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This article is about the computer bus to connect peripherals. For other uses of USB, see. The basic USB trident logo; each released variant has a specific logo variant A group of seven companies began development on USB in 1994:,. 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. The first silicon for USB was made by Intel in 1995.The original USB 1.0 specification, which was introduced in January 1996, defined data transfer rates of 1.5 /s “Low Speed” and 12 Mbit/s “Full Speed”. The first widely used version of 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.
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A USB Standard Type A plug, the most commonThe USB 2.0 specification was released in April 2000 and was standardized by the (USB-IF) at the end of 2001., Intel, (now Alcatel-Lucent), NEC and jointly led the initiative to develop a higher data transfer rate, with the resulting specification achieving 480 Mbit/s, a fortyfold increase over the original 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), to decrease power consumption, to increase power output, and to be backwards-compatible with USB 2.0. USB 3.0 includes a new, higher speed bus called SuperSpeed in parallel with the 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. Version history.
In-built USB female sockets on a Sony Vaio E series laptop Prereleases. USB 0.7: Released in November 1994. USB 0.8: Released in December 1994. USB 0.9: Released in April 1995. USB 0.99: Released in August 1995.
USB 1.0 Release Candidate: Released in November 1995. USB 1.0. USB 1.0: Released in January 1996.Specified data rates of 1.5 Mbit/s ( Low-Bandwidth) and 12 Mbit/s ( Full-Bandwidth). Does not allow for extension cables or pass-through monitors (due to timing and power limitations). Few such devices actually made it to market.
USB 1.1: Released in August 1998.Fixed problems identified in 1.0, mostly relating to hubs. Earliest revision to be widely adopted. USB 2.0. The Hi-Speed USB Logo.
USB 2.0: Released in April 2000.Added higher maximum bandwidth of 480 Mbit/s (60 MB/s) (now called “Hi-Speed”). Further modifications to the USB specification have been done via Engineering Change Notices (ECN). The most important of these ECNs are included into the USB 2.0 specification package available from:. Mini-A and Mini-B Connector ECN: Released in October 2000.Specifications for Mini-A and B plug and receptacle. Also receptacle that accepts both plugs for On-The-Go. Main article:USB 3.0 has transmission speeds of up to 5 Gbit/s, which is 10 times faster than USB2.0 (480 Mbit/s). USB 3.0 significantly reduces the time required for data transmission, reduces power consumption, and is downward compatible with USB 2.0.
The USB 3.0 Promoter Group announced on 17 November 2008 that the specification of version 3.0 had been completed and had made the transition to the USB Implementers Forum (USB-IF), the managing body of USB specifications. This move effectively opened the specification to hardware developers for implementation in future products. System designA USB system has an design, consisting of a, a multitude of downstream USB ports, and multiple connected in a tiered. Additional may be included in the tiers, allowing branching into a tree structure with up to five tier levels. A USB host may have multiple host controllers and each host controller may provide one or more USB ports. Up to 127 devices, including hub devices if present, may be connected to a single host controller.USB devices are linked in series through hubs. There always exists one hub known as the root hub, which is built into the host controller.A physical 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 (video device function) with a built-in microphone (audio device function). Such a device is called a compound device in which each logical device is assigned a distinctive address by the host and all logical devices are connected to a built-in hub to which the physical USB wire is connected. A host assigns one and only one device address to a function. USB endpoints actually reside on the connected device: the channels to the host are referred to as pipesUSB 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. Because pipes correspond 1-to-1 to endpoints, the terms are sometimes used interchangeably.
A USB device can have up to 32 endpoints: 16 into the host controller and 16 out of the host controller. The USB standard reserves one endpoint of each type, leaving a theoretical maximum of 30 for normal use. Two USB receptacles on the front of a computerEndpoints 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 which 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 device is first connected to a USB host, the USB device enumeration process is started.
