Universal Serial Bus ( USB )
In information technology, Universal Serial Bus (USB) is a serial bus standard to connect devices to a host computer. USB was designed to allow many peripherals to be connected using a single standardized interface socket and to improve plug and play capabilities by allowing hot swapping; that is, by allowing devices to be connected and disconnected without rebooting the computer or turning off the device. Other convenient features include providing power to low-consumption devices, eliminating the need for an external power supply; and allowing many devices to be used without requiring manufacturer-specific device drivers to be installed.
USB is intended to replace many varieties of serial and parallel ports. USB can connect computer peripherals such as mice, keyboards, PDAs, gamepads and joysticks, scanners, digital cameras, printers, personal media players, flash drives, and external hard drives. For many of those devices, USB has become the standard connection method. USB was designed for personal computers, but it has become commonplace on other devices such as PDAs and video game consoles, and as a power cord between a device and an AC adapter plugged into a wall plug for charging. As of 2008[update], there are about 2 billion USB devices sold per year, and about 6 billion total sold to date.[1]
The design of USB is standardized by the USB Implementers Forum (USB-IF), an industry standards body incorporating leading companies from the computer and electronics industries. Notable members have included Agere (now merged with LSI Corporation), Apple Inc., Hewlett-Packard, Intel, Microsoft and NEC.
History
The USB 1.0 specification was introduced in 1994. USB was created by the core group of companies that consisted of Intel, Compaq, Microsoft, Digital, IBM, and Northern Telecom. Intel produced the UHCI host controller and open software stack; Microsoft produced a USB software stack for Windows and co-authored the OHCI host controller specification with National Semiconductor and Compaq; Philips produced early USB-Audio; and TI produced the most widely used hub chips. USB was intended to replace the multitude of connectors at the back of PCs, as well as to simplify software configuration of communication devices.
The USB 2.0 specification was released in April 2000 and was standardized by the USB-IF at the end of 2001. Hewlett-Packard, Intel, Lucent (now LSI Corporation since its merger with Lucent spinoff Agere Systems (Lucent has been merged with Alcatel, and became Alcatel-Lucent)), Microsoft, NEC, and Philips jointly led the initiative to develop a higher data transfer rate, 480 Mbit/s, than the 1.0 specification of 12 Mbit/s.
The USB 3.0 specification was released on November 17, 2008 by the USB 3.0 Promoter Group. It has a transfer rate of up to 10 times faster than the USB 2.0 version and has been dubbed the SuperSpeed USB.
Equipment conforming with any version of the standard will also work with devices designed to any previous specification (a property known as backward compatibility).
Device classes
USB defines class codes used to identify a device’s functionality and to load a device driver based on that functionality. This enables a device driver writer to support devices from different manufacturers that comply with a given class code.
Device classes include
Note class 0: Use class information in the Interface Descriptors. This base class is defined to be used in Device Descriptors to indicate that class information should be determined from the Interface Descriptors in the device.
Types of USB connector
There 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 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
USB-A
The Standard-A type of USB connector takes on the appearance of a flattened rectangle that plugs into downstream-port sockets on the USB host or a hub and receives power. This kind of connector is most frequently seen on cables that are permanently attached to a device, such as one on a cable that connects a keyboard or mouse to the computer.
USB-B
Standard-B connectors—which have a square shape with beveled exterior corners—typically plug into upstream sockets on devices that use a removable cable, e.g. between a hub and a printer. Type B plugs deliver power and are therefore analogous to a power socket. This two-connector scheme prevents a user from accidentally creating a loop.
Mini and micro
Various connectors have been used for smaller devices such as PDAs, mobile phones or digital cameras. These include the now-deprecated[12] (but standardized) Mini-A and the current standard Mini-B, Micro-A, and Micro-B connectors. The Mini-A and Mini-B plugs are approximately 3 by 7 mm, while the Micro plugs have a similar width but approximately half the thickness, enabling their integration into thinner portable devices.
The Micro-USB connector was announced by the USB-IF on January 4, 2007 and the Mini-USB connectors were withdrawn[citation needed]. As of February 2009[update], most available devices and cables still use Mini plugs, but the newer Micro connectors are becoming more widely adopted. The thinner Micro connectors are intended to replace the Mini plugs in new devices including smartphones and personal digital assistants. The Micro plug design is rated for 10,000 connect-disconnect cycles. The Universal Serial Bus Micro-USB Cables and Connectors Specification details the mechanical characteristics of Micro-A plugs, Micro-AB receptacles, and Micro-B plugs and receptacles, along with a Standard-A receptacle to Micro-A plug adapter. The carrier-led Open Mobile Terminal Platform (OMTP) group have recently endorsed micro-USB as the standard connector for data and power on mobile devices.[14] These include various types of battery chargers, allowing Micro-USB to be the single external cable link needed by some devices.
