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usb (753), the (617), and (354), from (162), for (145), device (132), retrieved (125), #devices (115), with (112), original (111), archived (106), power (100), specification (83), pdf (80), may (76), host (75), data (71), that (68), type (65), bus (65), usb4 (62), are (62), gbit (62), gen (61), edit (56), interface (55), can (53), standard (52), speed (49), serial (44), 2018 (43), implementers (42), forum (42), superspeed (42), september (40), audio (40), computer (39), 2021 (39), this (38), connectors (38), not (38), was (36), cable (36), high (36), all (35), class (35), use (34), thunderbolt (34), protocol (34), april (34), june (33), used (32), 2023 (31), universal (31), which (31), transfer (31), 2022 (30), july (30), other (30), connector (30), two (30), november (29), cables (29), 2014 (29), one (29), low (29), full (29), august (28), mode (28), firewire (27), october (26), march (26), also (26), peripheral (25), ports (25), 2017 (25), has (25), support (25), such (25), over 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through its single type b receptacle or a captive cable with a type a plug a hub may connect to the host either directly or through one or more additional hubs prior to type c usb on the go allowed a device such as a smartphone to take either the host or the peripheral device role with a single type ab receptacle micro ab superseded in 2014 or mini ab deprecated 2007 97 that accepted both type a and type b plugs usb connector types multiplied as the specification progressed the original usb specification detailed standard a and standard b plugs and receptacles these were originally referred to as simply type a and type b they were renamed standard out of necessity to distinguish from mini and later micro connectors the data contacts in the standard plugs are recessed compared to the power and ground contacts so that devices are safely electrically connected before the more delicate data communications circuitry is connected preventing damage some devices operate in different modes depending on whether the data connection is made simple power sources do not include data connections instead shorting the data contacts together but allow any capable usb device to charge or operate through a standard usb cable charging cables provide power connections but not data though the standard requires at least a usb 2 0 data connection capability in a non standard charge only cable the data wires are shorted at the device end otherwise the device may reject the charger as unsuitable cabling edit main article usb hardware cabling a variety of usb cables for sale in hong kong the usb 1 1 standard specifies that a standard cable can have a maximum length of 5 meters 16 ft 5 in with devices operating at full speed 12 mbit s and a maximum length of 3 meters 9 ft 10 in with devices operating at low speed 1 5 mbit s 98 99 100 usb 2 0 provides for a maximum cable length of 5 meters 16 ft 5 in for devices running at high speed 480 mbit s 100 the usb 3 0 standard does not directly specify a maximum cable length requiring only that all cables meet an electrical specification for copper cabling with awg 26 wires the maximum practical length is 3 meters 9 ft 10 in 101 usb bridge cables edit two computers hosts can easily be connected through a usb c cable but before type c hosts could not be connected to each other with common usb cables usb bridge cables or data transfer cables can be found within the market offering direct pc to pc connections a bridge cable is actually an electronic device that appears as a usb peripheral device to each of the connected hosts allowing peer to peer communication between the computers such usb bridge cables are used to transfer files between two computers via their usb ports popularized by microsoft as windows easy transfer the microsoft utility used a special usb bridge cable to transfer personal files and settings from a computer running an earlier version of windows to a computer running a newer version in the context of the use of windows easy transfer software the bridge cable can sometimes be referenced as easy transfer cable many usb bridge data transfer cables are still usb 2 0 but there are also a number of usb 3 0 transfer cables despite usb 3 0 being ten times as fast as usb 2 0 usb 3 0 transfer cables are only two to three times as fast given their design clarification needed the usb 3 0 specification introduced an a to a cross over cable without power for connecting two pcs these are not meant for data transfer but are aimed at diagnostic uses dual role usb connections edit usb bridge cables have become less important with usb dual role device capabilities introduced with the usb 3 1 specification under the most recent specifications usb supports most scenarios connecting systems directly with a type c cable for the capability to work however connected systems must support role switching dual role capability requires there be two controllers within the system as well as a role controller while this can be expected in a mobile platform such as a tablet or a phone desktop pcs and laptops often do not support dual roles 102 power edit main article usb hardware power usb host and hub recepticles supply power at a nominal 5 v dc via the v_bus pin to upstreaming usb devices low power and high power devices edit this section describes the power distribution model of usb that existed before usb power delivery usb pd on devices that do not use bc or pd usb provides up to 4 5 w through type a and type b connectors and up to 15 w through usb c all pre pd usb power is provided at 5 v for a host providing power to devices usb has a concept of the unit load any device may draw power of one unit and devices may request more power in these discrete steps it is not required that the host provide requested power and a device may not draw more power than negotiated low power devices can draw no more than one unit all