The enumeration starts by sending a reset signal to the USB device. The data rate of the USB device is determined during the reset signaling. After reset, the 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 needed for communicating with the device are loaded and the device is set to a configured state. If the USB host is restarted, the enumeration process is repeated for all connected devices.The host controller directs traffic flow to devices, so no USB device can transfer any data on the bus without an explicit request from the host controller.
In USB 2.0, the host controller the bus for traffic, usually in a fashion. The slowest device connected to a controller sets the bandwidth of the interface. For SuperSpeed USB (defined since USB 3.0), connected devices can request service from host. Because there are two separate controllers in each USB 3.0 host, USB 3.0 devices will transmit and receive at USB 3.0 data rates regardless of USB 2.0 or earlier devices connected to that host. Operating data rates for them will be set in the legacy manner.
Device classesUSB defines class codes used to identify a device’s functionality and to load a device driver based on that functionality. A, a typical USB mass-storage deviceUSB implements connections to storage devices using a set of standards called the USB mass storage device class (referred to as MSC or UMS). This was initially intended for traditional magnetic and optical drives, but has been extended to support a wide variety of devices, particularly. This generality is because 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 with a USB adapter is particularly advantageous for maintaining the integrity and non-corruptible, pristine state of the booting medium.Though most newer computers are capable of booting off USB mass storage devices, USB is not intended to be a primary bus for a computer’s internal storage: buses such as (PATA or IDE), (SATA), or 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 , making it useful for mobile peripherals, including drives of various kinds. Originally conceived and still used today for optical storage devices ( drives, drives and so on), several manufacturers offer external portable USB, or empty enclosures for disk drives, which offer performance comparable to internal drives, limited by the current number and type of attached USB devices and by the upper limit of the USB interface (in practice about 40 MB/s for USB 2.0 and potentially 400 MB/s or more for USB 3.0). These external drives have typically included a “translating device” that bridges between a drive’s interface to a USB interface port. Functionally, the drive appears to the user much like an internal drive. Other competing standards for external drive connectivity include, (now at version 2.0), and (IEEE 1394).Another use for 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. Human interface devices (HIDs). Main article:Mice and keyboards usually have USB connectors.
These can be used with older computers that have with the aid of a small USB-to-PS/2 adapter. Such adaptors contain no: the hardware in the USB keyboard or mouse is designed to detect whether it is connected to a USB or PS/2 port, and communicate using the appropriate protocol. Converters also exist to allow PS/2 keyboards and mice (usually one of each) to be connected to a USB port. These devices present two HID endpoints to the system and use a to perform bidirectional translation of data between the two standards.Joysticks, keypads, tablets and other human-interface devices are also progressively migrating from, and PC connectors to USB. Physical appearance. Standard type A plug and receptacleThe connectors specified by the USB committee were designed to support a number of USB’s underlying goals, and to reflect lessons learned from the menagerie of connectors which have been used in the computer industry.
The connector mounted on the host or device is called the receptacle, and the connector attached to the cable is called the plug. In the case of an extension cable, the connector on one end is a receptacle. The official USB specification documents periodically define the term male to represent the plug, and female to represent the receptacle.
Usability and “upside down” connectors. USB extension cordBy design, it is difficult to attach a USB connector incorrectly.
Connectors cannot be plugged in upside down and it is clear from sensation of making a connection when the plug and receptacle are correctly mated. The USB specification states that the required USB Icon is to be “embossed” on the “topside” of the USB plug, which “provides easy user recognition and facilitates alignment during the mating process”.
The specification also shows that the “recommended” (optional) “Manufacturer’s logo” (“engraved” on the diagram but not specified in the text) is on the opposite side of the USB Icon. The specification further states “the 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.
