HOME
The Info List - USB



--- Advertisement ---


(i)

USB, short for UNIVERSAL SERIAL BUS, is an industry standard that defines cables, connectors and communications protocols for connection, communication, and power supply between computers and devices.

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 a variety of earlier interfaces, such as serial ports and parallel ports , as well as separate power chargers for portable devices – and has become commonplace on a wide range of devices.

Created in the mid-1990s, it is currently developed by the USB Implementers Forum ( USB
USB
IF).

CONTENTS

* 1 Overview

* 2 History

* 2.1 Version history

* 2.1.1 Overview * 2.1.2 Power related specifications * 2.1.3 USB
USB
1.x * 2.1.4 USB
USB
2.0 * 2.1.5 USB 3.0 * 2.1.6 USB 3.1

* 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 Upgrade

* 5 Connectors

* 5.1 Connector properties

* 5.1.1 Receptacles and plugs * 5.1.2 Usability and orientation * 5.1.3 Power-use topology * 5.1.4 Durability * 5.1.5 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 Non-standard cables * 5.2.5 USB 3.0 connectors and backward compatibility * 5.2.6 USB On-The-Go connectors * 5.2.7 USB-C * 5.2.8 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
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 Signalling ( USB
USB
PHY)

* 8.1 Signalling rate (transmission rate)

* 8.1.1 Transaction latency

* 8.2 Electrical specification

* 8.3 Signalling state

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

* 8.4 Transmission

* 8.4.1 Transmission example on a USB
USB
1.1 Full Speed Device

* 8.5 USB
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
Ethernet
* 12.3 MIDI
MIDI
* 12.4 eSATA/eSATAp * 12.5 Thunderbolt

* 13 Interoperability * 14 Related standards * 15 See also * 16 Notes * 17 References * 18 Further reading * 19 External links

OVERVIEW

In general, there are three basic formats of USB
USB
connectors: the default or _standard_ format intended for desktop or portable equipment (for example, on USB
USB
flash drives ), the _mini_ intended for mobile equipment (now deprecated except the Mini-B, which is used on many cameras), and the thinner _micro_ size, for low-profile mobile equipment (most modern mobile phones). Also, there are 5 modes of USB data transfer, in order of increasing bandwidth: Low Speed (from 1.0), Full Speed (from 1.0), High Speed (from 2.0), SuperSpeed (from 3.0), and SuperSpeed+ (from 3.1); 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 is identified by blue).

Unlike other data buses (e.g., Ethernet, HDMI), USB
USB
connections are directed, with both upstream and downstream ports emanating from a single host. This applies to electrical power, with only downstream facing ports providing 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. Therefore, in general, each different format requires four different connectors: a plug and receptacle for each of the A and B ends. USB
USB
cables have the 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 with a hermaphroditic AB receptacle, which accepts either an A or a B plug. 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.

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, but they could also be non-standard and erroneous and should be used carefully.

The micro format is the most durable from the point of view of designed insertion lifetime. The standard and mini connectors have a design lifetime of 1,500 insertion-removal cycles, 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 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.

HISTORY

_ The basic USB
USB
trident_ logo _ USB
USB
logo on the head of a standard A plug (the most common USB
USB
plug ).

A group of seven companies began the development of USB
USB
in 1994: Compaq , DEC , IBM
IBM
, Intel
Intel
, Microsoft
Microsoft
, NEC
NEC
, and Nortel
Nortel
. 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; the first integrated circuits supporting USB
USB
were produced by Intel
Intel
in 1995.

The original USB
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_. 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 . Apple Inc. 's iMac was the first mainstream product with USB
USB
and the iMac's success popularized USB
USB
itself. 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.

The USB
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 (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 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. USB 3.0 includes a new, higher speed bus called SuperSpeed in parallel with the USB
USB
2.0 bus. For this reason, the new version is also called SuperSpeed. The first USB 3.0 equipped devices were presented in January 2010.

As of 2008 , approximately 6 billion USB
USB
ports and interfaces were in the global marketplace, and about 2 billion were being sold each year.

In December 2014, USB-IF submitted USB
USB
3.1, USB Power Delivery 2.0 and 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.

VERSION HISTORY

Overview

RELEASE NAME RELEASE DATE MAXIMUM TRANSFER RATE NOTE

USB
USB
0.8 December 1994

Prerelease

USB
USB
0.9 April 1995

Prerelease

USB
USB
0.99 August 1995

Prerelease

USB
USB
1.0 Release Candidate November 1995

Prerelease

USB
USB
1.0 January 1996 Low Speed (1.5 Mbit/s)

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

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

USB
USB
3.0 November 2008 SuperSpeed (5 Gbit/s) Also referred to as USB 3.1 Gen 1 by USB 3.1 standard

USB
USB
3.1 July 2013 SuperSpeed+ (10 Gbit/s) Also referred to as USB 3.1 Gen 2 by USB 3.1 standard

USB
USB
3.2 ?-September 2017 SuperSpeed++ (20 Gbit/s) Also referred to as USB 3.1 Gen 3 by USB 3.1 standard

Power Related Specifications

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

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

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

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

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

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

USB
USB
1.x

Released in January 1996, USB
USB
1.0 specified a data rate of 1.5 Mbit/s _(Low Bandwidth_ or _Low Speed)_. 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
USB
1.1 was released in August 1998, which introduced the speed of 12 Mbit/s _(full speed)_. USB
USB
1.1 was the earliest revision that was widely adopted and led to what Microsoft
Microsoft
designated the " Legacy-free PC ".

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 peripheral devices, 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

The Hi-Speed USB
USB
logo A USB
USB
2.0 PCI expansion card

USB
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
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.

Further 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:

* _Mini-A and Mini-B Connector ECN_: Released in October 2000. Specifications for Mini-A and Mini-B plug and receptacle. Also receptacle that accepts both plugs for On-The-Go. These should not be confused with Micro-B plug and receptacle. * _Pull-up/Pull-down Resistors ECN_: Released in May 2002

* _Interface Associations ECN_: Released in May 2003. New standard descriptor was added that allows associating multiple interfaces with a single device function. * _Rounded Chamfer ECN_: Released in October 2003. A recommended, backward compatible change to Mini-B plugs that results in longer lasting connectors. * _ Unicode
Unicode
ECN_: Released in February 2005. This ECN specifies that strings are encoded using UTF-16LE . USB
USB
2.0 specified Unicode
Unicode
, but did not specify the encoding. * _Inter-Chip USB
USB
Supplement_: Released in March 2006

* _On-The-Go Supplement 1.3_: Released in December 2006. USB On-The-Go makes it possible for two USB
USB
devices to communicate with each other without requiring a separate USB
USB
host. In practice, one of the USB
USB
devices acts as a host for the other device. * _Battery Charging Specification 1.1_: Released in March 2007 and updated on 15 April 2009. Adds support for dedicated chargers (power supplies with USB connectors), host chargers ( USB
USB
hosts that can act as chargers) and the No Dead Battery provision, which allows devices to temporarily draw 100 mA current after they have been attached. If a USB
USB
device is connected to a dedicated charger, maximum current drawn by the device may be as high as 1.8 A. (Note that this document is not distributed with USB
USB
2.0 specification package, only USB 3.0 and USB
USB
On-The-Go.) * _Micro- USB
USB
Cables and Connectors Specification 1.01_: Released in April 2007.

* _Link Power Management Addendum ECN_: Released in July 2007. This adds _sleep_, a new power state between enabled and suspended states. Device in this state is not required to reduce its power consumption. However, switching between enabled and sleep states is much faster than switching between enabled and suspended states, which allows devices to sleep while idle. * _Battery Charging Specification 1.2_: Released in December 2010. Several changes and increasing limits including allowing 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.

