty Boost, Lady Ada, 2011, archived from the original on 5 August 2014  ^ Modify a cheap USB
USB
charger to feed an iPod, iPhone, 2013, archived from the original on 7 October 2011  ^ "PD_1.0" (PDF). Archived (PDF) from the original on 4 April 2016. Retrieved 27 April 2016.  ^ a b "10 Power Rules", Universal Serial Bus Power Delivery Specification revision 2.0, version 1.2, USB
USB
Implementers Forum, 25 March 2016, archived from the original on 1 June 2012, retrieved 9 April 2016  ^ a b "10 Power Rules", Universal Serial Bus Power Delivery Specification revision 3.0, version 1.1, USB
USB
Implementers Forum, archived from the original on 1 June 2012, retrieved 5 September 2017  ^ Burgess, Rick. " USB 3.0
USB 3.0
SuperSpeed
SuperSpeed
update to eliminate need for chargers". TechSpot. Archived from the original on 31 August 2013.  ^ " USB 3.0
USB 3.0
Promoter Group Announces Availability of USB
USB
Power Delivery Specification" (PDF). 18 July 2012. Archived (PDF) from the original on 20 January 2013. Retrieved 16 January 2013.  ^ "Edison's revenge". The Economist. 19 October 2013. Archived from the original on 22 October 2013. Retrieved 23 October 2013.  ^ " USB Power Delivery
USB Power Delivery
— Introduction" (PDF). 16 July 2012. Archived (PDF) from the original on 23 January 2013. Retrieved 6 January 2013.  ^ USB Power Delivery
USB Power Delivery
Archived 9 March 2013 at the Wayback Machine. ^ "USB 3.1 Specification". Archived from the original on 1 June 2012. Retrieved 11 November 2014.  ^ " USB
USB
Future Specifications Industry Reviews" (PDF). Archived (PDF) from the original on 29 July 2014. Retrieved 10 August 2014.  ^ "A. Power Profiles", Universal Serial Bus Power Delivery Specification revision 2.0, version 1.2, USB
USB
Implementers Forum, 25 March 2016, archived from the original on 12 April 2016, retrieved 9 April 2016  ^ " USB
USB
Power Delivery" (PDF). usb.org. USB-IF. 20 October 2016. Archived from the original (PDF) on 20 December 2016.  ^ "Archived copy". Archived from the original on 30 July 2017. Retrieved 30 July 2017.  ^ "Texas Instruments" (PDF). Archived (PDF) from the original on 15 April 2016. Retrieved 1 April 2016.  ^ "Cypess". Archived from the original on 30 March 2016. Retrieved 1 April 2016.  ^ " USB-C
USB-C
charging: Universal or bust! We plug in every device we have to chase the dream". Archived from the original on 5 January 2017. Retrieved 30 December 2016.  ^ "Charge All Your Devices Using the Anker PowerPort+ 5 USB-C
USB-C
with USB Power Delivery". Archived from the original on 10 November 2016. Retrieved 30 December 2016.  ^ Belkin. "Belkin® Launches USB-C
USB-C
Car Charger + Cable With Power Delivery". Archived from the original on 10 January 2017. Retrieved 30 December 2016.  ^ " Belkin
Belkin
USB-C
USB-C
Car Charger + Cable- The World's First Car Charger with Power Delivery Goes the Distance". Archived from the original on 10 November 2016. Retrieved 30 December 2016.  ^ "Get up to 60 Watts of USB Power Delivery
USB Power Delivery
Charging with the iVoler 75 W USB
USB
Type C Charger". Archived from the original on 10 November 2016. Retrieved 30 December 2016.  ^ "Innergie PowerGear USB-C
USB-C
45 charger supports multiple voltages". SlashGear. Archived from the original on 29 January 2017. Retrieved 30 December 2016.  ^ "ASUS UPD 3.1". Archived from the original on 19 June 2016.  ^ "Archived copy". Archived from the original on 9 January 2018. Retrieved 10 January 2018.  ^ "Toshiba NB200 User Manual" (PDF). UK. 1 March 2009. Archived (PDF) from the original on 19 February 2014. Retrieved 26 January 2014.  ^ "ThinkPad Ultra Dock". lenovo.com. Archived from the original on 17 September 2016. Retrieved 16 September 2016.  ^ " USB
