INTRODUCTIONUniversal Serial Bus (USB) is a serial bus standard to connect devices to a host computer. The USB 3.0 is the upcoming version of the USB. The USB 3.0 is also called super speed USB. Because the USB 3.0 support a raw throughput of 500MByte/s. As its previous versions it also support the plug and play capability, hot swapping etc. USB was designed to allow many peripherals to be connected using a single standardized interface socket. . 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.
There are many new features included in the new Universal Serial Bus Specification. The most important one is the supers speed data transfer itself. Then the USB 3.0 can support more devices than the currently using specification which is USB 2.0. The bus power spec has been increased so that a unit load is 150mA (+50% over minimum using USB 2.0). An unconfigured device can still draw only 1 unit load, but a configured device can draw up to 6 unit loads (900mA, an 80% increase over USB 2.0 at a registered maxim um of 500mA). Minimum device operating voltage is dropped from 4.4V to 4V. When operating in Super Speed mode, full-duplex signaling occurs over 2 differential pairs separate from the non-SuperSpeed differential pair. This result in USB 3.0 cables containing 2 wires for power and ground, 2 wires for non-Super Speed data, and 4 wires for SuperSpeed data, and a shield (not required in previous specifications).
HISTORY
PRE-RELEASES:
I. USB 0.7: Released in November 1994.
II. USB 0.8: Released in December 1994.
III. USB 0.9: Released in April 1995.
IV. USB 0.99: Released in August 1995.
V. USB 1.0: Released in November 1995.
USB 1.0I. 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 ex tension cables or pass-through monitors (due to timing and power limitations). Few such devices actually made it to market.
II. 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
1. USB 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:
I. 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
II. Pull-up/Pull-down Resistors ECN: Released in May 2002.
III. Interface Associations ECN: Released in May 2003.
New standard descriptor was added that allows multiple interfaces to be
associated with a single device function.
IV. Rounded Chamfer ECN: Released in October 2003.
A recommended, compatible change to Mini-B plugs that results in longer lasting connectors
V. Inter-Chip USB Supplement: Released in March 2006.
VI. 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 re quiring a separate USB host. In practice, one of the USB devices acts as a host for the other device.
VII. 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 distrib uted with USB 2.0 specification package.)
VIII. Micro-USB Cables and Connectors Specification 1.01: Released in April 2007.
IX. Link PowerManagementAddendum 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.
X. High-Speed Inter-Chip USB Electrical Specification Revision 1.0: Released in September 2007.
USB 3.0On 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. This move effectively opens the spec to hardware developers for implementation in future products.
Features1. A new major feature is the "SuperSpeed" bus, which provides a fourth transfer mode at 4.8 Gbit/s. The raw throughput is 4 Gbit/s, and the specification considers it reasonable to achieve 3.2 Gbit/s (0.4 GByte/s or 400 MByte/s) or more after protocol overhead.
2. When operating in SuperSpeed mode, full-duplex signaling occurs over 2 differential pairs separate from the non-SuperSpeed differential pair. This results in USB 3.0 cables containing 2 wires for power and ground, 2 wires for non-SuperSpeed data, and 4 wires for SuperSpeed data, and a shield (not required in previous specifications).
3. To accommodate the additional pins for SuperSpeed mode, the physical form factors for USB 3.0 plugs and receptacles have been modified from those used in previous versions. Standard-A cables have extended heads where the SuperSpeed connectors extend beyond and slightly above the legacy connectors. Similarly, the Standard-A receptacle is deeper to accept these new connectors. On the other end, the SuperSpeed Standard-B connectors are placed on top of the existing form factor. A legacy standard A-to-B cable will work as designed and will never contact any of the SuperSpeed connectors, ensuring backward compatibility. SuperSpeed standard A plugs will fit legacy A receptacles but SuperSpeed standard B plugs will not fit into legacy standard B receptacles (so a new cable can be used to connect a new device to an old host but not to connect a new host to an old device; for that, a legacy standard A-to-B cable will be required)
4. SuperSpeed establishes a communications pipe between the host and each device, in a host-directed protocol. In contrast, USB 2.0 broadcasts packet traffic to all devices.
5. USB 3.0 extends the bulk transfer type in SuperSpeed with Streams. This extension allows a host and device to create and transfer multiple streams of data through a single bulk pipe.
6. New power management features include support of idle, sleep and suspend states, as well as Link-, Device-, and Function-level power management.
7. The bus power spec has been increased so that a unit load is 150 mA (+50% over minimum using USB 2.0). An unconfigured device can still draw only 1 unit load, but a configured device can draw up to 6 unit loads (900 mA, an 80% increase over USB 2.0 at a registered maximum of 500 mA). Minimum device operating voltage is dropped from 4.4 V to 4 V.