Only moderate insertion/removal force is needed. USB cables and small 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). The force needed to make or break a connection is modest, allowing connections to be made in awkward circumstances (i.e., behind a floor-mounted chassis, or from below) or by those with motor disabilities. This has the disadvantage of easily and unintentionally breaking connections that one has intended to be permanent in case of cable accident (e.g., tripping, or inadvertent tugging). Conversely, this prevents damage to the receptacle or device into which it is plugged allowing the cable to come free before pulling the device off a desk or shelf in the same accident above. The standard connectors were deliberately intended to enforce the directed of a USB network: type A connectors on host devices that supply power and type B connectors on target devices that receive power.
This prevents users from accidentally connecting two USB power supplies to each other, which could lead to dangerously high currents, circuit failures, or even fire. USB does not support cyclical networks and the standard connectors from incompatible USB devices are themselves incompatible. Unlike other communications systems (e.g. Network cabling) make little sense with USB and are almost never used, although cables with 2 standard type A plugs are commonly found in inexpensive retail outlets. Durability. The standard connectors were designed to be robust. Many previous connector designs were fragile, specifying embedded component pins or other delicate parts which proved vulnerable to bending or breakage, even with the application of modest force.
The electrical contacts in a USB connector are protected by an adjacent plastic tongue, and the entire connecting assembly is usually protected by an enclosing metal sheath. The connector 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 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, a common practice in the design of connectors in the. The newer receptacles are designed for up to 10,000 cycles of insertion and removal between the receptacle and plug, compared to 1500 for the standard USB and 5000 for the Mini-USB receptacle.
This is accomplished by adding a locking device and by moving the leaf-spring connector 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 instead of the more expensive micro-USB device. Compatibility.
(eSATA/USB) combo port is compatible with USB devices. The USB standard specifies relatively loose tolerances for compliant USB connectors to minimize physical incompatibilities in connectors from different vendors. To address a weakness present in some other connector standards, the 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 which does. Two-way communication is also possible.
In USB 3.0, full-duplex communications are done when using (USB 3.0) transfer. In previous USB versions (i.e., 1.x or 2.0), all communication is half-duplex and directionally controlled by the host.In general, cables have only plugs (very few have a receptacle on one end, although extension cables with a standard A plug and jack are sold), and hosts and devices have only receptacles. Hosts almost universally have type-A receptacles, and devices one or another type-B variety. Type-A plugs mate only with type-A receptacles, and type-B with type-B; they are deliberately physically incompatible. However, an extension to USB standard specification called allows a single port to act as either a host or a device—chosen by which end of the cable plugs into the receptacle on the 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 in which the 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.
USB 3.0 receptacles are electrically compatible with USB Standard 2.0 device plugs if they physically match. USB 3.0 type-A plugs and receptacles are completely backward compatible, and USB 3.0 type-B receptacles will accept USB 2.0 and earlier plugs. However, USB 3.0 type-B plugs will not fit into USB 2.0 and earlier receptacles. (eSATA/USB) port is also compatible with USB 2.0 devices. Connector types.
Types of USB connectors left to right (ruler in centimeters) (vertical reading):. Micro-B plug. proprietary (not USB). Mini-B plug (5-pin). Standard-A receptacle. Standard-A plug.
Standard-B plugThere are several types of USB connectors, including some that have been added while the specification progressed. The original USB specification detailed Standard-A and Standard-B plugs and receptacles. The first engineering change notice to the USB 2.0 specification added Mini-B plugs and receptacles.The data connectors in the Standard-A plug are actually recessed in the plug as compared to the outside power connectors. This permits the power to connect first which prevents data errors by allowing the device to power up first and then transfer the data. Some devices will operate in different modes depending on whether the data connection is made. This difference in connection can be exploited by inserting the connector only partially.
