USB

Universal Serial Bus
Year Created : January 1996
Width : 1 bit
Number Of : 127 per host
Devices : Controller
Capacity : 12 or 480 Mbit/s
( 1.5 to 60 MByte/s )
Styles : Serial
Hotplugging? : Yes
External? : Yes

USB redirects here, for other uses, see USB (disambiguation).

In information teknology, Universal Serial Bus ( USB ) is a serial bus standard to interface devices. USB was desaigned to allow many peripherals to be connected using a single standardizes interface socked and to improve the plug and play capabilities by allowing devices to be connected and disconnected without rebooting the computer ( hot swapping ). Other convenlent features include providing power to low consumption devices without the need for an external power supply and allowing many devices to be used without requiring manufacturer specific, individual devices drivers to be installed.
USB is intended to help retire all legacy varieties of serial and parallel ports. USB can connect computer peripherals such as computer mouse, keyboards, PDAs, gamepads and joysticks, scanners, digital cameras, printers, personal media players, and flash drives. For many of those devices USB has become the standard connection method. USB was originally designed for personal computers, but it has become commonplace on other devices such as PDAs and video game consoles. as of 2008, there are about a 2 billion USB devices in the world.
the design of USB is standardized by USB Implemanters Forum ( USB - IF ), an industry standards body incorporating leading companies from the computer and elektronics indutries. notable members have included Agere ( now merged with LSI Corporation ), Apple Ins, Hewlett-Packard, Intel, NEC, And Microsoft.

History

The USB 1.0 specification was introduced in November 1995. was promoted by Intel ( UHCI and open software stack ). Microsoft ( Windows software stack ), Philips ( hub, USB-Audio ), and US Robotics. Originally USB was intended to replace the multitude of connectors at the back of PCs, as well as to simplify software configuriton of communication devices.
The original Apple " Bondi Blue " iMac G3, Introduce 6 May 1998, was the first computer to offer USB ports as standard, including the connector for its new keyboard and mouse. USB 1.1 came out in September 1998 to help rectify the adoption problems that occurred with earlier iterations of USB.
As of 2008 the USB specification is at version 2.0 ( with revisions ). Hewlett-Packard, Intel, Lucent ( now Alcatel-lucent ), Microsoft, NEC, and Philips jointly led the initiative to develop a higher data transfer rate than the 1.1 specification. he USB 2.0 specification was released in April 2000 and was standardized by the USB-IF at the end of 2001. equipment conforming with any version of the standard will also work with devices designed to any previous specification ( known as backward compatibility ).
Smaller USB plug s and receptacles for use in handheld and mobile device, called Mini-B, were added to USB specification in the first engineering change notice. A new variant of smaller USB plug and receptacles, Micro-USB, was announced by the USB Implementers Forum on january 4,2007

Types Of USB Connector

There are saveral types Of USB connectors, and some have been added as the specification has progressed. The original USB specification detailed standard-A and standard-B plug and receptacles. The first engineering change notice to the USB 2.0 specification added Mini-B plug and receptacles. The data slot in A-plug are actually farther in the plug than the outside power wires to prevent data errors by powering the devices first, then transferring data.

The enhanced mini-USB, mini-B, micro-A, Micro-B, and Micro-AB connectors are used for smaller device such as PDAs, mobile phones or digital cameras. the standard-A plug is approximately 4 by 12 mm, the standard-B approximately 2 by 7 mm.

micro-USB is a further connector, that was announced by the USB-IF on january 4,2007. it is intended to replace the mini-USB plug used in many new smartphones and personal digital assistants. this micro-USB plug is rated for 10.000 connected-disconnected cycles. it is about half the height of the mini-USB connector, but featured similiar width. in he Universal Serial Bus Micro-USB Cables and connectors specification, details have been laid down for Micro-A plugs, Micro-AB receptacles, and Micro-B plugs and receptacles, along with a standard-A receptacles to micro-A plug adapter. the carier led group OMTP have recently endorsed micro-USB as the standard connector for data and power on mobile devices.

microsoft's original Xbox game console uses standard USB 1.1 signaling in its controller and memory cards, but features propietary connectors and ports. similiarly, IBM Ultraport uses standard USB signaling, but via proprietary connection format. American Power Conversion uses USB signaling and HID device class on its uninterruptible power supplies using 10P10C connector to carry USB, audio, or power sgnals. many digital cameras have a tiny 8 pin connector that combines USB with video and audio out.

Over View

A USB system has anasymatric design, consisting of a host, a multitude of downstream USB ports, and multiple peripheral devices connected in a tired-star topology. Addititional USB may be included in tiers,allowing brranching into a tree structure, subject to a limit of 5 levelsof tiers. USB host may have multuple host controller and each host controller may provide one or more USB ports. Up to 127 devices, includng the hub devices, may be connectedto single host controller.