USB
USB
3.0

Main article: USB 3.0 The 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 USB
USB
Developers Conference.

USB 3.0 defines a new _SuperSpeed_ transfer mode, with associated new backward compatible plugs, receptacles, and cables. SuperSpeed plugs and receptacles are identified with a distinct logo and blue inserts in standard format receptacles.

The new 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 only around 3.2 Gbit/s (0.4 GB/s or 400 MB/s). However, this should increase with future hardware advances. Communication is full-duplex in SuperSpeed transfer mode; earlier modes are half-duplex, arbitrated by the host.

Low-power and high-power devices remain operational with this standard, but devices using SuperSpeed can take advantage of increased available current of between 150 mA and 900 mA, respectively. Additionally, there is a Battery Charging Specification (Version 1.2 – December 2010), which increases the power handling capability to 1.5 A but does _not_ allow concurrent data transmission. The Battery Charging Specification requires that the physical ports themselves be capable of handling 5 A of current but limits the maximum current drawn to 1.5 A.

USB
USB
3.1

Main article: USB 3.1

A January 2013 press release, from the USB
USB
group revealed plans to update USB 3.0 to 10 Gbit/s. The group ended up creating a new USB specification, USB
USB
3.1, which was released on 31 July 2013, replacing the USB 3.0 standard. The USB 3.1 specification takes over the existing USB
USB
3.0's _ SuperSpeed USB_ transfer rate, also referred to as _ USB 3.1 Gen 1_, and introduces a faster transfer rate called _ SuperSpeed USB
USB
10 Gbps_, also referred to as _ USB 3.1 Gen 2,_ putting it on par with a single first-generation Thunderbolt channel. The new mode's logo features a caption stylized as _SUPERSPEED+_. The USB 3.1 Gen 2 standard increases the data signaling rate to 10 Gbit/s, double that of SuperSpeed USB, and reduces line encoding overhead to just 3% by changing the encoding scheme to 128b/132b . The first USB 3.1 Gen 2 implementation demonstrated transfer speeds of 7.2 Gbit/s.

The USB 3.1 standard is backward compatible with USB 3.0 and USB
USB
2.0.

SYSTEM DESIGN

The design architecture of USB
USB
is asymmetrical in its topology, consisting of a host , a multitude of downstream USB
USB
ports, and multiple peripheral devices connected in a tiered-star topology . Additional USB
USB
hubs may be included in the tiers, allowing branching into a tree structure with up to five tier levels. A USB
USB
host may implement multiple host controllers and each host controller may provide one or more USB
USB
ports. Up to 127 devices, including hub devices if present, may be connected to a single host controller. USB
USB
devices are linked in series through hubs. One hub—built into the host controller—is the root hub.

A physical USB
USB
device may consist of several logical sub-devices that are referred to as _device functions_. A single device may provide several functions, for example, a webcam (video device function) with a built-in microphone (audio device function). This kind of device is called a _composite device_. 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 actually 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 1-to-1 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_, _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 transfers Devices that need guaranteed quick responses (bounded latency) (e.g., pointing devices and keyboards) Bulk transfers Large sporadic transfers using all remaining available bandwidth, but with no guarantees on bandwidth or latency (e.g., file transfers)

An endpoint of a pipe is addressable with a tuple _(device_address, endpoint_number)_ as specified in a TOKEN packet that the host sends when it wants to start a data transfer session. If the direction of the data transfer is from the host to the endpoint, an OUT packet (a specialization of a TOKEN packet) having the desired device address and endpoint number is sent by the host. If the direction of 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
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
USB
2.0, the host controller polls the bus for traffic, usually in a round-robin fashion. The throughput of each 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
USB
2.0 hubs contain devices called transaction translators that convert between high-speed USB
USB
2.0 buses and full and low speed buses. When a high-speed USB
USB
2.0 hub is plugged into a high-speed USB
USB
host or hub, it operates in high-speed mode. The USB hub then uses either one transaction translator per hub to create a full/low-speed bus routed to all full and low speed devices on the hub, or uses one transaction translator per port to create an isolated full/low-speed bus per port on the hub.

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
USB
2.0 or earlier devices connected to that host. Operating data rates for earlier devices are set in the legacy manner.

DEVICE CLASSES

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:

CLASS USAGE DESCRIPTION EXAMPLES, OR EXCEPTION

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

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

02h Both Communications and CDC Control Modem
Modem
, Ethernet
Ethernet
adapter , Wi-Fi adapter, 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 flash drive
USB flash drive
, memory card reader , digital audio player , digital camera , external drive

09h Device 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 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 device

FEh Interface Application-specific IrDA Bridge, Test "> A flash drive , a typical USB
USB
mass-storage device Circuit board from a USB 3.0 external 2.5-inch SATA
SATA
HDD enclosure See also: USB mass storage device class , Disk enclosure , and External hard disk drive

USB
USB
implements connections to storage devices using a set of standards called the USB mass storage device class (MSC or UMS). This was at first intended for traditional magnetic and optical drives and 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 with a USB adapter is particularly advantageous for maintaining the integrity and non-corruptible, pristine state of the booting medium.

Though most 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. Buses such as Parallel ATA (PATA or IDE), Serial ATA (SATA), or SCSI
SCSI
fulfill that role in PC class computers. However, USB has one important advantage, in that it is possible to install and remove devices without rebooting the computer (hot-swapping ), making it useful for mobile peripherals, including drives of various kinds (given SATA
SATA
or SCSI
SCSI
devices may or may not support hot-swapping).

Firstly conceived and still used today for optical storage devices ( 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 (in practice about 30 MB/s for USB
USB
2.0 and potentially 400 MB/s or more for USB
USB
3.0). These external drives typically include a "translating device" that bridges between a drive's interface to a USB
USB
interface port. Functionally, the drive appears to the user much like an internal drive. Other competing standards for external drive connectivity include e SATA
SATA
, ExpressCard , 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 clients) with no need to install them on the host computer.

MEDIA TRANSFER PROTOCOL

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 which was 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

Main article: USB human interface device class

Joysticks, keypads, tablets and other human-interface devices (HIDs) are also progressively migrating from MIDI, and PC game port connectors to USB.

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. These devices present two HID endpoints to the system and use a microcontroller to perform bidirectional data translation between the two standards.

DEVICE FIRMWARE UPGRADE

_Device 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 for firmware bugfixes to be deployed. 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.

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 .

CONNECTORS

CONNECTOR PROPERTIES

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.

Receptacles And Plugs

The connector mounted on the host or device is called the _receptacle_, and the connector attached to the cable is called the _plug_. The official USB
USB
specification documents also periodically define the term _male_ to represent the plug, and _female_ to represent the receptacle.

Usability And Orientation

USB
USB
extension cable

By design, it is difficult to insert a USB
USB
plug into its receptacle incorrectly. The USB
USB
specification states that the required USB
USB
icon must be embossed on the "topside" of the USB
USB
plug, which "...provides easy user recognition and facilitates alignment during the mating process." The specification also shows that the "recommended" "Manufacturer's logo" ("engraved" on the diagram but not specified in the text) is on the opposite side of the USB
USB
icon. The specification further states, "The USB
USB
Icon is also located adjacent to each receptacle. Receptacles should be oriented to allow the icon on the plug to be visible during the mating process." However, the specification does not consider the height of the device compared to the eye level height of the user, so the side of the cable that is "visible" when mated to a computer on a desk can depend on whether the user is standing or kneeling.

While connector interfaces can be designed to allow plugging with either orientation, the original design omitted such functionality to decrease manufacturing costs. The reversible type-C plug is an addition to the USB 3.1 specification comparable in size to the Micro-B SuperSpeed connector.