For example, some battery-powered MP3 players switch into file transfer mode and cannot play MP3 files while a USB plug is fully inserted, but can be operated in MP3 playback mode using USB power by inserting the plug only part way so that the power slots make contact while the data slots do not. This enables those devices to be operated in MP3 playback mode while getting power from the cable.To reliably enable a charge-only feature, modern 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 device to be charged and/or operated from a standard USB cable. USB standard connectors. Pin configuration of the USB connectors Standard A/B, viewed looking into face/end of plugThe USB 2.0 Standard-A type of USB plug is a flattened rectangle which inserts into a “downstream-port” receptacle on the USB host, or a hub, and carries both power and data. This plug is frequently seen on cables that are permanently attached to a device, such as one connecting a keyboard or mouse to the computer via usb connection.USB connections eventually wear out as the connection loosens through repeated plugging and unplugging. The lifetime of a USB-A male connector is approximately 1,500 connect/disconnect cycles.A Standard-B plug—which has a square shape with bevelled exterior corners—typically plugs into an “upstream receptacle” on a device that uses a removable cable, e.g. A Type B plug delivers power in addition to carrying data.
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 an. Mini and Micro connectors. USB Mini A (left) and USB Mini B (right) plugsVarious connectors have been used for smaller devices such as PDAs, mobile phones or digital cameras. These include the now-deprecated (but standardized) Mini-A and the currently standard Mini-B, Micro-A, and Micro-B connectors. The Mini-A and Mini-B plugs are approximately 3 by 7.The micro-USB plugs have a similar but approximately half the thickness, enabling their integration into thinner portable devices. The micro-A connector is 6.85 by 1.8 with a maximum overmold size of 11.7 by 8.5 mm.
The micro-B connector is 6.85 by 1.8 mm with a maximum overmold size of 10.6 by 8.5 mm.The Micro-USB connector was announced by the on 4 January 2007. The Mini-A connector and the Mini-AB receptacle connector were deprecated on 23 May 2007. As of February 2009, many currently available devices and cables still use Mini plugs, but the newer Micro connectors are being widely adopted and as of December 2010, the Micro connectors are the most widely used.
The thinner micro connectors are intended to replace the Mini plugs in new devices including. The Micro plug design is rated for at least 10,000 connect-disconnect cycles which is significantly more than the Mini plug design. The Universal Serial Bus Micro-USB Cables and Connectors Specification details the mechanical characteristics of Micro-A, Micro-AB, and Micro-B plugs and receptacles, along with a Standard-A receptacle to Micro-A plug adapter.The cellular phone carrier group, (OMTP) in 2007 have endorsed Micro-USB as the standard connector for data and power on mobile devices.
These include various types of battery chargers, allowing Micro-USB to be the single external cable link needed by some devices.As of 30 January 2009 Micro-USB has been accepted and is being used by almost all cell phone manufacturers as the standard charging port (including HTC, Motorola, Nokia, LG, Hewlett-Packard, Samsung, Sony Ericsson, Research In Motion) in most of the world. On 29 June 2009, following a request from the and in close co-operation with the Commission services, major producers of mobile phones have agreed in a (“MoU”) to harmonise chargers for data-enabled mobile phones sold in the European Union. Industry commits to provide charger compatibility on the basis of the Micro-USB connector. Consumers will be able to purchase mobile phones without a charger, thus logically reducing their cost. This section does not any.
Please help improve this section by adding citations to. Unsourced material may be. (June 2011). Microsoft’s original uses standard USB 1.1 signalling in its controllers and memory cards, but uses proprietary connectors and ports.
The (pre Xbox 360 S) has two Memory Unit ports which are USB compliant with proprietary connectors. uses standard USB signalling, but via a proprietary connection format.
uses USB signalling and HID device class on its using connectors. Nokia’s discontinued Pop-Port connectorincluded a USB connection as part of the connector on some older mobile phone models. used a proprietary connector called from 2005 to 2009. The second, third, and fourth generation uses a to carry USB, audio, or power signals. added a fifth power pin within USB-A plugs for higher power and faster charging, used for the iriver U10 series. A mini-USB version contains a matching extra power pin for the cradle. Apple has shipped non-standard USB extension cables with some of their computers, for use with the included Apple USB keyboards.
