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| History | |
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The basic USB trident logo; each released version has a specific logo variant[clarification needed]
A group of seven companies began development on USB in 1994: Compaq, DEC, IBM, Intel, Microsoft, NEC and 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. The first silicon for USB was made by Intel in 1995.[3]
The original USB 1.0 specification, which was introduced in January 1996, defined data transfer rates of 1.5 Mbit/s "Low Speed" and 12 Mbit/s "Full Speed".[3] 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 joysticks.[4]
A USB Standard Type A plug, the most common USB plug
The USB 2.0 specification was released in April 2000 and was ratified by the USB Implementers Forum (USB-IF) at the end of 2001. Hewlett-Packard, Intel, Lucent Technologies (now Alcatel-Lucent), NEC and Philips 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.[5] USB 3.0 includes a new, higher speed bus called SuperSpeed in parallel with the USB 2.0 bus.[6] For this reason, the new version is also called SuperSpeed.[7] The first USB 3.0 equipped devices were presented in January 2010.[7][8]
[edit] Tags:Bus,Mbit/s,Disk Drives,Edit,Compaq,Dec,Ibm,Intel,Microsoft,Nec,Joysticks,Hewlett-packard,Lucent Technologies,H, | |
| Prereleases | |
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The USB standard evolved through several versions before its official release in 1995:
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.
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| USB 1.0 | |
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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.
[edit] Tags: | |
| USB 2.0 | |
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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 USB.org:
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. These should not be confused with Micro-B plug and receptacle.
Errata as of December 2000: Released in December 2000.
Pull-up/Pull-down Resistors ECN: Released in May 2002.
Errata as of May 2002: Released in May 2002.
Interface Associations ECN: Released in May 2003.
New standard descriptor was added that allows multiple interfaces to be associated with a single device function.
Rounded Chamfer ECN: Released in October 2003.
A recommended, compatible change to Mini-B plugs that results in longer lasting connectors.
Unicode ECN: Released in February 2005.
This ECN specifies that strings are encoded using UTF-16LE. USB 2.0 did specify that Unicode is to be used but it did not specify the encoding.
Inter-Chip 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 devices to communicate with each other without requiring a separate USB host. In practice, one of the USB devices acts as a host for the other device.
Battery Charging Specification 1.1: Released in March 2007 (Updated 15 Apr 2009).
Adds support for dedicated chargers (power supplies with USB connectors), host chargers (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 device is connected to 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 2.0 specification package only USB 3.0 and USB On-The-Go.)
Micro-USB Cables and Connectors Specification 1.01: Released in April 2007.
Link Power Management Addendum ECN: Released in July 2007.
This adds 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[9]: Released in December 2010.
Several changes and increasing limits including allowing 1.5A on charging ports for unconfigured devices, allowing High Speed communication while having a current up to 1.5A and allowing a maximum current of 5A.
[edit] Tags: | |
| USB 3.0 | |
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The Super-Speed USB Logo
Main article: USB 3.0
USB 3.0 was released in November 2008. The standard specifies a maximum transmission speed of up to 5 Gbit/s (625 MB/s), which is more than 10 times as fast as USB 2.0 (480 Mbit/s, or 60 MB/s), although this speed is typically only achieved using powerful professional grade or developmental equipment. USB 3.0 reduces the time required for data transmission, reduces power consumption, and is backward 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.[10] This move effectively opened the specification to hardware developers for implementation in future products. A new feature is the "SuperSpeed" bus, which provides a fourth transfer mode at 5.0 Gbit/s. The raw throughput is 4 Gbit/s (using 8b/10b encoding), and the specification considers it reasonable to achieve around 3.2 Gbit/s (0.4 GB/s or 400 MB/s), increasing as hardware advances in the future take hold. Two-way communication is also possible. In USB 3.0, full-duplex communications are done when using SuperSpeed (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.
Battery Charging Specification 1.2[9]: Released in December 2010.
Several changes and increasing limits including allowing 1.5A on charging ports for unconfigured devices, allowing High Speed communication while having a current up to 1.5A and allowing a maximum current of 5A.
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| System design | |
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The design architecture of USB is asymmetrical in its topology, consisting of a host, a multitude of downstream USB ports, and multiple peripheral devices connected in a tiered-star topology. Additional USB hubs may be included in the tiers, allowing branching into a tree structure with up to five tier levels. A USB host may implement 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.[11][12]
USB devices are linked in series through hubs. One hub is 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 webcam (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 pipes
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 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. USB devices seldom have this many endpoints.
There are two types of pipes: stream and message pipes depending on the type of data 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).
control transfers: 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. A message pipe is a bi-directional pipe connected to a bi-directional endpoint that is exclusively used for control data flow. An endpoint is built into the USB device by the manufacturer and therefore exists permanently. 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 will be ignored. Otherwise, it will be accepted and the data transaction can start. A bi-directional endpoint, on the other hand, accepts both IN and OUT packets.
Two USB receptacles on the front of a computer
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 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 device drivers 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 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 port or the USB device connected to the port.
High-speed USB 2.0 hubs contain devices called transaction translators that convert between high-speed USB 2.0 buses and full and low speed buses. When a high-speed USB 2.0 hub is plugged into a high-speed USB host or hub, it will operate in high-speed mode. The USB hub will then either use one transaction translator per hub to create a full/low-speed bus that is routed to all full and low speed devices on the hub, or will use 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 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.