Only moderate force is needed to insert or remove a USB
USB
cable. USB cables and small USB
USB
devices are held in place by the gripping force from the receptacle (without need of the screws, clips, or thumb-turns other connectors have required).

Power-use Topology

The standard connectors were deliberately intended to enforce the directed topology of a USB
USB
network: type-A receptacles on host devices that supply power and type-B receptacles on target devices that draw power. This prevents users from accidentally connecting two USB
USB
power supplies to each other, which could lead to short circuits and dangerously high currents, circuit failures, or even fire. USB
USB
does not support cyclic networks and the standard connectors from incompatible USB
USB
devices are themselves incompatible.

However, some of this directed topology is lost with the advent of multi-purpose USB
USB
connections (such as USB On-The-Go in smartphones, and USB-powered Wi-Fi routers), which require A-to-A, B-to-B, and sometimes Y/splitter cables. See the USB On-The-Go connectors section below for a more detailed summary description.

Durability

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, the mini- USB
USB
receptacle increases this to 5,000 cycles, and the newer Micro- USB
USB
and USB-C receptacles are both designed for a minimum rated lifetime of 10,000 cycles of insertion and removal. 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.

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 sheath.

In all USB
USB
connectors, the construction always ensures that the external sheath on the plug makes contact with its counterpart in the receptacle before any of the four connectors within make electrical contact. The external metallic sheath is typically connected to system ground, thus dissipating damaging static charges. This enclosure design also provides a degree of protection from electromagnetic interference to the USB
USB
signal while it travels through the mated connector pair (the only location when the otherwise twisted data pair travels in parallel). In addition, because of the required sizes of the power and common connections, they are made after the system ground but before the data connections. This type of staged make-break timing allows for electrically safe hot-swapping.

Compatibility

The USB
USB
standard specifies relatively loose tolerances for compliant USB
USB
connectors to minimize physical incompatibilities in connectors from different vendors. To address a weakness present in some other connector standards, the USB
USB
specification also defines limits to the size of a connecting device in the area around its plug. This was done to prevent a device from blocking adjacent ports due to the size of the cable strain relief mechanism (usually molding integral with the cable outer insulation) at the connector. Compliant devices must either fit within the size restrictions or support a compliant extension cable that does.

In general, USB
USB
cables have only plugs on their ends, while hosts and devices have only receptacles. Hosts almost universally have Type-A receptacles, while devices have one or another Type-B variety. Type-A plugs mate only with Type-A receptacles, and the same applies to their Type-B counterparts; they are deliberately physically incompatible. However, an extension to the USB
USB
standard specification called USB On-The-Go (OTG) allows a single port to act as either a host or a device, which is selectable by the end of the cable that plugs into the receptacle on the OTG-enabled unit. Even after the cable is hooked up and the units are communicating, the two units may "swap" ends under program control. This capability is meant for units such as PDAs in which the USB
USB
link might connect to a PC's host port as a device in one instance, yet connect as a host itself to a keyboard and mouse device in another instance.

CONNECTOR TYPES

Various USB
USB
connectors along a centimeter ruler for scale (1 cm is 3⁄8 in). From left to right:

* Micro-B plug * UC-E6 * Mini-B plug * type-A receptacle * 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.

There are several types of USB
USB
connector, including some that have been added while the specification progressed. The original USB specification detailed standard-A and standard-B plugs and receptacles; the B connector was necessary so that cabling could be plug ended at both ends and still prevent users from connecting one computer receptacle to another. The first engineering change notice to the USB
USB
2.0 specification added Mini-B plugs and receptacles.

The data pins in the standard plugs are actually recessed in the plug compared to the outside power pins. This permits the power pins to connect first, preventing data errors by allowing the device to power up first and then establish the data connection. Also, some devices operate in different modes depending on whether the data connection is made.

To reliably enable a charge-only feature, modern USB
USB
accessory peripherals now include charging cables that provide power connections to the host port but no data connections, and both home and vehicle charging docks are available that supply power from a converter device and do not include a host device and data pins, allowing any capable USB
USB
device to charge or operate from a standard USB
USB
cable.

In a charge-only cable, the data wires are shorted at the device end. These wires are usually green and white. If these wires are left as-is, the device will often reject the charger as unsuitable.

Standard Connectors

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, will be terminated 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.

The spring contacts in the connectors eventually relax and wear out with repeated cycles of plugging and unplugging. The lifetime of a type-A plug is approximately 1,500 connect/disconnect cycles.

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).

Mini Connectors

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

For smaller devices such as digital cameras , smartphones , and tablet computers , various smaller connectors have been used – the USB-standard first introduced the Mini- USB
USB
connectors.

Mini- USB
USB
connectors were introduced together with USB
USB
2.0 in April 2000 – however the Mini-A connector and the Mini-AB receptacle connector are deprecated (i.e. de-certified, but standardized) since May 2007. Mini-B connectors are still supported, but are not On-The-Go-compliant; 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

Micro-A plug Micro-B plug

Micro- USB
USB
connectors, which were announced by the USB-IF on 4 January 2007, 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).

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. While some of the devices and cables still use the older Mini variant, the newer Micro connectors are widely adopted, and as of December 2010 they are the most widely used.

The Micro plug design is rated for at least 10,000 connect-disconnect cycles, which is more than the Mini plug design. 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 Cables and Connectors Specification_ details the mechanical characteristics of Micro-A plugs , Micro-AB receptacles (which accept both Micro-A and Micro-B plugs), and Micro-B plugs and receptacles, along with a standard-A receptacle to Micro-A plug adapter.

OMTP Standard

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.

Micro- USB
USB
was embraced as the "Universal Charging Solution" by the International Telecommunication Union (ITU) in October 2009.

In Europe, micro- USB
USB
became the defined common external power supply (EPS) for use with smartphones sold in the EU, 14 of the world's largest mobile phone manufacturers signed the EU's common EPS Memorandum of Understanding (MoU). 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 . according to the CEN , CENELEC and ETSI .

Non-standard Cables

Non-standard reversible micro-B plug connector

A reversible micro connector plug that can be connected to existing Micro-B sockets has been developed by Winner Gear, crowdfunded on Indiegogo , with no functional enhancement to the USB. And there are many USB-A to reversible Micro-B cable manufacturer offerings, as well as USB On-The-Go (OTG) to reversible Micro-B cables.

USB 3.0 Connectors And Backward Compatibility

USB 3.0 Micro-B SuperSpeed plug See also: USB 3.0 § Connectors

USB 3.0 introduced Type-A SuperSpeed plugs and receptacles as well as micro-sized Type-B SuperSpeed plugs and receptacles. The 3.0 receptacles are backward-compatible with the corresponding pre-3.0 plugs.

USB 3.0 and USB
USB
1.0 Type-A plugs and receptacles are designed to interoperate. In order to achieve USB
USB
3.0's SuperSpeed (and SuperSpeed+ for USB 3.1 Gen 2), 5 extra pins are added to the unused area of the original 4 pin USB
USB
1.0 design, making USB 3.0 Type-A plugs and receptacles backward compatible to those of USB
USB
1.0. USB Micro-B USB
USB
2.0 vs USB
USB
Micro-B SuperSpeed ( USB
USB
3.0)

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 Type-C plug can also be used). The 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 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
USB
3.0 B type plug

USB On-The-Go Connectors

Main article: 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 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 found 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.

USB-C

The USB-C plug

USB-C cable USB-C port on an Apple MacBook
MacBook
Main article: USB Type-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 and defines a new small reversible-plug connector for USB devices. 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.

The 24-pin double-sided connector provides four power-ground pairs, two differential pairs for USB
USB
2.0 data bus (though only one pair is implemented in a Type-C cable), four pairs for SuperSpeed data bus (only two pairs are used in 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. 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.