8. USB 3.0 does not define cable assembly lengths, except that it can be of any length as long as it meets all the requirements defined in the specification. However, electronicdesign.com estimates cables will be limited to 3 m at SuperSpeed.
9. Technology is similar to a single channel (1x) of PCI Express 2.0 (5-Gbit/s). It uses 8B/10B encoding, linear feedback shift register (LFSR) scrambling for data and spread spectrum. It forces receivers to use low frequency periodic signaling (LFPS), dynamic equalization, and training sequences to ensure fast signal locking.
10. External Hard Drive supports USB 3.0 standard.
My Book 3.0 desktop external drive features SuperSpeed USB 3.0 compliant interface that provides transfer rates of up to 5 Gbps. Windows® PC drive is also backwards compatible with USB 2.0 and USB 1.1. Device supports resource-intensive video editing, animation, and graphic design applications and is offered standalone or in kit with USB 3.0 PCIe adapter card. One and two terabyte models are available.
OVERVIEWA USB system has an asymmetric design, 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 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. So-called sharing hubs, which allow multiple computers to access the same peripheral device(s), also exist and work by switching access between PCs, either automatically or manually. Sharing hubs are popular in small-office environments. In network terms, they converge rather than diverge branches.
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. The term endpoint is occasionally incorrectly used for referring to the pipe. However, while an endpoint exists on the device permanently, a pipe is only formed when the host makes a connection to the endpoint. Therefore, when referring to a particular connection between a host and a USB device function, the term pipe should be used. A USB device can have up to 32 endpoints: 16 into the host controller and 16 out of the host controller. But, as one of the pipes is required to be of a bi-directional type (the default control pipe), and thus uses 2 endpoints, the theoretical maximum number of pipes is 31. 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 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 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 CLASSESUSB3 defines class codes used to identify a device’s functionality and to load a device driver based on that functionality. This enables every device driver writer to support devices from different manufacturers that comply with a given class code.
Device classes include:
Class Usage Description Examples
00h
Device Unspecified[8]
(Device class is unspecified. Interface descriptors are used for determining the required 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 (This class is 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),[9] USB DFU (Direct Firmware update)[10]
FFh Both Vendor-specific (This class code indicates that the device needs vendor specific drivers.)
USB mass storageA 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 (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 flash drives. 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 SD card with a USB adapter is particular advantageous for maintaining the integrity and non-corruptible, pristine state of the booting medium. A live USB OS, resident on a write-locked SD card is impervious to modification by computer viruses or ill-conditioned software
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 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, etc.), several manufacturers offer external portable USB hard 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 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 (IDE, ATA, SATA, PATA, ATAPI, or even SCSI) 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) without requiring installation on the host computer.
Human interface devices (HIDs)
Mice and keyboards usually have USB connectors. These can 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 devices are also progressively migrating from MIDI, and PC game port connectors to USB. designed to detect whether it is connected to a USB or PS/2 port, and communicate using the appropriate protocol.
Joysticks, keypads, tablets and other human-interface
CONNECTOR PROPERTIES
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.On September 24, 2009 Freecom announced a USB 3.0 external hard drive.
On October 27, 2009 Gigabyte Technology announced 7 new P55 chipsets motherboards that included onboard USB 3.0, SATA Rev. 3 (6Gb/s) and triple power to all USB ports.On January 6th, 2010 ASUS was the first manufacturer to release a USB 3.0-certified motherboard, the P6X58D Premium.To ensure compatibility between motherboards and peripherals, all USB-certified devices must be approved by the USB Implementers Forum.
Drivers are under development for Windows 7, but support was not included with the initial release of the operating system.The Linux kernel has supported USB 3.0 since version 2.6.31, which was released in September 2009.
At least one complete end-to-end test system for USB3 designers is now on the market.
Intel will not support usb 3.0 until 2011
This will slow down mainstream adoption. These delays may be due to problems in the CMOS manufacturing process, a focus to advance the Nehalem platform or a tactic by Intel to boost its upcoming Light Peak interface. Current AMD roadmaps indicate that the new southbridges released in the beginning of 2010 will not support USB 3.0. Market researcher In-Stat predicts a relevant market share of USB 3.0 not until 2011.
January 4, 2010, Seagate announced a small portable HDD with PC Card targeted for laptops (or desktop with PC Card slot addition) at the CES in Las Vegas.