USB
PowerShare Feature". dell.com. 5 June 2013. Archived from the original on 8 November 2013. Retrieved 4 December 2013.  ^ " USB
USB
Sleep-and-Charge Ports". toshiba.com. Archived from the original on 14 December 2014. Retrieved 21 December 2014.  ^ " USB
USB
Charge Manager". packardbell.com. Retrieved 2014-04-25.  ^ Cai Yan (31 May 2007). " China
China
to enforce universal cell phone charger". EE Times. Archived from the original on 29 September 2007. Retrieved 25 August 2007.  ^ The Chinese FCC's technical standard: "YD/T 1591-2006, Technical Requirements and Test Method of Charger and Interface for Mobile Telecommunication Terminal Equipment" (PDF) (in Chinese). Dian yuan. Archived (PDF) from the original on 15 May 2011.  ^ Lam, Crystal; Liu, Harry (22 October 2007). "How to conform to China's new mobile phone interface standards". Wireless
Wireless
Net DesignLine. Archived from the original on 14 May 2014. Retrieved 22 June 2010.  ^ "Pros seem to outdo cons in new phone charger standard". News. 20 September 2007. Retrieved 2007-11-26.  ^ "Broad Manufacturer Agreement Gives Universal Phone Cable Green Light" (Press release). OTMP. 17 September 2007. Archived from the original on 29 June 2009. Retrieved 26 November 2007.  ^ a b "Agreement on Mobile phone
Mobile phone
Standard Charger" (Press release). GSM World. Archived from the original on 17 February 2009.  ^ "Common Charging and Local Data Connectivity". Open Mobile Terminal Platform. 11 February 2009. Archived from the original on 29 March 2009. Retrieved 2009-02-11.  ^ "Universal Charging Solution ~ GSM World". GSM world. Archived from the original on 26 June 2010. Retrieved 22 June 2010.  ^ "Meeting the challenge of the universal charge standard in mobile phones". Planet Analog. Retrieved 2010-06-22. [permanent dead link] ^ "The Wireless
Wireless
Association Announces One Universal Charger Solution to Celebrate Earth Day" (Press release). CTIA. 22 April 2009. Archived from the original on 14 December 2010. Retrieved 22 June 2010.  ^ "ITU" (Press release). 22 October 2009. Archived from the original on 27 March 2010. Retrieved 22 June 2010.  ^ "chargers". EU: EC. 29 June 2009. Archived from the original on 23 October 2009. Retrieved 22 June 2010.  ^ "Europe gets universal cellphone charger in 2010". Wired. 13 June 2009. Archived from the original on 18 August 2010. Retrieved 22 June 2010.  ^ "One size-fits-all mobile phone charger: IEC publishes first globally relevant standard". International Electrotechnical Commission. 1 February 2011. Archived from the original on 3 January 2012. Retrieved 20 February 2012.  ^ "Part 2 - Electrical". MQP Electronics Ltd. Archived from the original on 24 December 2014. Retrieved 29 December 2014.  ^ "Watt to Know About iPhone & iPad Power Adapters Analysis". The Mac Observer. Archived from the original on 10 December 2011. Retrieved 12 December 2011.  ^ " Nook Color
Nook Color
charger uses special Micro- USB
USB
connector". barnesandnoble.com. 3 July 2011. Archived from the original on 11 February 2012.  ^ a b "Seagate FreeAgent GoFlex Ultra-portable" (review). CNet. Archived from the original on 14 April 2011. Retrieved 22 May 2011.  ^ Schwarz, Rohde (2012-05-25). " USB
USB
2.0 Mask Testing" (PDF). Retrieved 2012-07-12. [permanent dead link] ^ " USB
USB
2.0's Real Deal", News & Trends, PC World, 28 February 2002, archived from the original on 5 December 2010  ^ " NEC
NEC
ready to sample 'world's first' USB 3.0
USB 3.0