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 2.0 specification. 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 cable for direct device-to-host transmission of alternate data protocols. The four high-speed lanes, two sideband pins, and‍—‌for dock, detachable device and permanent cable applications only‍—‌two USB
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

USB
USB
plugs fit one receptacle with notable exceptions for USB On-The-Go "AB" support and the general backward compatibility of USB 3.0 as shown.

USB
USB
connectors mating matrix (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 matrix 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
USB
specifications. Other combinations of connectors are not compliant. There do exist A-to-A assemblies, referred to as cables (such as the Easy Transfer Cable
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. Note: Mini-B is not deprecated, but less and less used since the arrival of Micro-B.

PINOUTS

See also: USB 3.0 § Pinouts

USB
USB
is a serial bus, using four shielded wires for the USB
USB
2.0 variant: two for power (VBUS and GND), and two for differential data signals (labelled as D+ and D− in pinouts ). Non-Return-to-Zero Inverted (NRZI) encoding scheme is used for transferring data, with a sync field to synchronize the host and receiver clocks. D+ and D− signals are transmitted on a differential pair , providing half-duplex data transfers for USB
USB
2.0. 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 host/client identification.

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
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. MICRO-B SUPERSPEED PLUG

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

Type-A and -B pinout PIN NAME WIRE COLOR 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 DESCRIPTION

1 VBUS Red +5 V

2 D− White Data−

3 D+ Green Data+

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

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

5 GND Black Signal ground

Proprietary Connectors And Formats

Manufacturers of personal electronic devices might not include a USB standard connector on their product for technical or marketing reasons. 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.

*

HTC
HTC
ExtMicro USB
USB
port and connector *

Nokia
Nokia
Pop-Port connector *

An Apple Lightning -to- USB adapter and captive USB
USB
cable

COLORS

An orange charge-only USB
USB
port on a front panel 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 contacts fitted. A USB
USB
AC adaptor with a green USB
USB
connector supporting Qualcomm Quick Charge 2.0.

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 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.

CABLING

_ 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 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 data transmission, cables contain twice as many wires and are thus larger in diameter.

The USB
USB
1.1 standard specifies that a standard cable can have a maximum length of 3 metres (9 ft 10 in) with devices operating at full speed (12 Mbit/s), and a maximum length of 5 metres (16 ft 5 in) with devices operating at low speed (1.5 Mbit/s).

USB
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 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. The USB
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).

POWER

USB
USB
power standards SPECIFICATION CURRENT VOLTAGE POWER

Low-power device 100 mA 5 V 0.50 W

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

High-power device 500 mA 5 V 2.5 W

High-power SuperSpeed ( USB
USB
3.0) device 900 mA 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 micro-format 3 A 20 V 60 W

Power Delivery standard format or Type-C 5 A 20 V 100 W

* ^ Up to five unit loads; with non- SuperSpeed devices, one unit load is 100 mA. * ^ Up to six unit loads; with SuperSpeed devices, one unit load is 150 mA. * ^ _A_ _B_ _C_ Either SuperSpeed or non-SuperSpeed. * ^ Requires PD 5 A cable.

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

USB
USB
supplies bus power across VBUS and GND at a nominal voltage 5 V ± 5%, at supply, to power USB
USB
devices. Power is sourced solely from upstream devices or hosts, and is consumed solely by downstream devices. USB
USB
provides for various voltage drops and losses in providing bus power. As such, the voltage at the hub port is specified to be in the range 7000500000000000000♠5.00+0.25 −0.60 V by USB
USB
2.0, and 7000500000000000000♠5.00+0.25 −0.55 V by USB
USB
3.0. It is specified that devices' configuration and low-power functions must operate down to 4.40 V at the hub port by USB
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
USB
3.0.

There are limits on the power a device may draw, stated in terms of a _unit load_, which is 100 mA, or 150 mA for SuperSpeed devices. There are low-power and high-power devices. Low-power devices may draw at most 1 unit load, and all devices must act as low-power devices when, starting out as, unconfigured. High-power devices draw at least 1 unit load and at most 5 unit loads (500 mA), or 6 unit loads (900 mA) for SuperSpeed devices. A high-powered device must be configured, and may only draw as much power as specified in its configuration. 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 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, 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 2 USB
USB
plugs (1 for power and data, the other for only power), so as to draw power as 2 devices. 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 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."

USB
USB
BATTERY CHARGING

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
USB
Battery Charging defines a new port type, the _charging port_, as opposed to the _standard downstream port_ (SDP) of the base specification. Charging ports are divided into 2 further types: the _charging downstream port_ (CDP), which has data signals, and the _dedicated charging port_ (DCP), which does not. Dedicated charging ports can be found on USB
USB
power adapters that convert utility power or another power source (e.g., a car's electrical system) to run attached devices and battery packs. On a host (such as a laptop computer) with both standard and charging USB
USB
ports, the charging ports should be labeled as such.

The charging device identifies the type of port through non-data signalling on the D+ and D− signals immediately after attach. A DCP simply has to place a resistance not exceeding 200 Ω across the D+ and D− signals.

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 1.5A of current. The charging port may apply current limiting or shut down completely, but must not apply limiting below 0.5A, and must not shut down below 1.5A or before the voltage drops to 2V.

These bus power currents being much higher than cables were designed for, though not unsafe, cause a larger voltage between the ends of the ground signal, significantly reducing noise margins causing problems with High Speed signalling. Battery Charging 1.1 specifies that charging devices must dynamically limit bus power current draw during High Speed signalling; 1.2 simply specifies that charging devices and ports must be designed to tolerate the higher ground voltage difference in High Speed signalling.

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.

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. When D+ = 2.8 V and D− = 2.0 V, the device may pull up to 2 A of current.

Accessory Charging Adaptors (ACA)

Portable devices having an 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 and space requirement) prevents this. _Accessory charging adapters (ACA)_ are devices which allow a charging power to be injected into an 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 signalling. 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 signalled 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.

POWER DELIVERY (PD)

See also: List of 60W/100W USB chargeable laptops

USB
USB
PD rev. 1 source profiles PROFILE +5 V +12 V +20 V

0 Reserved

1 2.0 A, 10 W No No

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 source power rules Source output power (W) CURRENT, AT: (A)

+5 V +9 V +15 V +20 V

0.5–15 0.1–3.0 No No No

15–27 3.0 (15 W) 1.7–3.0

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 (PD) specification, 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). In all cases, both host-to-device and device-to-host configurations are supported.

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.

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 revision 2.0 specification has been released as part of the USB 3.1 suite. 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 . 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 Revision 2.0 Version 1.2, the six fixed power profiles for power sources have been deprecated. USB
USB
PD Power Rules replace power profiles, defining four normative voltage levels at 5V, 9V, 15V, and 20V. Instead of six fixed profiles, power supplies may support any maximum source output power from 0.5W to 100W.

Upcoming USB Power Delivery 3.0 specification defines new power rules based on supplied wattage. Programmable power supply protocol allows granular control over VBUS power in 10 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.

As of April 2016 , there are silicon controllers available from several sources (TI, Cypress) and several others. Power supplies bundled with Type-C based laptops from Apple, Google, HP, Dell, and Razer support USB
USB
PD. In addition, accessories from third party vendors including Anker, Belkin , iVoler and Innergie support USB PD 2.0 at multiple voltages. There are several PD aware projects such as the USB-PD Sniffer that are PD aware. ASUS also make a fully Power Delivery compliant adapter card the USB 3.1 UPD PANEL

SLEEP-AND-CHARGE PORTS

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. This feature has also been implemented on some laptop docking stations allowing device charging even when no laptop is present.