Usability1. It is deliberately difficult to attach a USB connector incorrectly. Most connectors cannot be plugged in upside down, and it is clear from the appearance and kinesthetic sensation of making a connection when the plug and socket are correctly mated. However, it is not obvious at a glance to the inexperienced user (or to a user without sight of the installation) which way around the connector goes, thus it is often necessary to try both ways. More often than not, however, the side of the connector with the trident logo should be on "top" or "toward" the user. Most manufacturers do not, however, make the trident easily visible or detectable by touch.
2. Only moderate insertion / removal force is needed (by specification). USB cables and small USB devices are held in place by the gripping force from the receptacle (without need of the screws, clips, or thumbturns other connectors have required).
3. The force needed to make or break a connection is modest, allowing connections to be made in awkward circumstances (ie, 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).
4. 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.
Durability1. The standard connectors were designed to be robust. Many previous connector designs were fragile, specifying embedded component pins or other delicate parts which proved liable to bending or breaks, even with the application of only very modest force. The electrical contacts in a USB connector are protected by an adjacent plastic tongue, and the entire connecting assembly is usually further protected by an enclosing metal sheath. As a result USB connectors can safely be handled, inserted, and removed, even by a young child.
2. 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 any potentially damaging static charges (rather than via delicate electronic components). This enclosure design also means that there is a (moderate) degree of protection from electromagnetic interference afforded to the USB signal while it travels through the mated connector pair (this is the only location when the otherwise twisted data pair must travel a distance 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.
3. The newer Micro-USB receptacles are designed to allow 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.
Compatibility
1. The USB standard specifies relatively loose tolerances for compliant USB connectors, intending to minimize incompatibilities in connectors produced by different vendors (a goal that has been very successfully achieved). Unlike most 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.
2. 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 (ie, 1.x or 2.0), all communication is half-duplex and directionally controlled by the host.
3. USB 3.0 receptacles are electrically compatible with USB 2.0 device plugs if they can physically match. Most combinations will work, but there are a few physical incompatibilities. However, only USB 3.0 Standard-A receptacles can accept USB 3.0 Standard-A device plugs.
4. In general, cables have only plugs (very few have a receptacle on one end), 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.
CONNECTOR TYPESPinouts of Standard, Mini, and Micro USB connectors
Different types of USB connectors from left to right:
• male micro USB
• male mini USB B-type
• male B-type
• female A-type
• male A-type
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-AThe 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-BA 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 printer. 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 electrical loop.
Pin configuration of the USB connectors Standard A/B, viewed from face of plug
COMPARISONS WITH OTHER DEVICE CONNECTION TECHNOLOGIES1. FireWire
USB was originally seen as a complement to FireWire (IEEE 1394), which was designed as a high-bandwidth serial bus which could efficiently interconnect peripherals such as hard disks, audio interfaces, and video equipment. USB originally operated at a far lower data rate and used much simpler hardware, and was suitable for small peripherals such as keyboards and mice.
The most significant technical differences between FireWire and USB include the following:
I. USB networks use a tiered-star topology, while FireWire networks use a tree topology.
II. USB 1.0, 1.1 and 2.0 use a "speak-when-spoken-to" protocol. Peripherals cannot communicate with the host unless the host specifically requests communication. USB 3.0 is planned to allow for device-initiated communications towards the host (see USB 3.0 below). A FireWire device can communicate with any other node at any time, subject to network conditions.
III. A USB network relies on a single host at the top of the tree to control the network. In a FireWire network, any capable node can control the network.
IV. USB runs with a 5 V power line, while Firewire (theoretically) can supply up to 30 V.
V. Standard USB hub ports can provide from the typical 500mA[2.5 Watts] of current, only 100mA from non-hub ports.
VI. USB 3.0 & USB On-The-Go 1800mA[9.0W] (for dedicated battery charging, 1500mA[7.5W] Full bandwidth or 900mA[4.5W] High Bandwidth), while FireWire can in theory supply up to 60 watts of power, although 10 to 20 watts is more typical.
These and other differences reflect the differing design goals of the two buses: USB was designed for simplicity and low cost, while FireWire was designed for high performance, particularly in time-sensitive applications such as audio and video. Although similar in theoretical maximum transfer rate, FireWire 400 has performance advantage over USB 2.0 Hi-Bandwidth in real-use, especially in high-bandwidth use such as external hard-drives.
The newer FireWire 800 standard being twice as fast as FireWire 400 outperforms USB 2.0 Hi-Bandwidth both theoretically and practically.The chipset and drivers used to implement USB and Firewire have a crucial impact on how much of the bandwidth prescribed by the specification is achieved in the real world, along with compatibility with peripherals.