controller chip". Archived from the original on 23 May 2009. Retrieved 15 June 2009.  ^ "When will USB 3.0 products hit the market?". Archived from the original on 30 April 2009. Retrieved 11 May 2009.  ^ "Mouse stuff you ought to know about", Urban terror, 9 August 2008, archived from the original on 11 October 2014  ^ OS dev - Universal Serial Bus, 1 February 2011, archived from the original on 5 September 2012  ^ " USB
USB
in a NutShell—Chapter 2—Hardware". Beyond Logic.org. Archived from the original on 20 August 2007. Retrieved 25 August 2007.  ^ "Technical Specifications of the USB 3.0
USB 3.0
SuperSpeed
SuperSpeed
Cables". Archived from the original on 14 April 2011.  100717 usb3.com ^ a b "Universal Serial Bus 3.0 Specification, Rev 1.0 November 12, 2008" (PDF). Archived (PDF) from the original on 13 November 2013.  100717 usb3.com ^ a b " USB
USB
Made Simple, Part 3. Data Flow". usbmadesimple.co.uk. 2008. Archived from the original on 5 October 2014. Retrieved 17 August 2014.  ^ a b " USB
USB
in a NutShell, Chapter 3. USB
USB
Protocols". beyondlogic.org. 17 September 2010. Archived from the original on 5 August 2014. Retrieved 17 August 2014.  ^ "Part 7, High Speed Transactions: Ping Protocol". usbmadesimple.co.uk. 2008. Archived from the original on 3 October 2014. Retrieved 16 August 2014.  ^ " USB
USB
in a Nut Shell". Chapter 4 - Endpoint Types. Archived from the original on 2 September 2014. Retrieved 5 September 2014.  ^ "Debugging Common USB
USB
Issues". Archived from the original on 15 June 2013. Retrieved 5 June 2013.  ^ www.usb.org/developers/docs/devclass_docs/BasicAudioDevice-10.zip ^ "32-bit Atmel Microcontroller
Microcontroller
Application Note" (PDF). Atmel Corporation. 2011. Archived (PDF) from the original on 6 May 2016. Retrieved 13 April 2016.  ^ " FireWire
FireWire
vs. USB
USB
2.0" (PDF). QImaging. Archived (PDF) from the original on 11 October 2010. Retrieved 20 July 2010.  ^ " FireWire
FireWire
vs. USB 2.0 – Bandwidth Tests". Archived from the original on 12 August 2007. Retrieved 25 August 2007.  ^ "USB 2.0 vs FireWire". Pricenfees. Archived from the original on 16 October 2016. Retrieved 25 August 2007.  ^ Metz, Cade (25 February 2003). "The Great Interface-Off: FireWire Vs. USB 2.0". PC Magazine. Archived from the original on 30 September 2007. Retrieved 25 August 2007.  ^ Heron, Robert. "USB 2.0 Versus FireWire". TechTV. Archived from the original on 29 September 2007. Retrieved 25 August 2007.  ^ " FireWire
FireWire
vs. USB 2.0". USB
USB
Ware. Archived from the original on 16 March 2007. Retrieved 19 March 2007.  ^ Key, Gary (15 November 2005). "Firewire and USB
USB
Performance". Archived from the original on 23 April 2008. Retrieved 1 February 2008.  ^ "802.3, Section 14.3.1.1" (PDF). IEEE. Archived (PDF) from the original on 6 December 2010.  ^ "Powerbook Explodes After Comcast Plugs In Wrong Cable". Consumerist. 8 March 2010. Archived from the original on 25 June 2010. Retrieved 22 June 2010.  ^ "How Thunderbolt Technology Works: Thunderbolt Technology Community". Thunderbolttechnology.net. Archived from the original on 10 February 2014. Retrieved 22 January 2014.  ^ One port to rule them all: Thunderbolt 3 and USB
USB
Type-C join forces, archived from the original on 2 June 2015, retrieved 2 June 2015  ^ Thunderbolt 3
Thunderbolt 3
is twice as fast and uses reversible USB-C, archived from the original on 3 June 2015, retrieved 2 June 2015  ^ Thunderbolt 3 embraces USB
USB
Type-C connector, doubles bandwidth to 40 Gbps, archived from the original on 3 June 2015, retrieved 2 June 2015  ^ "Interchip Connectivity: HSIC, UniPro, HSI, C2C, LLI... oh my!". Archived from the original on 19 June 2011. Retrieved 24 June 2011. 