Sleep-and-charge USB
USB
ports may be found colored differently than regular ports, mostly red or yellow, 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_, while Toshiba calls it _USB Sleep-and-Charge_. On Acer Inc. and Packard Bell laptops, sleep-and-charge USB
USB
ports are marked with a non-standard symbol (the letters _USB_ over a drawing of a battery); the feature is simply called _Power-off USB_. On some laptops such as Dell and Apple MacBook
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.

MOBILE DEVICE CHARGER STANDARDS

In China

The Micro- USB
USB
interface is commonly found on chargers for mobile phones Australian and New Zealand power socket with USB charger socket

As of 14 June 2007 , 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. This was the first standard to use the convention of shorting D+ and D−.

OMTP/GSMA Universal Charging Solution

In September 2007, the Open Mobile Terminal Platform group (a forum of mobile network operators and manufacturers such as Nokia
Nokia
, Samsung , Motorola
Motorola
, Sony Ericsson and LG ) announced that its members had agreed on Micro- USB
USB
as the future common connector for mobile devices.

The GSM Association (GSMA) followed suit on 17 February 2009, and on 22 April 2009, this was further endorsed by the CTIA – The Wireless
Wireless
Association , with the 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."

EU Smartphone
Smartphone
Power Supply Standard

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 standard and is similar to the GSMA/OMTP and Chinese charging solutions. In January 2011, the International Electrotechnical Commission (IEC) released its version of the (EU's) common EPS standard as IEC 62684:2011.

NON-STANDARD DEVICES

_ This section DOES NOT CITE ANY SOURCES . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (October 2011)_ _(Learn how and when to remove this template message )_

USB-powered mini fans USB
USB
vacuum cleaner novelty device

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 used 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.

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
USB
decorations _. 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 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. Barnes this is 70% of the total available bus bandwidth. For USB
USB
3.0, typical write speed is 70–90 MB/s, while read speed is 90–110 MB/s. 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.

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". 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
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
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. Connectors are identical for USB
USB
2.0 and USB
USB
1.x. * SUPERSPEED (SS) rate of 5.0 Gbit/s. The written USB
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, and the first products using the USB 3.0 specification arrived in January 2010. USB 3.0 connectors are generally backward compatible, but include new wiring and full duplex operation.

Transaction Latency

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. High-speed (480 Mbit/s) uses transactions within each micro frame (125 µs) where using 1-byte interrupt packet results in a minimal response time of 940 ns. 4-byte interrupt packet results in 984 ns.

ELECTRICAL SPECIFICATION

USB
USB
signals are transmitted using differential signalling on a twisted-pair data cable with 90 Ω ± 15% characteristic impedance .

* 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 (SS) adds two additional pairs of shielded twisted wire (and new, mostly compatible expanded connectors). These are dedicated to full-duplex SuperSpeed operation. The half-duplex lines are still used for configuration.

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. Originally, this was a _B_ connector, preventing erroneous loop connections, but additional upstream connectors were specified, and some cable vendors designed and sold cables that permitted erroneous connections (and potential damage to circuitry). USB
USB
interconnections are not as fool-proof or as simple as originally intended.

SIGNALLING STATE

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

The following terminology is used to assist in the technical discussion regarding USB
USB
PHY signalling.

SIGNAL LINE TRANSITION STATE DESCRIPTION USB
USB
1.x Low Speed

(1.5 kΩ pullup on D−) USB
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 pullup 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
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 just the opposite polarity to the _J_ state.

Line State (covering USB
USB
1.x And 2.x)

LINE STATE/SIGNAL DESCRIPTION USB
USB
1.X LOW SPEED USB
USB
1.X FULL SPEED USB
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 >= 2us SE0 >= 2us SE0 >= 2us

Connect USB
USB
device pullups on D+ or D- will wakes the host from detached line state.

This will start 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 >= 2.5ms SE0 >= 2.5ms

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 >= 3ms J >= 3ms

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

Resume (device) device wants to wake up.

(Must be in idle for at least 5ms) device drives K >= 1ms

host then sends a resume signal device drives K >= 1ms

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

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 is enough signal transitions for clock recovery to occur in the bitstream , bit stuffing techniques is applied to the data stream. This is via inserting extra 0 bit into the data stream after any appearance of six consecutive 1 bits (Thus ensuring that there is a 0 bit to cause a transmission state transition). Seven consecutive received 1 bits is always an error. For USB
USB
3.0, additional data transmission encoding was included to deal with the higher speed rate that was required by the newer standard.

Transmission Example On A USB
USB
1.1 Full Speed Device

Example of a Negative Acknowledge packet transmitted by USB
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.

* SYNCHRONISATION 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 frame. For high bandwidth USB, the packet begins with a 32-bit synchronization sequence. * END OF PACKET (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
USB
2.0 SPEED NEGOTIATION

USB
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
USB
2.0 High Speed capable first connects as an 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 uses wiring separate and additional to that used by USB
USB
2.0 and USB
USB
1.x, such bandwidth negotiation is not required.

Clock tolerance is 480.00±0.24 Mbit/s, 12.00±0.03 Mbit/s, 1.50±0.18 Mbit/s.

Though high bandwidth devices are commonly referred to as " USB
USB
2.0" and advertised as "up to 480 Mbit/s," not all USB
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
USB
3.0

USB
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. SSC clock and 300 ppm precision is used. Packet headers are protected with CRC-16, while data payload is protected with CRC-32. Power up to 3.6 W may be used. One unit load in superspeed mode is equal to 150 mA.

PROTOCOL LAYER

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
USB
2.0) split transaction

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

Special 1100 0011 1100 PRE Low-bandwidth USB
USB
preamble

Handshake ERR Split transaction error ( USB
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
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
USB
2.0)

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

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

HANDSHAKE PACKETS

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 that represent the packet type twice, in a single PID byte using complemented form. 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.

USB
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.

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

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
USB
2.0 devices receive seven additional SOF tokens per frame, each introducing a 125 µs "microframe" (60000 high-bandwidth bit times each).

USB
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 to be unwilling to accept it. 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

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

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

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 (0B) * EP : End Point Type ( 00 = Control ) ( 01 = Isochronous ) ( 10 = bulk ) ( 11 = interrupt )

DATA PACKETS

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), 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.

When a device is reset with a SETUP packet, it expects an 8-byte DATA0 packet next.

USB
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 bits per 125 µs micro frame (8,192 kbit/s).

PRE PACKET (TELLS HUBS TO TEMPORARILY SWITCH TO LOW SPEED MODE)

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 will misinterpret a high or full speed signal from the host.

To eliminate this danger, if a USB hub detects a mix of highspeed or full speed and low speed devices, it will by default disable communication to low speed device unless requested to switch to low speed mode. On reception of a PRE packet however, it will temporarily re-enable 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 will tell 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

OUT TRANSACTION

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

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

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

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

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.

What this allows the host to do, is 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 will perform another control transfer exchange, but instead to set the address of the USB
USB
device to a new ADDRx .

AUDIO STREAMING

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 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.

COMPARISONS WITH OTHER CONNECTION METHODS

A variety of USB
USB
cables for sale in Hong Kong

FIREWIRE

At first, USB
USB
was considered a complement to 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 and USB include:

* USB
USB
networks use a tiered-star topology, while IEEE 1394 networks use a tree topology. * USB
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. USB 3.0 allows for device-initiated communications towards the host. A 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 network, any capable node can control the network. * USB
USB
runs with a 5 V power line, while FireWire in current implementations supplies 12 V and theoretically can supply up to 30 V. * Standard 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
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 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 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 Hi-Bandwidth in real-use, especially in high-bandwidth use such as external hard drives. The newer FireWire 800 standard is twice as fast as FireWire 400 and faster than USB
USB
2.0 Hi-Bandwidth both theoretically and practically. 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 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.

ETHERNET

The IEEE 802.3af 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
USB
2.0, which provides 2.5 W with a maximum cable length of 5 meters. This has made PoE popular for 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. 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.