The extension cable’s socket is keyed with a small protrusion to prevent the insertion of a standard USB plug, while the Apple USB keyboard’s plug has a matching indentation. The indentation on the keyboard’s plug does not interfere with insertion into a standard USB socket. Despite the keying, it is still possible to insert standard USB plugs into the extension cord. The protrusion can also be shaved off with an appropriate blade, or crushed with. A USB twisted pair, where the “Data +” and “Data -” conductors are twisted together in a double. The wires are enclosed in a further layer of shielding.
Conductor configurationThe data cables for USB 1.x and USB 2.x use a to reduce. USB 3.0 cables are larger in diameter because there are twice as many wires than USB 2.x. This is to support the new SuperSpeed data transmission. Maximum cable lengthFor USB 2.0 or earlier, the maximum length of a standard cable is 5 metres (16.4 ft). The primary reason for this limit is the maximum allowed round-trip delay of about 1.5 μs. If USB host commands are unanswered by the 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 2.0 specification requires cable delay to be less than 5.2 ns per meter (192,000 km/s, which is close to the maximum achievable transmission speed for standard copper cable). This allows for a five meter cable.
The USB 3.0 standard does not directly specify a maximum cable length, requiring only that all cables meet an electrical specification. For copper wire cabling, some calculations have suggested a maximum length of perhaps 3 m. PowerThe USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines.
For USB 2.0, the voltage supplied by low-powered hub ports is 4.4–5.25 V.A unit load is defined as 100 mA in USB 2.0, and was raised to 150 mA in USB 3.0. A maximum of 5 unit loads (500 mA) can be drawn from a port in USB 2.0, which was raised to 6 (900 mA) in USB 3.0. There are two types of devices: low-power and high-power.
Low-power devices draw at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0, and 4 V in USB 3.0. High-power devices draw the maximum number of unit loads supported by the standard.
All devices default as low-power but the device’s software may request high-power as long as the power is available on the providing bus.Some devices like high-speed external disk drives may require more than 500 mA of current and therefore cannot be powered from one USB 2.0 port. Such devices usually come with Y-shaped cable that has two USB connectors to be inserted into a computer. With such a cable a device can draw power from two USB ports simultaneously.A bus-powered hub is initialized at 1 unit load and transitions to maximum unit loads after hub configuration is obtained.
Any device connected to the hub will draw 1 unit load regardless of the current draw of devices connected to other ports of the hub (i.e. One device connected on a four-port hub will only draw 1 unit load despite the fact that all unit loads are being supplied to the hub).A self-powered hub will supply maximum supported unit loads to any device connected to it. An externally-powered hub (battery or DC converter) may supply maximum unit loads to ports. In addition, the V BUS will supply 1 unit load upstream for communication if parts of the Hub are powered down.In Battery Charging Specification, new powering modes are added to the USB specification.
A host or hub Charging Downstream Port can supply a maximum of 1.5 A when communicating at low-bandwidth or full-bandwidth, a maximum of 900 mA when communicating at high-bandwidth, and as much current as the connector will safely handle when no communication is taking place; USB 2.0 standard-A connectors are rated at 1.5 A by default. A Dedicated Charging Port can supply a maximum of 1.8 A of current at 5.25 V.
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A portable device can draw up to 1.8 A from a Dedicated Charging Port. The Dedicated Charging Port the D+ and D- pins with a resistance of at most 200 Ω. The short disables data transfer, but allows devices to detect the Dedicated Charging Port and allows very simple, high current chargers to be manufactured. The increased current (faster, 9 W charging) will occur once both the host/hub and devices support the new charging specification. Sleep and ChargeSleep-and-charge 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 ports are powered down. This prevents phones and other devices from being able to charge unless the computer is powered on. Sleep-and-charge USB ports remain powered even when the computer is off. On laptops, charging devices from the USB port when it is not being powered from AC will drain the laptop battery faster.