2. Power over Ethernet
The 802.3af Power over Ethernet has superior power negotiation and optimization capabilities to powered USB. Power over Ethernet also supplies more power because it operates at 48V, 720mA while USB operates at 5V, 500mA. Ethernet also operates many more meters, with significant DC power loss, and will remain accordingly the preferred option for VoIP, security camera and other applications where networks extend through a building. However, USB is preferred when cost is critical.
3. Digital musical instruments
Digital musical instruments are another example of where USB is competitive for low-cost devices. However power over ethernet and the MIDI plug standard are preferred in high-end devices that must work with long cables. USB can cause ground loop problems in audio equipment because it connects the ground signals on both transceivers. By contrast, the MIDI plug standard and ethernet have built-in isolation to 500V or more.
CABLESThe maximum length of a standard USB cable (for USB 2.0 or earlier) is 5.0 metres (16.4 ft). The primary reason for this limit is the maximum allowed round-trip delay of about 1,500 ns. 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 be 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 bandwidth for standard copper cable). This allows for a 5 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 3m.
No fiber optic cable designs are known to be under development, but they would be likely to have a much longer maximum allowable length, and more complex construction.
The data cables for USB 1.x and USB 2.x use a twisted pair to reduce noise and crosstalk. They are arranged much as in the diagram below. USB 3.0 cables are more complex and employ shielding for some of the added data lines (2 pairs); a shield is added around the pair sketched.
Fig 9.
Pin Name Cable color Description
1 VCC
Red +5 V
2 D− White Data −
3 D+ Green Data +
4 GND
Black Ground
USB 1.x/2.0 cable wiring
Pin Name Color Description
1 VCC Red +5 V
2 D− White Data −
3 D+ Green Data +
4 ID none permits distinction of
Micro-A- and Micro-B-Plug
Type A: connected to Ground
Type B: not connected
5 GND Black Signal Ground
USB 1.x/2.0 Miniplug/Microplug
MAXIMUM USEFUL DISTANCEUSB 1.1 maximum cable length is 3 metres (9.8 ft) and USB 2.0 maximum cable length is 5 metres (16 ft). Maximum permitted hubs connected in series is 5. Although a single cable is limited to 5 metres, the USB 2.0 specification permits up to five USB hubs in a long chain of cables and hubs. This allows for a maximum distance of 30 metres (98 ft) between host and device, using six cables 5 metres (16 ft) long and five hubs. In actual use, since some USB devices have built-in cables for connecting to the hub, the maximum achievable distance is 25 metres (82 ft) + the length of the device's cable. For longer lengths, USB extenders that use CAT5 cable can increase the distance between USB devices up to 50 metres (160 ft).
A method of extending USB beyond 5 metres (16 ft) is by using low resistance cable.The higher cost of USB 2.0 Cat 5 extenders has urged some manufacturers to use other methods to extend USB, such as using built-in USB hubs, and custom low-resistance USB cable. It is important to note that devices which use more bus power, such as USB hard drives and USB scanners will require the use of a powered USB hub at the end of the extension, so that a constant connection will be achieved. If power and data does not have sufficient power then problems can result, such as no connection at all, or intermittent connections during use.
USB 3.0 cable assembly may be of any length as long as all requirements defined in the specification are met. However, maximum bandwidth can be achieved across a maximum cable length of approximately 3 metres.
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 V to 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.
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. A battery-powered hub may supply maximum unit loads to ports. In addition, the VBUS 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 1500 mA by default.
A Dedicated Charging Port can supply a maximum of 1.8 A of current at 5.25 V. A portable device can draw up to 1.8 A from a Dedicated Charging Port. The Dedicated Charging Port shorts the D+ and D- pins with a resistance of at most 200Ω. The short disables data transfer, but allows devices to detect the Dedicated Charging Port and allows very simple, high current chargers to be manufactured.
Powered USB
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.
This is commonly used in retail systems and provides enough power to operate stationary barcode scanners, printers, pin pads, signature capture devices, etc. This modification of the USB interface is proprietary and was developed by IBM, NCR, and FCI/Berg.
It is essentially two connectors stacked such that the bottom connector accepts a standard USB plug and the top connector takes a power connector.
Sleep and Charge
Sleep-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 a new standard charger for mobile phones.
Close-up of a Micro-B plug
As of June 14, 2007, all new mobile phones applying for a license in China 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 Open Mobile Terminal Platform group—a forum of mobile network operators and manufacturers such as Nokia, Samsung, Motorola, Sony Ericsson and LG—announced that its members had agreed on micro-USB as the future common connector for mobile devices.