USB OTG Sockets: Mini-AB, Micro-AB
Except for special standard-to-Mini-A and standard-to-Micro-A adapters, USB cables always have an A-connector and a B-connector, on opposite ends. A-connectors can always connect to A-sockets; B-connectors can always connect B-sockets. These sockets all come in standard, mini, and micro versions.
For USB On-The-Go (or 'OTG') support for another socket type is defined: the AB, in both mini and micro versions. It can accept both A and B connector, through careful mechanical design. OTG software detects the difference by use of the ID pin, which is grounded in A-connectors and is otherwise floating. When an A-connector is connected to an AB socket, the socket supplies VBUS power to the cable and starts in the host role. When a B-connector is used, the socket consumes VBUS power and starts in the peripheral or device role. OTG allows those two roles to be switched by software, as needed for the task at hand.
Version history
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-Speed) and 12 Mbit/s (Full-Speed). 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 September 1998.
Fixed problems identified in 1.0, mostly relating to hubs. Earliest revision to be widely adopted.
USB 2.0
Hi-Speed USB LogoUSB 2.0: Released in April 2000.
Added higher maximum speed of 480 Mbit/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-B Connector ECN: Released in October 2000.
Specifications for Mini-B plug and receptacle. 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 1.0: Released in March 2007.
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 1.8A. (Note that this document is not distributed with USB 2.0 specification package.)
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.
High-Speed Inter-Chip USB Electrical Specification Revision 1.0: Released in September 2007.
USB 3.0
On September 18, 2007, Pat Gelsinger demonstrated USB 3.0 at the Intel Developer Forum. The USB 3.0 Promoter Group announced on November 17, 2008, that version 1.0 of the specification has been completed and is transitioned to the USB Implementers Forum (USB-IF), the managing body of USB specifications.[34] This move effectively opens the spec to hardware developers for implementation in future products.
Availability
Consumer products are expected to become available in 2010. Commercial controllers are expected to enter into volume production no later than the first quarter of 2010.[38] NEC is aiming to produce its first USB controller in June 2009, initially priced at USD 15.00
Windows 7 drivers are under development but no public releases have been made available as of May 2009. The Linux Kernel supports USB 3.0 as of version 2.6.30.
Reference: Wikipedia
In information technology, Universal Serial Bus (USB) is a serial bus standard to connect devices to a host computer. USB was designed to allow many peripherals to be connected using a single standardized interface socket and to improve plug and play capabilities by allowing hot swapping; that is, by allowing devices to be connected and disconnected without rebooting the computer or turning off the device. Other convenient features include providing power to low-consumption devices, eliminating the need for an external power supply; and allowing many devices to be used without requiring manufacturer-specific device drivers to be installed.
USB is intended to replace many varieties of serial and parallel ports. USB can connect computer peripherals such as mice, keyboards, PDAs, gamepads and joysticks, scanners, digital cameras, printers, personal media players, flash drives, and external hard drives. For many of those devices, USB has become the standard connection method. USB was designed for personal computers, but it has become commonplace on other devices such as PDAs and video game consoles, and as a power cord between a device and an AC adapter plugged into a wall plug for charging. As of 2008[update], there are about 2 billion USB devices sold per year, and about 6 billion total sold to date.[1]
The design of USB is standardized by the USB Implementers Forum (USB-IF), an industry standards body incorporating leading companies from the computer and electronics industries. Notable members have included Agere (now merged with LSI Corporation), Apple Inc., Hewlett-Packard, Intel, Microsoft and NEC.
History
The USB 1.0 specification was introduced in 1994. USB was created by the core group of companies that consisted of Intel, Compaq, Microsoft, Digital, IBM, and Northern Telecom. Intel produced the UHCI host controller and open software stack; Microsoft produced a USB software stack for Windows and co-authored the OHCI host controller specification with National Semiconductor and Compaq; Philips produced early USB-Audio; and TI produced the most widely used hub chips. USB was intended to replace the multitude of connectors at the back of PCs, as well as to simplify software configuration of communication devices.
The USB 2.0 specification was released in April 2000 and was standardized by the USB-IF at the end of 2001. Hewlett-Packard, Intel, Lucent (now LSI Corporation since its merger with Lucent spinoff Agere Systems (Lucent has been merged with Alcatel, and became Alcatel-Lucent)), Microsoft, NEC, and Philips jointly led the initiative to develop a higher data transfer rate, 480 Mbit/s, than the 1.0 specification of 12 Mbit/s.
The USB 3.0 specification was released on November 17, 2008 by the USB 3.0 Promoter Group. It has a transfer rate of up to 10 times faster than the USB 2.0 version and has been dubbed the SuperSpeed USB.