Desktop machines need to remain plugged into AC power for Sleep-and-charge to work. Mobile device charger standards. The Micro-USB interface is commonly found on chargers forAs of 14 June 2007, all new applying for a license in are required to use the USB port as a power port.
This was the first standard to use the convention of shorting D+ and D.In September 2007, the group (a forum of mobile network operators and manufacturers such as, and ) announced that its members had agreed on micro-USB as the future common connector for mobile devices.On 17 February 2009, the (GSMA) announced that they had agreed on a standard charger for mobile phones. The standard connector to be adopted by 17 manufacturers including Nokia, Motorola and Samsung is to be the micro-USB connector (several media reports erroneously reported this as the mini-USB). The new chargers will be much more efficient than existing chargers. Having a standard charger for all phones means that manufacturers will no longer have to supply a charger with every new phone.
USB novelty deviceSome USB devices require more power than is permitted by the specifications for a single port. This is common for external hard and, and generally for devices with. Such devices can use an, which is allowed by the standard, or use a dual-input 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 device. Some external hubs may, in practice, supply more power to USB devices than required by the specification but a standard-compliant device may not depend on this.Some non-standard USB devices use the 5 V power supply without participating in a proper USB network which negotiates power draws with the host interface. These are usually referred to as. The typical example is a USB-powered keyboard light; fans, mug coolers and heaters, battery chargers, miniature, and even miniature are available. In most cases, these items contain no digital circuitry, and thus are not Standard compliant USB devices at all.
This can theoretically cause problems with some computers, such as drawing too much current and damaging circuitry; prior to the Battery Charging Specification, the USB specification required that devices connect in a low-power mode (100 mA maximum) and communicate their current requirements to the host, which would then permit the device to switch into high-power mode.In addition to limiting the total average power used by the device, the USB specification limits the (i.e., that used to charge decoupling and ) when the device is first connected. Otherwise, connecting a device could cause problems with the host’s internal power. Also, USB devices are required to automatically enter ultra low-power suspend mode when the USB host is suspended. Nevertheless, many USB host interfaces do not cut off the power supply to USB devices when they are suspended since resuming from the suspended state would become a lot more complicated if they did.There are also devices at the host end that do not support negotiation, such as battery packs that can power USB-powered devices; some provide power, while others pass through the data lines to a host PC. USB power adapters convert utility power and/or another power source (e.g., a car’s electrical system) to run attached devices.
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Some of these devices can supply up to 1 A of current. Without negotiation, the powered USB device is unable to inquire if it is allowed to draw 100 mA, 500 mA, or 1 A. Powered USB. Main article:Powered USB uses standard USB signaling with the addition of extra power lines.
It uses four additional pins to supply up to 6 A at either 5 V, 12 V, or 24 V (depending on keying) to peripheral devices. The wires and contacts on the USB portion have been upgraded to support higher current on the 5 V line, as well.
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This is commonly used in systems and provides enough power to operate stationary scanners, printers, pads, signature capture devices, etc. This modification of the USB interface is proprietary and was developed by,. It is essentially two connectors stacked such that the bottom connector accepts a standard USB plug and the top connector takes a power connector.
SignalingUSB supports the following: The terms speed and bandwidth are used interchangeably. “high-” is alternatively written as “hi-“. A low-speed rate of 1.5 Mbit/s (183 kB/s) is defined by USB 1.0. It is very similar to full-bandwidth operation except each bit takes 8 times as long to transmit. It is intended primarily to save cost in low-bandwidth (HID) such as keyboards, mice, and joysticks.
The full-speed rate of 12 (1.43 MB/s) is the basic USB data rate defined by USB 1.1. All USB hubs support full-bandwidth. A high-speed (USB 2.0) rate of 480 Mbit/s (57 MB/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 2.0 and USB 1.x. A SuperSpeed (USB 3.0) rate of 4.8 Gbit/s (572 MB/s). The written USB 3.0 specification was released by Intel and partners in August 2008.