On February 17, 2009, the GSM Association 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. The basis of the GSMA's Universal Charger Solution (UCS) is the technical recommendation from OMTP and the USB-IF battery charging standard.
On April 22, 2009, this was further endorsed by the CTIA – The Wireless Association.
On June 29, 2009 the European Commission announced an agreement with ten producers that starting in 2010, data-enabled mobile phones sold in the European Union would include a micro-USB connector for recharge.
On October 22, 2009 the International Telecommunication Union (ITU) announced that it had embraced the Universal Charger Solution as its "energy-efficient one-charger-fits-all new mobile phone solution", and added: "Based on the Micro-USB interface, UCS chargers will also include a 4-star or higher efficiency rating—up to three times more energy-efficient than an unrated charger.
Non-standard devicesUSB vacuum cleaner novelty device
Some USB devices require more power than is permitted by the specifications for a single port. This is common for external hard and optical disc drives, and generally for devices with motors or lamps. Such devices can use an external power supply, which is allowed by the standard, or use a dual-input USB 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 USB decorations. The typical example is a USB-powered keyboard light; fans, mug coolers and heaters, battery chargers, miniature vacuum cleaners, and even miniature lava lamps 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 hurting 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 inrush current (i.e., that used to charge decoupling and filter capacitors) when the device is first connected. Otherwise, connecting a device could cause problems with the host's internal power. 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. Some of these devices can supply up to 1 A of current.
USB 2.0 DATA RATES
The 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 Southbridge. Big performance gains can be achieved when attaching multiple high bandwidth USB devices such as disk enclosures in different controllers. The following table displays Southbridge ICs that have multiple EHCI controllers.
Vendor
Southbridge
USB 2.0 Ports
EHCI Controllers
Maximum
Data Rate Rate
AMD
SB7x0/SP5100
12 2 120 MB/s
AMD SB8x0 14 3 180 MB/s
Broadcom
HT1100 12 3 180 MB/s
Intel
ICH8 10 2 120 MB/s
Intel ICH9 12 2 120 MB/s
Intel ICH10 12 2 120 MB/s
Intel PCH
8/12/14 2 120 MB/s
nVIDIA
ION/ION-LE
12 2 120 MB/s
Every other AMD, Broadcom, Intel southbridge supporting USB 2.0 has only one EHCI controller. All SiS southbridge supporting USB 2.0 have only one EHCI controller. All ULi, VIA southbridge, single chip northbridge/southbridge supporting USB 2.0 have only one EHCI controller.
Also all PCI USB 2.0 ICs used for add-in cards have only one EHCI controller. Despite that some card manufacturers offer improved cards which have 2 PCI USB 2.0 ICs attached to one PCI to PCI bridge.
In PCIe, the usual design with multiple USB ports per EHCI controller has changed with the introduction of the MosChip MCS9990 IC. MCS9990 has one EHCI controller per port so all its USB ports can operate simultaneously without any performance limitations. Dual IC cards have been introduced as well and come with 2 PCI USB 2.0 ICs attached to one PCI to PCIe bridge.
DATA PACKETSUSB communication takes the form of packets. Initially, all packets are sent from the host, via the root hub and possibly more hubs, to devices. Some of those packets direct a device to send some packets in reply.
After the sync field, all packets are made of 8-bit bytes, transmitted least-significant bit first. The first byte is a packet identifier (PID) byte. The PID is actually 4 bits; the byte consists of the 4-bit PID followed by its bitwise complement. This redundancy helps detect errors. (Note also that a PID byte contains at most four consecutive 1 bits, and thus will never need bit-stuffing, even when combined with the final 1 bit in the sync byte. However, trailing 1 bits in the PID may require bit-stuffing within the first few bits of the payload.)
USB PID bytes
Type PID value
(msb-first) Transmitted byte
(lsb-first) Name Description
Reserved 0000 0000 1111
Token 1000 0001 1110 SPLIT High-bandwidth (USB 2.0) split transaction
0100 0010 1101 PING Check if endpoint can accept data (USB 2.0)
Special 1100 0011 1100 PRE Low-bandwidth USB preamble
Handshake ERR Split transaction error (USB 2.0)
0010 0100 1011 ACK Data packet accepted
1010 0101 1010 NAK Data packet not accepted; please retransmit
0110 0110 1001 NYET Data not ready yet (USB 2.0)
1110 0111 1000 STALL Transfer impossible; do error recovery
Token 0001 1000 0111 OUT Address for host-to-device transfer
1001 1001 0110 IN Address for device-to-host transfer
0101 1010 0101 SOF Start of frame marker (sent each ms)
1101 1011 0100 SETUP Address for host-to-device control transfer
Data 0011 1100 0011 DATA0 Even-numbered data packet
1011 1101 0010 DATA1 Odd-numbered data packet
0111 1110 0001 DATA2 Data packet for high-bandwidth isochronous transfer (USB 2.0)
1111 1111 0000 MDATA Data packet for high-bandwidth isochronous transfer (USB 2.0)
Packets come in three basic types, each with a different format and CRC (cyclic redundancy check):
1. Handshake packets
Handshake packets consist of nothing but a PID byte, and are generally sent in response to data packets. The three basic types are ACK, indicating that data was successfully received, NAK, indicating that the data cannot be received at this time and should be retried, and STALL, indicating that the device has an error and will never be able to successfully transfer data until some corrective action (such as device initialization) is performed.