MIDI

Digital musical instruments are another example where USB
USB
is competitive for low-cost devices. However 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

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
USB
3.1, announced on 31 July 2013). A device connected by e SATA
SATA
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 to 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

Thunderbolt combines PCI Express
PCI Express
and 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.

Thunderbolt 2 uses link aggregation to combine the two 10 Gbit/s channels into one bi-directional 20 Gbit/s channel.

Thunderbolt 3 is announced to use USB Type-C connectors. Thunderbolt 3 has one 40 Gbit/s channel.

INTEROPERABILITY

Main article: USB adapter

Various protocol converters are available that convert USB
USB
data signals to and from other communications standards.

RELATED STANDARDS

The Wireless
Wireless
USB
USB
logo

The USB Implementers Forum is working on a wireless networking standard based on the USB
USB
protocol. Wireless
Wireless
USB
USB
is a cable-replacement technology, and uses ultra-wideband wireless technology for data rates of up to 480 Mbit/s.

USB
USB
2.0 High-Speed Inter-Chip (HSIC) is a chip-to-chip variant of USB 2.0 that eliminates the conventional analog transceivers found in normal USB. It was adopted as a standard by the USB
USB
Implementers Forum in 2007. The HSIC physical layer uses about 50% less power and 75% less board area compared to traditional USB
USB
2.0. HSIC uses two signals at 1.2 V and has a throughput of 480 Mbit/s. Maximum PCB trace length for HSIC is 10 cm. It does not have low enough latency to support RAM memory sharing between two chips.

The USB 3.0 successor of HSIC is called SuperSpeed Inter-Chip (SSIC).