Equipment conforming with any version of the standard will also work with devices designed to any previous specification (a property known as backward compatibility).
Device classes
USB defines class codes used to identify a device’s functionality and to load a device driver based on that functionality. This enables a device driver writer to support devices from different manufacturers that comply with a given class code.
Device classes include
 | Click this bar to view the full image. |
Note class 0: Use class information in the Interface Descriptors. This base class is defined to be used in Device Descriptors to indicate that class information should be determined from the Interface Descriptors in the device.
Types of USB connector
| Click this bar to view the full image. |
| Click this bar to view the full image. |
There 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 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
USB-A
The Standard-A type of USB connector takes on the appearance of a flattened rectangle that plugs into downstream-port sockets on the USB host or a hub and receives power. This kind of connector is most frequently seen on cables that are permanently attached to a device, such as one on a cable that connects a keyboard or mouse to the computer.
USB-B
Standard-B connectors—which have a square shape with beveled exterior corners—typically plug into upstream sockets on devices that use a removable cable, e.g. between a hub and a printer. Type B plugs deliver power and are therefore analogous to a power socket. This two-connector scheme prevents a user from accidentally creating a loop.
Mini and micro
Various connectors have been used for smaller devices such as PDAs, mobile phones or digital cameras. These include the now-deprecated[12] (but standardized) Mini-A and the current standard Mini-B, Micro-A, and Micro-B connectors. The Mini-A and Mini-B plugs are approximately 3 by 7 mm, while the Micro plugs have a similar width but approximately half the thickness, enabling their integration into thinner portable devices.
The Micro-USB connector was announced by the USB-IF on January 4, 2007 and the Mini-USB connectors were withdrawn[citation needed]. As of February 2009[update], most available devices and cables still use Mini plugs, but the newer Micro connectors are becoming more widely adopted. The thinner Micro connectors are intended to replace the Mini plugs in new devices including smartphones and personal digital assistants. The Micro plug design is rated for 10,000 connect-disconnect cycles. The Universal Serial Bus Micro-USB Cables and Connectors Specification details the mechanical characteristics of Micro-A plugs, Micro-AB receptacles, and Micro-B plugs and receptacles, along with a Standard-A receptacle to Micro-A plug adapter. The carrier-led Open Mobile Terminal Platform (OMTP) group have recently endorsed micro-USB as the standard connector for data and power on mobile devices.[14] These include various types of battery chargers, allowing Micro-USB to be the single external cable link needed by some devices.
USB OTG Sockets: Mini-AB, Micro-AB
Except for special standard-to-Mini-A and standard-to-Micro-A adapters, USB cables always have an A-connector and a B-connector, on opposite ends. A-connectors can always connect to A-sockets; B-connectors can always connect B-sockets. These sockets all come in standard, mini, and micro versions.
For USB On-The-Go (or 'OTG') support for another socket type is defined: the AB, in both mini and micro versions. It can accept both A and B connector, through careful mechanical design. OTG software detects the difference by use of the ID pin, which is grounded in A-connectors and is otherwise floating. When an A-connector is connected to an AB socket, the socket supplies VBUS power to the cable and starts in the host role. When a B-connector is used, the socket consumes VBUS power and starts in the peripheral or device role. OTG allows those two roles to be switched by software, as needed for the task at hand.
Version history
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-Speed) and 12 Mbit/s (Full-Speed). 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 September 1998.
Fixed problems identified in 1.0, mostly relating to hubs. Earliest revision to be widely adopted.
USB 2.0
Hi-Speed USB LogoUSB 2.0: Released in April 2000.
Added higher maximum speed of 480 Mbit/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-B Connector ECN: Released in October 2000.
Specifications for Mini-B plug and receptacle. 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 1.0: Released in March 2007.
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 1.8A. (Note that this document is not distributed with USB 2.0 specification package.)
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.
High-Speed Inter-Chip USB Electrical Specification Revision 1.0: Released in September 2007.
USB 3.0
On September 18, 2007, Pat Gelsinger demonstrated USB 3.0 at the Intel Developer Forum. The USB 3.0 Promoter Group announced on November 17, 2008, that version 1.0 of the specification has been completed and is transitioned to the USB Implementers Forum (USB-IF), the managing body of USB specifications.[34] This move effectively opens the spec to hardware developers for implementation in future products.
Availability
Consumer products are expected to become available in 2010. Commercial controllers are expected to enter into volume production no later than the first quarter of 2010.[38] NEC is aiming to produce its first USB controller in June 2009, initially priced at USD 15.00
Windows 7 drivers are under development but no public releases have been made available as of May 2009. The Linux Kernel supports USB 3.0 as of version 2.6.30.
Reference: Wikipedia
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