USB 2.0 added two additional handshake packets, NYET which indicates that a split transaction is not yet complete. A NYET packet is also used to tell the host that the receiver has accepted a data packet, but cannot accept any more due to buffers being full. The host will then send PING packets and will continue with data packets once the device ACK's the PING. The other packet added was the ERR handshake to indicate that a split transaction failed.
The only handshake packet the USB host may generate is ACK; if it is not ready to receive data, it should not instruct a device to send any.
2. Token packets
Token packets consist of a PID byte followed by 2 payload bytes: 11 bits of address and a 5-bit CRC. Tokens are only sent by the host, never a device.
IN and OUT tokens contain a 7-bit device number and 4-bit function number (for multifunction devices) and command the device to transmit DATAx packets, or receive the following DATAx packets, respectively.
An IN token expects a response from a device. The response may be a NAK or STALL response, or a DATAx frame. In the latter case, the host issues an ACK handshake if appropriate.
An OUT token is followed immediately by a DATAx frame. The device responds with ACK, NAK, NYET, or STALL, as appropriate.
SETUP operates much like an OUT token, but is used for initial device setup. It is followed by an 8-byte DATA0 frame with a standardized format.
Every millisecond (12000 full-bandwidth bit times), the USB host transmits a special SOF (start of frame) token, containing an 11-bit incrementing frame number in place of a device address. This is used to synchronize isochronous data flows. High-bandwidth USB 2.0 devices receive 7 additional duplicate SOF tokens per frame, each introducing a 125 µs "microframe" (60000 high-bandwidth bit times each).
USB 2.0 added a PING token, which asks a device if it is ready to receive an OUT/DATA packet pair. The device responds with ACK, NAK, or STALL, as appropriate. This avoids the need to send the DATA packet if the device knows that it will just respond with NAK.
USB 2.0 also added a larger 3-byte SPLIT token with a 7-bit hub number, 12 bits of control flags, and a 5-bit CRC. This is used to perform split transactions. Rather than tie up the high-bandwidth USB bus sending data to a slower USB device, the nearest high-bandwidth capable hub receives a SPLIT token followed by one or two USB packets at high bandwidth, performs the data transfer at full or low bandwidth, and provides the response at high bandwidth when prompted by a second SPLIT token. The details are complex; see the USB specification.
3. Data packets
A data packet consists of the PID followed by 0–1023 bytes of data payload (up to 1024 in high bandwidth, at most 8 at low bandwidth), and a 16-bit CRC.
There are two basic data packets, DATA0 and DATA1. They must always be preceded by an address token, and are usually followed by a handshake token from the receiver back to the transmitter. The two packet types provide the 1-bit sequence number required by Stop-and-wait ARQ. If a USB host does not receive a response (such as an ACK) for data it has transmitted, it does not know if the data was received or not; the data might have been lost in transit, or it might have been received but the handshake response was lost.
To solve this problem, the device keeps track of the type of DATAx packet it last accepted. If it receives another DATAx packet of the same type, it is acknowledged but ignored as a duplicate. Only a DATAx packet of the opposite type is actually received.
When a device is reset with a SETUP packet, it expects an 8-byte DATA0 packet next.
USB 2.0 added DATA2 and MDATA packet types as well. They are used only by high-bandwidth devices doing high-bandwidth isochronous transfers which need to transfer more than 1024 bytes per 125 µs "microframe" (8192 kB/s).
PRE "packet"
Low-bandwidth devices are supported with a special PID value, PRE. This marks the beginning of a low-bandwidth packet, and is used by hubs which normally do not send full-bandwidth packets to low-bandwidth devices. Since all PID bytes include four 0 bits, they leave the bus in the full-bandwidth K state, which is the same as the low-bandwidth J state. It is followed by a brief pause during which hubs enable their low-bandwidth outputs, already idling in the J state, then a low-bandwidth packet follows, beginning with a sync sequence and PID byte, and ending with a brief period of SE0. Full-bandwidth devices other than hubs can simply ignore the PRE packet and its low-bandwidth contents, until the final SE0 indicates that a new packet follows.