Further reading[edit]

Axelson, Jan (1 September 2006). USB
USB
Mass Storage: Designing and Programming Devices and Embedded Hosts (1st ed.). Lakeview Research. ISBN 978-1-931-44804-8.  ——— (1 December 2007). Serial Port Complete: COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems (2nd ed.). Lakeview Research. ISBN 978-1-931-44806-2.  ——— (2015). USB
USB
Complete: The Developer's Guide (5th ed.). Lakeview Research. ISBN 978-1-931448-28-4.  524 pp. Hyde, John (February 2001). USB
USB
Design by Example: A Practical Guide to Building I/O Devices (2nd ed.). Intel
Intel
Press. ISBN 978-0-970-28465-5.  "Debugging USB
USB
2.0 for Compliance: It's Not Just a Digital World" (PDF). Technologies Application Note (1382–3). Agilent. Archived from the original (PDF) on 25 July 2012. 

External links[edit]

Wikimedia Commons has media related to USB.

The Wikibook Serial Programming: USB
USB
Technical Manual has a page on the topic of: USB
USB
connectors

" USB
USB
Implementers Forum".  "Universal Host Controller Interface (UHCI)" (PDF). Intel.  " USB 3.0
USB 3.0
Standard-A, Standard-B, Powered-B connectors". Pinouts guide.  "Characterization and compliance test". Agilent.  Muller, Henk. "How To Create And Program USB
USB
Devices," Electronic Design, July 2012 An Analysis of Throughput Characteristics of Universal Serial Bus, June 1996, by John Garney USB 2.0 Protocol Engine, October 2010, by Razi Hershenhoren and Omer Reznik IEC international standard: IEC 62680 Universal serial bus interfaces for data and power:

IEC 62680-1.1:2015 - Part 1-1: Common components - USB
USB
Battery Charging Specification, revision 1.2 IEC 62680-1-2:2016 - Part 1-2: Common components - USB
USB
Power Delivery specification revision 1.0 IEC 62680-1-3:2016 - Part 1-3: Universal Serial Bus interfaces - Common components -, revision 1.0 IEC 62680-2-1:2015 - Part 2-1: Universal Serial Bus Specification, Revision 2.0 IEC 62680-2-2:2015 - Part 2-2: Micro- USB
USB
Cables and Connectors Specification, Revision 1.01 IEC 62680-2-3:2015 - Part 2-3: Universal Serial Bus Cables and Connectors Class Document Revision 2.0

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List of International Electrotechnical Commission
International Electrotechnical Commission
standards

IEC standards

IEC 60027 IEC 60034 IEC 60038 IEC 60062 IEC 60063 IEC 60068 IEC 60112 IEC 60228 IEC 60269 IEC 60297 IEC 60309 IEC 60320 IEC 60364 IEC 60446 IEC 60559 IEC 60601 IEC 60870

IEC 60870-5 IEC 60870-6

IEC 60906-1 IEC 60908 IEC 60929 IEC 60958

AES3 S/PDIF

IEC 61030 IEC 61131

IEC 61131-3

IEC 61158 IEC 61162 IEC 61334 IEC 61346 IEC 61355 IEC 61400 IEC 61499 IEC 61508 IEC 61511 IEC 61850 IEC 61851 IEC 61883 IEC 61960 IEC 61968 IEC 61970 IEC 62014-4 IEC 62056 IEC 62061 IEC 62196 IEC 62262 IEC 62264 IEC 62304 IEC 62325 IEC 62351 IEC 62365 IEC 62366 IEC 62379 IEC 62386 IEC 62455 IEC 62680 IEC 62682 IEC 62700