SEE ALSO

* Computing portal * Electronics portal

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

NOTES

REFERENCES

* ^ "82371FB (PIIX) and 82371SB (PIIX3) PCI ISA IDE Xcelerator" (PDF). Intel. May 1996. Retrieved 2016-03-12. * ^ _A_ _B_ " USB
USB
‘A’ Plug Form Factor Revision 1.0" (PDF). USB Implementers Forum. 23 March 2005. p. 1. Retrieved 2017-06-04. 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, 1995-12-31, retrieved 2011-12-12 * ^ "Sony Playstation 3 60 GB, Sony Playstation 4 Pro, and Xbox One S", Reviews, _CNet_ * ^ _A_ _B_ " USB
USB
connector guide". C2G. Retrieved 2013-12-02. * ^ _A_ _B_ _C_ _D_ _Universal Serial Bus Cables and Connectors Class Document_ (PDF), Revision 2.0, USB
USB
Implementers Forum, August 2007, p. 6, retrieved 2014-08-17 * ^ _A_ _B_ "Why was Mini- USB
USB
deprecated in favor of Micro-USB?". _Stack exchange_. 2011. Retrieved 2013-12-03. * ^ _Icon design recommendation for Identifying USB
USB
2.0 Ports on PCs, Hosts and Hubs_ (PDF), USB
USB
. * ^ Janssen, Cory. "What is a Universal Serial Bus (USB)?". _Techopedia_. Retrieved 2014-02-12. * ^ _Ajay Bhatt: Fellow_ (biography), Intel
Intel
* ^ Rogoway, Mark (2009-05-09). " Intel
Intel
ad campaign remakes researchers into rock stars". _ The Oregonian _. Retrieved 2009-09-23. * ^ _A_ _B_ Pan, Hui; Polishuk, Paul (eds.). _1394 Monthly Newsletter_. Information Gatekeepers. pp. 7–9. GGKEY:H5S2XNXNH99. Retrieved 2012-10-23. * ^ 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". _Mac world_. Aug 2007. * ^ _A_ _B_ " Compaq hopes to follow the iMac". Archived from the original on 22 October 2006. * ^ _A_ _B_ "The PC Follows iMac\'s Lead". 1999. Text " work ≠ Business week " ignored (help ) * ^ _A_ _B_ _Popular Mechanics: Making Connections_. Hearst Magazines. February 2001. p. 59. ISSN 0032-4558 . * ^ _Universal Serial Bus Specification Revision 3.0: 3.1_ (Zip). 9 September 2011. p. 41 (3–1). Retrieved 2011-10-14. 08-Sep-2012 * ^ _Universal Serial Bus Specification Revision 3.0: 1.6_ (Zip). 9 September 2011. p. 31 (1–3). Retrieved 2011-10-14. * ^ _A_ _B_ " USB 3.0 SuperSpeed gone wild at CES 2010, trumps even your new SSD". 9 January 2010. Retrieved 2011-02-20. * ^ " USB 3.0 Finally Arrives". 11 January 2010. Retrieved 2011-02-20. * ^ " SuperSpeed USB
USB
3.0: More Details Emerge". _PC world_. 6 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. December 8, 2014. * ^ _A_ _B_ "What\'s the Difference Between USB
USB
1.0 and USB
USB
2.0? - Quality Logo Products, Inc.". Retrieved 30 December 2016. * ^ _A_ _B_ _C_ http://www.usb.org/developers/ssusb/USB_3_1_Language_Product_and_Packaging_Guidelines_FINAL.pdf * ^ " USB
USB
3.2 will make your cables twice as fast". _arstechnica.com_. Retrieved 27 July 2017. * ^ "5.5.4". _Universal Serial Bus Specification_ (PDF) (Technical report). 2000. p. 40. v2.0. * ^ " USB
USB
Implementers Forum". * ^ _A_ _B_ _C_ "Battery Charging v1.2 Spec and Adopters Agreement" (Zip). USB
USB
Implementers Forum. 7 December 2010. Retrieved 2014-10-05. * ^ "USB" (PDF) (Press release). Implementers Forum. 2008-11-17. Retrieved 2010-06-22. * ^ " USB 3.0 Technology" (PDF). HP . 2012. Retrieved 2014-01-02. * ^ "Universal Serial Bus 3.0 Specification" (PDF). USB Implementers Forum. 2008-11-12. Retrieved 2012-12-29. * ^ " SuperSpeed USB
USB
( USB
USB
3.0) Performance to Double with New Capabilities" (PDF) (Press release). Implementers Forum. 2013-01-06. * ^ " SuperSpeed USB
USB
10 Gbps – Ready for Development" (PDF) (Press release). Hillsboro, Ore. July 31, 2013. Archived from the original (PDF) on 2016-01-27. * ^ " SuperSpeed USB
USB
10 Gbps - Ready for Development". Rock Hill Herald. Archived from the original on 11 October 2014. Retrieved 2013-07-31. * ^ " Synopsys Demonstrates Industry\'s First SuperSpeed USB
USB
10 Gbps Platform-to-Platform Host-Device IP Data Transfer" (Press release). Mountain View, California : Synopsys . 2013-12-10. Retrieved 2013-12-23. As measured by the Ellisys USB
USB
Explorer Protocol Analyzer, the IP realized 10 Gbps USB 3.1 Gen 2 effective data rates of more than 900 MBps between two Synopsys HAPS-70 FPGA-based prototyping systems while using backward compatible USB
USB
connectors, cables and software. * ^ _Universal Serial Bus Specification Revision 2.0_ (Zip ). 11 October 2011. pp. 13; 30; 256. Retrieved 2012-09-08. * ^ _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 (2009-05-20). "Isochronous Protocol" (PDF). _usb.org_. Retrieved 2014-11-21. * ^ "Class Codes". USB
USB
Implementers Forum. . * ^ 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 Upgrade, Version 1.1" (PDF). USB
USB
Implementers Forum. 2004-08-05. pp. 8–9. Retrieved 2014-09-08. * ^ _Universal Serial Bus 3.0 Specification_,4.4.11 "Efficiency" * ^ "100 Portable Apps for your USB
USB
Stick (both for Mac and Win)". Retrieved 2008-10-30. * ^ "Skype VoIP USB
USB
Installation Guide". Retrieved 2008-10-30. * ^ "PS/2 to USB
USB
Keyboard and Mouse Adapter". * ^ "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 Upgrade tool". _fedoraproject.org_. Retrieved 2014-09-08. * ^ Karsten Nohl; Sascha Krißler; Jakob Lell (2014-08-07). "BadUSB – On accessories that turn evil" (PDF). _srlabs.de_. Retrieved 2014-09-08. * ^ _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. Retrieved 2011-07-26. CS1 maint: Uses authors parameter (link ) * ^ " USB
USB
2.0 Specification Engineering Change-USB.org" (PDF). USB Flash Drive Alliance. Retrieved 2014-12-29. * ^ _A_ _B_ _C_ Cite error: The named reference cabcomm20 was invoked but never defined (see the help page ). * ^ Howse, Brett. " USB Type-C Connector Specifications Finalized". _AnandTech_. Anadtech. Retrieved 24 April 2017. * ^ _A_ _B_ _C_ "Universal Serial Bus Cables and Connectors Class Document Revision 2.0" (PDF). usb.org. August 2007. Retrieved 2013-12-03. * ^ Quinnell, Richard A (24 October 1996). "USB: a neat package with a few loose ends". _EDN Magazine_. Reed. Retrieved 2013-02-18. * ^ "What is the Difference between USB
USB
Type A and USB
USB
Type B Plug/Connector?". * ^ "What is the Life Cycle of a USB
USB
Flash Drive?". Get USB. 2007-03-08. Retrieved 2011-12-12. * ^ " USB
USB
2.0 Specification Engineering Change Notice (ECN) #1: Mini-B connector" (PDF). USB-IF Developers Area. 2000-10-20. Retrieved 2014-12-11. * ^ _A_ _B_ " Deprecation of the Mini-A and Mini-AB Connectors" (PDF) (Press release). USB
USB
Implementers Forum. 2007-05-27. Retrieved 2009-01-13. * ^ "ID Pin Resistance on Mini B-plugs and Micro B-plugs Increased to 1 Mohm". USB
USB
IF Compliance Updates. December 2009. Retrieved 2010-03-01. * ^ "Mobile phones to adopt new, smaller USB
USB
connector" (PDF) (Press release). USB
USB
Implementers Forum. 2007-01-04. Retrieved 2007-01-08. * ^ _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_. * ^ _A_ _B_ "Universal Serial Bus Micro- USB
USB
Cables and Connectors Specification to the USB
USB
2.0 Specification, Revision 1.01" (PDF). USB Implementers Forum. 2007-04-07. Archived from the original (Zip) on 2007-04-08. Retrieved 2010-11-18. 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. 2009-10-22. Retrieved 2009-11-04. * ^ "Commission welcomes new EU standards for common mobile phone charger". _Press Releases_. Europa. 2010-12-29. Retrieved 2011-05-22. * ^ _New EU standards for common mobile phone charger_ (press release), Europa * ^ _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 * ^ "Nice Micro- USB adapter Apple, now sell it everywhere", _Giga om_, 5 October 2011 * ^ "Apple\'s Lightning to Micro- USB adapter now available in US, not just Europe anymore", _Engadget_, 2012-11-03 * ^ _A_ _B_ Howse, Brett (August 12, 2014). " USB Type-C Connector Specifications Finalized". Retrieved December 28, 2014. * ^ Hruska, Joel (March 13, 2015). " USB-C vs. USB
USB
3.1: What’s the difference?". ExtremeTech. Retrieved April 9, 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 Type-C Connector". Archived from the original on 29 December 2014. Retrieved 29 December 2014. * ^ Smith, Ryan (September 22, 2014). "DisplayPort Alternate Mode for USB Type-C Announced - Video, Power, & Data All Over Type-C". _ AnandTech _. 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. Retrieved 2014-06-23. * ^ "Proprietary Cables vs Standard USB". _anythingbutipod.com_. 2008-04-30. Retrieved 2013-10-29. * ^ Lex Friedman (2013-02-25). "Review: Logitech\'s Ultrathin mini keyboard cover makes the wrong tradeoffs". _macworld.com_. Retrieved 2013-10-29. * ^ Qualcomm Certified Nekteck Quick Charge 2.0 54W 4 Ports 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_. Retrieved 2014-05-19. * ^ "What is the USB 3.0 Cable Difference". Hantat. 2009-05-18. Retrieved 2011-12-12. * ^ " USB
USB
Cable Length Limitations" (PDF). cablesplususa.com. 2010-11-03. Retrieved 2014-02-02. * ^ "Cables and Long-Haul Solutions". _ USB
USB
FAQ_. USB.org. Retrieved 2014-02-02. * ^ " USB
USB
Frequently Asked Questions". USB
USB
Implementers Forum. Retrieved 2010-12-10. * ^ Axelson, Jan. " USB 3.0 Developers FAQ". Retrieved 2016-10-20. * ^ "7.3.2 Bus Timing/Electrical Characteristics". _Universal Serial Bus Specification_. USB.org. * ^ "USB.org". USB.org. Retrieved 2010-06-22. * ^ "Universal Serial Bus 1.1 Specification" (PDF). _cs.ucr.edu_. 1998-09-23. pp. 150, 158. Retrieved 2014-11-24. * ^ "Universal Serial Bus 2.0 Specification, Section 7.2.1.3 Low-power Bus-powered Functions" (ZIP). _usb.org_. 2000-04-27. Retrieved 2014-01-11. * ^ "Universal Serial Bus 2.0 Specification, Section 7.2.1.4 High-power Bus-powered Functions" (ZIP). _usb.org_. 2000-04-27. Retrieved 2014-01-11. * ^ "Roundup: 2.5-inch Hard Disk Drives with 500 GB, 640 GB and 750 GB Storage Capacities (page 17)". xbitlabs.com. 2010-06-16. Retrieved 2010-07-09. * ^ "I have the drive plugged in but I cannot find the drive in "My Computer", why?". hitachigst.com. Retrieved 2012-03-30. * ^ "USB-IF Compliance Updates". Compliance.usb.org. 2011-09-01. Retrieved 2014-01-22. * ^ _A_ _B_ _C_ _D_ "Battery Charging Specification, Revision 1.2". USB
USB
Implementers Forum. 7 December 2010. Retrieved 2016-03-29. * ^ Section 1.4.5, pg. 2; and Table 5-3 "Resistances", pg. 45 * ^ "Battery Charging Specification, Revision 1.1". 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 * ^ _Modify a cheap USB
USB
charger to feed an iPod, iPhone_, 2013 * ^ "PD_1.0" (PDF). Retrieved 2016-04-27. * ^ _A_ _B_ "10 Power Rules", _Universal Serial Bus Power Delivery Specification revision 2.0, version 1.2_, USB
USB
Implementers Forum, 2016-03-25, retrieved 2016-04-09 * ^ Burgess, Rick. " USB 3.0 SuperSpeed update to eliminate need for chargers". TechSpot. * ^ " USB 3.0 Promoter Group Announces Availability of USB
USB
Power Delivery Specification" (PDF). 2012-07-18. Retrieved 2013-01-16. * ^ "Edison’s revenge". The Economist. 2013-10-19. Retrieved 2013-10-23. * ^ " USB Power Delivery — Introduction" (PDF). 2012-07-16. Retrieved 2013-01-06. * ^ " USB 3.1 Specification". Retrieved 2014-11-11. * ^ " USB
USB
Future Specifications Industry Reviews" (PDF). Retrieved 2014-08-10. * ^ "A. Power Profiles", _Universal Serial Bus Power Delivery Specification revision 2.0, version 1.2_, USB
USB
Implementers Forum, 2016-03-25, retrieved 2016-04-09 * ^ " USB
USB
Power Delivery" (PDF). _usb.org_. USB-IF. 20 October 2016.