SIGNALINGUSB supports following signaling rates:
1. A low-bandwidth 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 human interface devices (HID) such as keyboards, mice, and joysticks.
2. The full-bandwidth rate of 12 Mbit/s (~1.43 MB/s) is the basic USB data rate defined by USB 1.1. All USB hubs support full-bandwidth.
3. A hi-bandwidth (USB 2.0) rate of 480 Mbit/s (~57 MB/s) was introduced in 2001. All hi-bandwidth devices are capable of falling back to full-bandwidth operation if necessary; they are backward compatible. Connectors are identical.
4. 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 NEC May 2009 and products using the 3.0 specification are expected to arrive beginning in Q3 2009 and 2010.USB 3.0 connectors are generally backwards compatible, but include new wiring and full duplex operation.
Prior to USB 3.0, these collectively use half-duplex differential signaling to reduce the effects of electromagnetic noise on longer lines. Transmitted signal levels are 0.0–0.3 volts for low and 2.8–3.6 volts 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.
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.
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 USB-IF certifies devices and provides licenses to use special marketing logos for either "basic bandwidth" (low and full) or high bandwidth after passing a compliance test and paying a licensing fee. All devices are tested according to the latest specification, so recently-compliant low bandwidth devices are also 2.0 devices.
The actual throughput currently (2006) of USB 2.0 high bandwidth attained with real-world devices is about two thirds of the maximum theoretical bulk data transfer rate of 53.248 MiB/s. Typical high bandwidth USB devices operate at lower data rates, often about 3 MiB/s overall, sometimes up to 10–20 MiB/s.
ARCHITECTUREARCHITECTURAL COMPONENTSHUBThe hub provide electrical interface between the USB devices and the host. Hubs are directly responsible for supporting many of the attributes that make USB user friendly and hide its complexity from the user. Listed below the major aspects of USB functionality that hub support:
III. Connectivity behavior
IV. Power management
V. Device connect/disconnect detection
VI. Bus fault detection
VII. Superspeed and USB2.0 (high-speed, full-speed, an low-speed) support
USB 3.0 hub incorporates a USB 2.0 hub and a SuperSpeed hub consisting of two principal components: the SuperSpeed Hub Repeater/Forwarder and the SuperSpeed Hub controller. The hub repeater/forwarder is responsible for connectivity and setup and tear-down. It also support fault detection and recovery. The Hub controller provides the mechanism for host-hub communication. Hub-specific status and control commands permit the host to configure hub and to monitor and control its individual downstream port.
HOSTThere are two hosts are incorporated in a USB 3.0 host. One is SuperSpeed host and the second one is Non-SuperSpeed host. This incorporation ensures the backward compatibility of the USB 3.0 hub. Here the SuperSpeed hub will be supporting the 500MB/sec data transfer rate with full duplex mode. Then the Non-SuperSpeed host will be supporting the old data rates such as High-Speed, Full-Speed, Low-Speed. The host here interacts with the devices by the help of a host controller.
When the host is powered off, the hub does not provide power to is downstream unless the hub support the charging application. When the host is powered on with SuperSpeed support enabled on its downstream port by default the following is the typical sequence of events.
Hub detects VBUS SuperSpeed support and powers its downstream ports with SuperSpeed enabled.
VIII. Hub connects both as s SuperSpeed and as a High-Speed device.
IX. Device detects VBUS and SuperSpeed support and connects as a SuperSpeed device.
X. Host system begins hub enumeration at high-speed and SuperSpeed.
XI. Host system begins device enumeration at SuperSpeed.
1. SuperSpeed host is a source or sink of information. It implements the required host-end, SuperSpeed. Communications layer to accomplish information exchanges over the bus.
It owns the SuperSpeed data activity schedule and management of the SuperSpeed bus and all devices connected to it. The host includes an implementation number of the root downstream ports for SuperSpeed and USB 2.0. Through these ports the host:
XII. Detect the attachment and removal of USB device
XIII. Manages control flow between the host and the USB device
XIV. Manages data flow between the host and the USB device
XV. Collect the status activity statistics
XVI. Provide power to the attached USB device
DEVICE
SuperSpeed devices are sources or sink of information exchanges. They implement the required device-end, SuperSpeed communication layers to accomplish information exchanges between a driver on the host and a logical function on the device. All SuperSpeed devices share their base architecture with USB 2.0.