ISO/IEC standards

ISO/IEC 646 ISO/IEC 2022 ISO/IEC 4909 ISO/IEC 5218 ISO/IEC 6429 ISO/IEC 6523 ISO/IEC 7810 ISO/IEC 7811 ISO/IEC 7812 ISO/IEC 7813 ISO/IEC 7816 ISO/IEC 7942 ISO/IEC 8613 ISO/IEC 8632 ISO/IEC 8652 ISO/IEC 8859 ISO/IEC 9126 ISO/IEC 9293 ISO/IEC 9592 ISO/IEC 9593 ISO/IEC 9899 ISO/IEC 9945 ISO/IEC 9995 ISO/IEC 10021 ISO/IEC 10116 ISO/IEC 10165 ISO/IEC 10179 ISO/IEC 10646 ISO/IEC 10967 ISO/IEC 11172 ISO/IEC 11179 ISO/IEC 11404 ISO/IEC 11544 ISO/IEC 11801 ISO/IEC 12207 ISO/IEC 13250 ISO/IEC 13346 ISO/IEC 13522-5 ISO/IEC 13568 ISO/IEC 13818 ISO/IEC 14443 ISO/IEC 14496 ISO/IEC 14882 ISO/IEC 15288 ISO/IEC 15291 ISO/IEC 15408 ISO/IEC 15444 ISO/IEC 15445 ISO/IEC 15504 ISO/IEC 15511 ISO/IEC 15693 ISO/IEC 15897 ISO/IEC 15938 ISO/IEC 16262 ISO/IEC 17024 ISO/IEC 17025 ISO/IEC 18000 ISO/IEC 18004 ISO/IEC 18014 ISO/IEC 19752 ISO/IEC 19757 ISO/IEC 19770 ISO/IEC 19788 ISO/IEC 20000 ISO/IEC 21000 ISO/IEC 21827 ISO/IEC 23000 ISO/IEC 23003 ISO/IEC 23008 ISO/IEC 23270 ISO/IEC 23360 ISO/IEC 24707 ISO/IEC 24727 ISO/IEC 24744 ISO/IEC 24752 ISO/IEC 26300 ISO/IEC 27000 ISO/IEC 27000-series ISO/IEC 27002 ISO/IEC 27040 ISO/IEC 29119 ISO/IEC 33001 ISO/IEC 38500 ISO/IEC 42010 ISO/IEC 80000

Related

International Electrotechnical Commission

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Basic computer components

Input devices

Keyboard Image scanner Microphone Pointing device

Graphics tablet Joystick Light pen Mouse

Optical

Pointing stick Touchpad Touchscreen Trackball

Webcam

Softcam

Refreshable braille display

Output devices

Monitor Refreshable braille display Printer Speakers Plotter

Removable data storage

Optical disc

CD DVD Blu-ray

Disk pack Floppy disk Memory card USB
USB
flash drive

Computer
Computer
case

Central processing unit
Central processing unit
(CPU) HDD / SSD / SSHD Motherboard Network interface controller Power supply Random-access memory
Random-access memory
(RAM) Sound card Video card Fax modem Expansion card

Ports

Ethernet FireWire
FireWire
(IEEE 1394) Parallel port Serial port PS/2 port USB Thunderbolt HDMI
HDMI
/ DVI / VGA eSATA Audio jack

v t e

Technical and de facto standards for wired computer buses

General

System bus Front-side bus Back-side bus Daisy chain Control bus Address bus Bus contention Network on a chip Plug and play List of bus bandwidths

Standards

SS-50 bus S-100 bus Multibus Unibus VAXBI MBus STD Bus SMBus Q-Bus Europe Card Bus ISA STEbus Zorro II Zorro III CAMAC FASTBUS LPC HP Precision Bus EISA VME VXI VXS NuBus TURBOchannel MCA SBus VLB PCI PXI HP GSC bus InfiniBand UPA PCI Extended (PCI-X) AGP PCI Express
PCI Express
(PCIe) Direct Media Interface (DMI) RapidIO Intel
Intel
QuickPath Interconnect NVLink HyperTransport

Infinity Fabric

Intel
Intel
UltraPath Interconnect

Storage

ST-506 ESDI IPI SMD Parallel ATA
Parallel ATA
(PATA) SSA DSSI HIPPI Serial ATA
Serial ATA
(SATA) SCSI

Parallel SAS

Fibre Channel SATAe PCI Express
PCI Express
(via AHCI or NVMe logical device interface)

Peripheral

Apple Desktop Bus DCB HP-IL HIL MIDI RS-232 RS-422 RS-423 RS-485 DMX512-A IEEE-488
IEEE-488
(GPIB) IEEE-1284 (parallel port) UNI/O ACCESS.bus 1-Wire D²B I²C SPI Parallel SCSI Profibus IEEE 1394
IEEE 1394
(FireWire) USB Camera Link External PCIe Thunderbolt

Audio

ADAT Lightpipe AES3 Intel
Intel
HD Audio I²S MADI McASP S/PDIF TOSLINK

Portable

PC Card ExpressCard

Embedded

Multidrop bus CoreConnect AMBA Wishbone SLIMbus

Interfaces are listed by their speed in the (roughly) ascending order, so the interface at the end of each section should be the fastest. Category

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DC power delivery

USB
USB
based

Common External Power Supply (for mobile phones) USB
USB
Power Delivery PoweredUSB

Not USB
USB
based

AC adapter Power supply unit (computer) Universal Power Adapter for Mobile Devices (IEEE P1823) DC Power supply for notebook co

.