* ^ "Texas Instruments" (PDF). Retrieved 2016-04-01. * ^ "Cypess". Retrieved 2016-04-01. * ^ " USB-C charging: Universal or bust! We plug in every device we have to chase the dream". Retrieved 30 December 2016. * ^ "Charge All Your Devices Using the Anker PowerPort+ 5 USB-C with USB
USB
Power Delivery". Retrieved 30 December 2016. * ^ Belkin. "Belkin® Launches USB-C Car Charger + Cable With Power Delivery". Retrieved 30 December 2016. * ^ " Belkin USB-C Car Charger + Cable- The World’s First Car Charger with Power Delivery Goes the Distance". Retrieved 30 December 2016. * ^ "Get up to 60 Watts of USB Power Delivery Charging with the iVoler 75W USB
USB
Type C Charger". Retrieved 30 December 2016. * ^ "Innergie PowerGear USB-C 45 charger supports multiple voltages - SlashGear". Retrieved 30 December 2016. * ^ "USB-PD Sniffer". * ^ "ASUS UPD 3.1". * ^ "Toshiba NB200 User Manual" (PDF). UK. 2009-03-01. Retrieved 2014-01-26. * ^ "ThinkPad Ultra Dock". _lenovo.com_. Retrieved 16 September 2016. * ^ " USB
USB
PowerShare Feature". _dell.com_. 2013-06-05. Retrieved 2013-12-04. * ^ " USB
USB
Sleep-and-Charge Ports". _toshiba.com_. Retrieved 2014-12-21. * ^ " USB
USB
Charge Manager". _packardbell.com_. Retrieved 2014-04-25. * ^ Cai Yan (2007-05-31). " China
China
to enforce universal cell phone charger". EE Times. Retrieved 2007-08-25. * ^ 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. * ^ Lam, Crystal; Liu, Harry (22 October 2007). "How to conform to China\'s new mobile phone interface standards". Wireless
Wireless
Net DesignLine. Retrieved 2010-06-22. * ^ "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. Retrieved 2007-11-26.

* ^ _A_ _B_ "Agreement on Mobile phone
Mobile phone
Standard Charger" (Press release). GSM World. * ^ "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. Retrieved 2010-06-22. * ^ "Meeting the challenge of the universal charge standard in mobile phones". Planet Analog. Retrieved 2010-06-22. * ^ "The Wireless
Wireless
Association Announces One Universal Charger Solution to Celebrate Earth Day" (Press release). CTIA. 2009-04-22. Retrieved 2010-06-22. * ^ "ITU" (Press release). 2009-10-22. Retrieved 2010-06-22. * ^ "chargers". EU: EC. 2009-06-29. Retrieved 2010-06-22. * ^ "Europe gets universal cellphone charger in 2010". Wired. 2009-06-13. Retrieved 2010-06-22. * ^ "One size-fits-all mobile phone charger: IEC publishes first globally relevant standard". International Electrotechnical Commission. 2011-02-01. Retrieved 2012-02-20. * ^ "Part 2 - Electrical". MQP Electronics Ltd. Retrieved 2014-12-29. * ^ "Watt to Know About iPhone & iPad Power Adapters Analysis". The Mac Observer. Retrieved 2011-12-12. * ^ "Nook Color charger uses special Micro- USB
USB
connector". barnesandnoble.com. 2011-07-03. * ^ _A_ _B_ "Seagate FreeAgent GoFlex Ultra-portable" (review). CNet. Retrieved 2011-05-22. * ^ Schwarz, Rohde (2012-05-25). " USB
USB
2.0 Mask Testing" (PDF). Retrieved 2012-07-12. * ^ " USB
USB
2.0\'s Real Deal", News & Trends, _PC World_, 2002-02-28 * ^ " NEC
NEC
ready to sample \'world\'s first\' USB 3.0 controller chip". Retrieved 2009-06-15. * ^ "When will USB 3.0 products hit the market?". Retrieved 2009-05-11. * ^ "Mouse stuff you ought to know about", _Urban terror_, 2008-08-09 * ^ _OS dev - Universal Serial Bus_, 2011-02-01 * ^ " USB
USB
in a NutShell—Chapter 2—Hardware". Beyond Logic.org. Retrieved 2007-08-25. * ^ "Technical Specifications of the USB 3.0 SuperSpeed Cables". 100717 usb3.com * ^ _A_ _B_ "Universal Serial Bus 3.0 Specification, Rev 1.0 November 12, 2008" (PDF). 100717 usb3.com * ^ _A_ _B_ " USB
USB
Made Simple, Part 3. Data Flow". _usbmadesimple.co.uk_. 2008. Retrieved 2014-08-17. * ^ _A_ _B_ " USB
USB
in a NutShell, Chapter 3. USB
USB
Protocols". _beyondlogic.org_. 2010-09-17. Retrieved 2014-08-17. * ^ "Part 7, High Speed Transactions: Ping Protocol". _usbmadesimple.co.uk_. 2008. Retrieved 2014-08-16. * ^ " USB
USB
in a Nut Shell". Chapter 4 - Endpoint Types. Retrieved 2014-09-05. * ^ "Debugging Common USB
USB
Issues". Retrieved 2013-06-05. * ^ www.usb.org/developers/docs/devclass_docs/BasicAudioDevice-10.zip * ^ "32-bit Atmel Microcontroller Application Note" (PDF). Atmel Corporation. 2011. Retrieved 13 April 2016. * ^ " FireWire vs. USB
USB
2.0" (PDF). QImaging. Retrieved 2010-07-20. * ^ " FireWire vs. USB
USB
2.0 – Bandwidth Tests". Retrieved 2007-08-25. * ^ " USB
USB
2.0 vs FireWire". Pricenfees. Retrieved 2007-08-25. * ^ Metz, Cade (2003-02-25). "The Great Interface-Off: FireWire Vs. USB
USB
2.0". PC Magazine. Retrieved 2007-08-25. * ^ Heron, Robert. " USB
USB
2.0 Versus FireWire". TechTV. Retrieved 2007-08-25. * ^ " FireWire vs. USB
USB
2.0". USB
USB
Ware. Retrieved 2007-03-19. * ^ Key, Gary (2005-11-15). "Firewire and USB
USB
Performance". Retrieved 2008-02-01. * ^ "802.3, Section 14.3.1.1" (PDF). IEEE. * ^ "Powerbook Explodes After Comcast Plugs In Wrong Cable". Consumerist. 2010-03-08. Retrieved 2010-06-22. * ^ "How Thunderbolt Technology Works: Thunderbolt Technology Community". Thunderbolttechnology.net. Retrieved 2014-01-22. * ^ _One port to rule them all: Thunderbolt 3 and USB Type-C join forces_, retrieved 2015-06-02 * ^ _ Thunderbolt 3 is twice as fast and uses reversible USB-C_, retrieved 2015-06-02 * ^ _ Thunderbolt 3 embraces USB Type-C connector, doubles bandwidth to 40Gbps_, retrieved 2015-06-02 * ^ "Interchip Connectivity: HSIC, UniPro, HSI, C2C, LLI... oh my!". Retrieved 2011-06-24. * ^ " USB
USB
High Speed Inter-Chip Interface". Retrieved 2011-06-24. * ^ "Transitioning from USB
USB
2.0 HSIC to USB 3.0 SSIC". _synopsys.com_. Retrieved 2015-08-07.

FURTHER READING

* 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.

EXTERNAL LINKS

_ Wikimedia Commons has media related to USB
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

.