They are required to carry information for self-identification and generic configuration. They are also required to demonstrate behavior consistent with the defined SuperSpeed Device States.
All devices are assigned a USB address when enumerated by the host. Each device supports one or more pipes though which the host may communicate with the device.
All devices must be support a designed pipe at endpoint zero to which the device’s Default Control Pipe is attached. All devises support a common access mechanism for accessing information through this control pipe.
The USB 3.0 supports an increased power supply for the devices operating at the SuperSpeed. USB 3.0 devices within a single physical package (ie, a single peripheral) can consist of a number of functional topologies including single function , multiple functions on a single peripheral device (composite device), and permanently attached peripheral devices behind an integrated hub.
Architecture of USB 3.0APPLICATIONSThe USB ports are used for a number of applications. The USB ports get the popularity because of its simplicity as well the easiness in use. The main application of USB 3.0 is listed below.
1. USB 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 flash drives. This generality is because many systems can be controlled with the familiar idiom of file manipulation within directories (The process of making a novel device look like a familiar device is also known as extension)
2. USB 3.0 can also support portable hard disk drives. The earlier versions of USBs were not supporting the 3.5 inch hard disk drives. Originally conceived and still used today for optical storage devices (CD-RW drives, DVD drives, etc.), a number of manufacturers offer external portable USB hard drives, or empty enclosures for drives, that offer performance comparable to internal drives.
3. These external drives usually contain a translating device that interfaces a drive of conventional technology (IDE, ATA, SATA, ATAPI, or even SCSI) to a USB port. Functionally, the drive appears to the user just like an internal drive.
4. These are used to provide power for low power consuming devises. These can be used for charging the mobile phones.
5. 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 ATA (IDE), Serial ATA (SATA), and SCSI fulfill that role. However, USB has one important advantage in that it is possible to install and remove devices without opening the computer case, making it useful for external drives.
6. Mice and keyboards are frequently fitted with USB connectors, but because most PC motherboards still retain PS/2 connectors for the keyboard and mouse as of 2007, they are often supplied with a small USB-to-PS/2 adaptor, allowing usage with either USB or PS/2 interface.
7. Joysticks, keypads, tablets and other human-interface devices are also progressively migrating from MIDI, PC game port, and PS/2 connectors to USB.
8. It can also support Ethernet adapter, modem, serial port adapter etc
9. It can support Full speed hub, hi-speed hub, and SuperSpeed hub.
10. It can support USB smart card reader, USB compliance testing devices, Wi-Fi adapter, Bluetooth adapter, ActiveSync device, Force feedback joystick
CONCLUSION USB 3.0 is the next major revision of the ubiquitous Universal Serial Bus, created in 1996 by a consortium of companies led by Intel to dramatically simplify the connection between host computer and peripheral devices. Fast forwarding to 2009, USB 2.0 has been firmly entrenched as the de-facto interface standard in the PC world for years (with about 6 billion devices sold), and yet still the need for more speed by ever faster computing hardware and ever greater bandwidth demands again drive us to where a couple of hundred megabits per second is just not fast enough.
The Universal serial bus 3.0 is supporting a speed of about 5 Gb/sec ie ten times faster than the 2.0 version. And it is also faster than the new Firewire product S3200. So hopefully by the help of this SuperSpeed data transfer rate the USB 3.0 will be replacing many of the connecters in the future. The prototype of the USB 3.0 was already implemented by ASUSE in their motherboard. The drivers for the USB 3.0 are made available to the opensource Linux. The Linux kernel will support USB 3.0 with version 2.6.31, which will be released around August. Because of the backward compatibility of the USB 3.0 the devises which we are using now and the ports we are using now(which is USB 2.0) will be working proper with the new USB 3.0 devises and ports. 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.
In a nutshell, USB 3.0 promises the following:
• Higher transfer rates (up to 4.8Gbps)
• Increased maximum bus power and increased device current draw to better accommodate power-hungry devices
• New power management features
• Full-duplex data transfers and support for new transfer types
• New connectors and cables for higher speed data transfer...although they are backwards compatible with USB 2.0 devices and computers
REFERENCES1. USB 3.0 specifications released by USB consortium
2. http://www.reghardware.co.uk/superspeed_usb_3_guide
3. http://en.wikipedia.org/wiki/Universal_Serial_bus
4. http://www.usb.org/developers/ssusb
5. http://www.usb.org/developers/docs
6. http://www.wired.com/gadgetlab/2008/11/superspeed-us-1
7. http://tech.blorge.com
8. http://www.interfacebus.com
9. http://www.everythingusb.com/superspeed-usb.html
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