USB device are linked in series through hubs. there always exists one hub known as the root hub, wihich is built-in to the controller. So-called " Shering Hubs ", which allow multiple computers to access the same peripheral device( s ), also exist and work by either switching access between PCs automatically or manually. They are popular in small-office environments. in network terms, they converge rather than diverge branches.

A single physical USB device may consist of saveral logical sub-devices that are refrred to as device functions, because each indivudual device may provide several fuctions, such as a webcam ( video device function ) with a built-inmicrophone ( audio device function ).

USB device communication is based on pipes ( logical shannels ). pipes are connections from the host controller to a logicalentity on the device named an endpoint. The term endpoint is also occasionally used refer tithe pipe. A USB device can have up to 32 active pipes, 16 intothe host controller and 16 out the controller. Each endpoint can transfer data in one direction only, either intoor out of the device, so each pipe is uni-directional. Endpoints are grouped into interface and each interface is associated with a single device configuration and which is not associated with any interface.

When new USB device is connected to a USB host, the USB device enumeration process is started. The enumeration process first sends a reset signaling to be USB device. The speed of USB device is determined during the reset signaling. After reset, USB device setup information is read from the device by the host and the device is a assigned a unique host-controller-specific 7-bit addres. 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 configured state. If the USB host is restarted, the enumeration process is repeated for all connected devices.

The host controller polls the bus for traffic, usually in a round-robin fashion, so noUSB device can transfer any data on the bus without an explicit request from the host controller.

USB Signaling

USB supports three data rates :

• A Low Speed ( 1.1, 2.0 ) rate of 1.5 Mbit/s ( 187.5 kB/s ) that is mostly used for Human Interface Devices ( HID ) such as keyboards, mice, and joysticks.
• A Full Speed ( 1.1, 2.0 ) rate of 12 Mbit/s ( 1.5 MB/s ). full was the fastest rate before the USB 2.0 specification and many devices fall back to full Speed. Full Speed devices dividethe USB bandwidth between them in a first-come first-sarved basis and it is not uncommon to run out of bandwidth with saveral isochronous devices. All USB hubs support Full Speed.
• A High-Speed ( 2.0 ) rate 480 Mbit/s ( 60 MB/s ).

Experimental data rate :

• A Super-Speed ( 3.0 ) rate of 4.8 Gbit/s ( 600 MB/s ). The USB 3.0 Specification will be released by Intel and its partners in mid-2008, according to early reports from CNET news. According to Intel, bus speeds will be 10 times faster than USB 2.0 due to the inclusion of the 3.0 specification are likely to arrive in 2009 or 2010.

USB signaling are transmitted on a twisted pair data cable with 90 ohm or 15% impedance, labeled D+ and D-. these collectively use half-duplex diferential signaling to combat the effects of electromagnetic noise on longer lines. D+ and D- usually operate together; they are not separate simplex connections. Transmitted signal levels are 0.0-0.3 volts for low and 2.8-3.6 volts for high in Full Speed and Low Speed modes, ( and 400mV in High Speed ( HS ) mode ). In FS mode the cable wires are not terminated, but the HS mode has termination of 45 ohm to ground, or 90 ohm differential to match the data cable impedance.

USB uses a special protocol called " chirping " to negotiate the High-Speed mode. In simplified terms, a device that is HS capable always connects as an FS device first, but after receiving a USB RESET ( both D+ and D- are driven LOW by host ) it tries to pull the D- line high. If the host ( or hub ) is also HS capable, it returns alternating signaling on D- and D+ lines letting the device know that the tier will operate at High Speed. Clock tolerance is 480.00 Mbit/s or 500ppm, 12.000 Mbit/s or 25000ppm, 1.50 Mbit/s or 15000ppm
The USB standard uses the NRZI system to encode data, and uses " bit stufing " by always injecting one artificial " zero " bit if the stream of data contains six consecutive " ones " before converting the bit stream to NRZI.
Though Hi-Speed devices are commonly referred to as " USB 2.0 " and advertised as " up to 480 Mbit/s ", not all USB 2.0 devices are Hi-Speed. The USB-IF cetifies devices and provides licenses to use special marketing logos for either " basic-speed" ( low and full ) or Hi-Speed after passing a compliance test and paying a licensing fee. All device are tested according to the latest spec, so recently-compliant Low-Speed devices are also 2.0 devices.
The actual throughput currently ( 2006 ) attained with real devices is about two thirds of the maximum theoretical bulk data transfer rate of 53.248 MB/s. Typical hi-speed USB devices operate at lower speeds, often about 3 MB/s overall, sometimes up to 10-20 MB/s.

USB Protocol Analyzer
Due to the complexities of the USB protocol, USB protocol analyzers are invaluable tools to people developing USB devices. USB analyzers are able to capture the data on USB and display information from low-levelbus states high-level data packets and class-level information.