The first USB 3 controller chips were sampled by May 2009 and products using the 3.0 specification arrived beginning in January 2010. USB 3.0 connectors are generally backwards compatible, but include new wiring and full duplex operation.USB signals are transmitted on a data cable with 90 ±15%, labeled D+ and D−. Prior to USB 3.0, these collectively use to reduce the effects of electromagnetic on longer lines. Transmitted signal levels are 0.0–0.3 for low and 2.8–3.6 for high in full-bandwidth and low-bandwidth modes, and −10–10 mV for low and 360–440 mV for high in hi-bandwidth mode. In FS mode, the cable wires are not terminated, but the HS mode has of 45 Ω to ground, or 90 Ω differential to match the data cable impedance, reducing interference due to signal.
USB 3.0 introduces two additional pairs of shielded twisted wire and new, mostly interoperable contacts in USB 3.0 cables, for them. They permit the higher data rate, and full duplex operation.A 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 which permitted erroneous connections (and potential damage to the circuitry). USB interconnections are not as fool-proof or as simple as originally intended.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 documentation), and indicates a reset or disconnected connection.A USB device pulls one of the data lines high with a 1.5 kΩ resistor. This overpowers one of the pull-down resistors in the host and leaves the data lines in an idle state called “J”. For USB 1.x, the choice of data line indicates a device’s bandwidth support; full-bandwidth devices pull D+ high, while low-bandwidth devices pull D− high.USB data is transmitted by toggling the data lines between the J state and the opposite K state.
USB encodes data using the convention; a 0 bit is transmitted by toggling the data lines from J to K or vice-versa, while a 1 bit is transmitted by leaving the data lines as-is. To ensure a minimum density of signal transitions remains in the, USB uses; an extra 0 bit is inserted into the data stream after any appearance of six consecutive 1 bits. Seven consecutive received 1 bits is always an error. USB 3.0 has introduced additional data transmission encodings.A USB packet begins with an 8-bit synchronization sequence ‘00000001’. 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.A USB packet’s end, called EOP (end-of-packet), 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 ‘1’s. This bit should be ignored by receiver.A USB bus is reset using a prolonged (10 to 20 milliseconds) SE0 signal.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 HS capable first connects as an FS device (D+ pulled high), but upon receiving a 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 will operate at high bandwidth. The device has to receive at least 3 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 2.0 and USB 1.x, such bandwidth negotiation is not required.Clock tolerance is 480.00 Mbit/s ±500, 12.000 Mbit/s ±2500 ppm, 1.50 Mbit/s ±15000 ppm.Though high bandwidth devices are commonly referred to as “USB 2.0” and advertised as “up to 480 Mbit/s”, not all USB 2.0 devices are high bandwidth. The certifies devices and provides licenses to use special marketing logos for either “basic bandwidth” (low and full) or high bandwidth after passing a compliance test and paying a licensing fee. All devices are tested according to the latest specification, so recently compliant low bandwidth devices are also 2.0 devices.USB 3 uses tinned copper stranded AWG-28 cables with 90±7 Ω impedance for its high-speed differential pairs and and sent with a voltage of 1 V nominal with a 100 mV receiver threshold; the receiver uses equalization.
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. Transfer ratesThe theoretical maximum data rate in USB 2.0 is 480 Mbit/s (60 MB/s) per controller and is shared amongst all attached devices. Some chipset manufacturers overcome this bottleneck by providing multiple USB 2.0 controllers within the.Typical hi-speed USB hard drives can be written to at rates around 25–30 MB/s, and read from at rates of 30–42 MB/s, according to routine testing done. This is 70% of the total bandwidth available.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 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 spec.For 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 of the transmission. CommunicationUSB communication takes the form of. 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. 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 will never need bit-stuffing, even when combined with the final 1 bit in the sync byte.