[edit] Tags:Pointing Devices,Asymmetrical,Peripheral Devices,Star Topology,Tuple,Polls,Microphone,Keyboard, | |
| Device classes | |
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The functionality of USB devices is defined by class codes, communicated to the USB host to effect the loading of suitable software driver modules for each connected device. This provides for adaptability and device independence of the host to support new devices from different manufacturers.
Device classes include:[13]
Class
Usage
Description
Examples, or exception
00h
Device
Unspecified[14]
Device class is unspecified, interface descriptors are used to determine needed drivers
01h
Interface
Audio
Speaker, microphone, sound card, MIDI
02h
Both
Communications and CDC Control
Modem, Ethernet adapter, Wi-Fi adapter
03h
Interface
Human interface device (HID)
Keyboard, mouse, joystick
05h
Interface
Physical Interface Device (PID)
Force feedback joystick
06h
Interface
Image
Webcam, scanner
07h
Interface
Printer
Laser printer, inkjet printer, CNC machine
08h
Interface
Mass storage
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: communications and CDC control
0Bh
Interface
Smart Card
USB smart card reader
0Dh
Interface
Content security
Fingerprint reader
0Eh
Interface
Video
Webcam
0Fh
Interface
Personal Healthcare
Pulse monitor (watch)
DCh
Both
Diagnostic Device
USB compliance testing device
E0h
Interface
Wireless Controller
Bluetooth adapter, Microsoft RNDIS
EFh
Both
Miscellaneous
ActiveSync device
FEh
Interface
Application-specific
IrDA Bridge, Test & Measurement Class (USBTMC),[15] USB DFU (Direct Firmware update)[16]
FFh
Both
Vendor-specific
Indicates that a device needs vendor specific drivers
[edit] Tags:Speaker,Sound Card,Modem, | |
| USB mass storage | |
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A flash drive, a typical USB mass-storage device
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, but has been extended to support a wide variety of devices, particularly flash drives, 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 SD card with a USB adapter is particularly advantageous for maintaining the integrity and non-corruptible, pristine state of the booting medium.
Though most post-2005 computers are capable of booting from USB mass storage devices, USB is not intended to be a primary bus for a computer's internal storage: buses such as Parallel ATA (PATA or IDE), Serial ATA (SATA), or 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. Originally conceived and still used today for optical storage devices (CD-RW drives, DVD drives and so on), several manufacturers offer external portable USB hard disk drives, 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 30 MB/s for USB 2.0 and potentially 400 MB/s or more[17] 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 eSATA, ExpressCard (now at version 2.0), and FireWire (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.[18][19]
[edit] Tags:Serial,Computers, | |
| Human interface devices (HIDs) | |
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Main article: USB human interface device class
Joysticks, keypads, tablets and other human-interface devices are also progressively migrating from MIDI, and PC game port connectors to USB.[citation needed]
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. Such adaptors contain no logic circuitry: 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 microcontroller to perform bidirectional translation of data between the two standards.[citation needed]
[edit] Tags:Game Port, | |
| Physical appearance | |
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Pinouts of Standard, Mini, and Micro USB plugs. The USB logo is on the bottom of the two micro-USB plugs (as they are shown in this figure) but on the top of the other plugs[20]
Micro-B USB 3.0 compatible (cable/male end)
USB 2.0 connector on the side of the specification standard micro USB 3.0 connector are aligned pin-minute increase in the standard.
No.1: power (VBUS)
No.2: USB 2.0 differential pair (D−)
No.3: USB 2.0 differential pair (D+)
No.4: USB OTG ID for identifying lines
No.5: GND
No.6: USB 3.0 signal transmission line (−)
No.7: USB 3.0 signal transmission line (+)
No.8: GND
No.9: USB 3.0 signal receiving line (−)
No.10: USB 3.0 signal receiving line (+)
USB 1.x/2.0 standard pinout
Pin
Name
Cable color
Description
1
VBUS
Red
+5 V
2
D−
White
Data −
3
D+
Green
Data +
4
GND
Black
Ground
USB 1.x/2.0 Mini/Micro pinout
Pin
Name
Cable color
Description
1
VBUS
Red
+5 V
2
D−
White
Data −
3
D+
Green
Data +
4
ID
None
Permits distinction of host connection from slave connection
* host: connected to Signal ground
* slave: not connected
5
GND
Black
Signal ground
[edit] Tags: | |
| Connector properties | |
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Standard type A plug and receptacle
The 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.[21] 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.
[edit] Tags: | |
| Usability and "upside down" connectors | |
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USB extension cord
By design, it is difficult to attach a USB connector incorrectly. Connectors cannot be plugged in upside down and it is clear from the physical act 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.[21]
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.[citation needed]
The standard connectors were deliberately intended to enforce the directed topology 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) gender changers make little sense with USB and are almost never used.[citation needed]
[edit] Tags: | |
| Durability | |
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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.
The newer Micro-USB receptacles are designed for up to 10,000 cycles of insertion and removal between the receptacle and plug, compared to 1,500 for the standard USB and 5,000 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 c Tags: | |
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