devices must act as low power devices when starting out as unconfigured for usb devices up to usb 2 0 a unit load is 100 ma or 500 mw while usb 3 0 defines a unit load as 150 ma 750 mw full featured usb c can support low power devices with a unit load of 250 ma or 1250 mw high power devices e g typical 2 5 inch hard disk drives can draw more than one unit usb up to 2 0 allows a host or hub to provide up to 2 5 w to each device in five discrete steps of 100 ma and superspeed devices usb 3 x allows a host or a hub to provide up to 4 5 w in six steps of 150 ma usb c allows for dual lane operation of usb 3 x with larger unit load 250 ma up to 7 5 w 103 usb c also allows for type c current as a replacement for usb bc signaling power availability in a simple way without needing any data connection 104 usb power standards specification max current voltage max power low power device up to usb 2 0 100 ma 5 v a 0 50 w low power superspeed usb 3 x device 150 ma 5 v a 0 75 w high power device up to usb 2 0 500 ma b 5 v 2 5 w high power superspeed usb 3 x single lane device 900 ma c 5 v 4 5 w high power superspeed usb 3 x dual lane device d 1 5 a e 5 v 7 5 w battery charging bc 1 5 a 5 v 7 5 w type c 1 5 a 3 a 5 v 7 5 w 15 w power delivery spr d 5 a f up to 20 v 100 w power delivery epr d 5 a f up to 48 v g 240 w 1 2 the v bus supply from a low powered hub port may drop to 4 40 v up to five unit loads with non superspeed devices one unit load is 100 ma up to six unit loads with superspeed devices one unit load is 150 ma 1 2 3 for usb c only up to six unit loads with multi lane devices one unit load is 250 ma 1 2 3 a 60 w operation requires an electronically marked cable rated at 5 a 20 v 100 w operation requires an electronically marked extended power range epr cable to recognize battery charging mode a dedicated charging port places a resistance not exceeding 200 ω across the d and d terminals shorted or near shorted data lanes with less than 200 ω of resistance across the d and d terminals signify a dedicated charging port dcp with indefinite charging rates 105 106 in addition to standard usb there is a proprietary high powered system known as poweredusb developed in the 1990s and mainly used in point of sale terminals such as cash registers signaling edit main article usb communications signaling usb phy usb signals are transmitted using differential signaling on twisted pair data wires with 90 ω 15 characteristic impedance 107 usb 2 0 and earlier specifications define a single pair in half duplex hdx usb 3 0 and later specifications define one dedicated pair for usb 2 0 compatibility and two or four pairs for data transfer two data wire pairs realising full duplex fdx for single lane 1 variants require at least superspeed ss connectors four pairs realising full duplex for two lane 2 variants require usb c connectors usb4 gen 4 requires the use of all four pairs but allow for asymmetrical pairs configuration 108 in this case one data wire pair is used for the upstream data and the other three for the downstream data or vice versa usb4 gen 4 use pulse amplitude modulation on three levels providing a trit of information every baud transmitted the transmission frequency of 12 8 ghz translate to a transmission rate of 25 6 gbd 109 and the 11 bit to 7 trit translation provides a theoretical maximum transmission speed just over 40 2 gbit s 110 usb data operation modes operation mode name introduced in lanes encoding data wires nominal signaling rate original label usb if current 53 current old marketing name logo low speed n a usb 1 0 1 hdx nrzi 2 1 5 mbit s half duplex low speed usb ls basic speed usb full speed 12 mbit s half duplex full speed usb fs high speed usb 2 0 480 mbit s half duplex hi speed usb hs usb 3 2 gen 1 1 usb 3 0 usb 3 1 gen 1 usb 3 0 1 fdx 1 hdx a 8b 10b 6 5 gbit s symmetric superspeed usb ss usb 5gbps usb 3 2 gen 2 1 usb 3 1 gen 2 usb 3 1 128b 132b 10 gbit s symmetric superspeed ss usb 10gbps usb 3 2 gen 1 2 n a usb 3 2 2 fdx 1 hdx a 8b 10b 10 10 gbit s symmetric n a usb 3 2 gen 2 2 128b 132b 20 gbit s symmetric superspeed usb 20gbps usb 20gbps usb4 gen 2 1 usb4 1 fdx 1 hdx a 64b 66b b 6 used of 10 10 gbit s symmetric usb 10gbps usb4 gen 2 2 2 fdx 1 hdx a 10 20 gbit s symmetric usb 20gbps usb4 gen 3 1 1 fdx 1 hdx a 128b 132b b 6 used of 10 20 gbit s symmetric usb4 gen 3 2 2 fdx 1 hdx a 10 40 gbit s symmetric usb 40gbps usb4 gen 4 2 usb4 2 0 2 fdx 1 hdx a pam 3 11b 7 t 10 80 gbit s symmetric usb 80gbps asymmetric 1 hdx a 40 gbit s up 120 gbit s down n a 120 gbit s up 40 gbit s down 1 2 3 4 5 6 7 8 usb 2 0 implementation 1 2 usb4 can use optional reed solomon forward error correction rs fec in this mode 12 16 b 128 bit symbols are assembled together with 2 b 12 bit 4 bit reserved synchronization bits indicating the respective symbol types and 4 b of rs fec to allow to correct up to 1 b of errors anywhere in the total 198 b block low speed ls and full speed fs modes use a single data wire pair labeled d and d in half duplex transmitted signal levels are 0 0 0 3 v for logical low and 2 8 3 6 v for logical high level the signal lines are not terminated high speed hs uses the same wire pair but with different electrical conventions lower signal voltages of 10 to 10 mv for low and 360 to 440 mv for logical high level and termination of 45 ω to ground or 90 ω differential to match the data cable impedance superspeed ss adds two additional pairs of shielded twisted data wires and new mostly compatible expanded connectors besides another grounding wire these are dedicated to full duplex superspeed operation the superspeed link operates independently from the usb 2 0 channel and takes precedence on connection link configuration is performed using lfps low frequency periodic signaling approximately at 20 mhz frequency and electrical features include voltage de emphasis at the transmitter side and adaptive linear equalization on the receiver side to combat electrical losses in transmission lines and thus the link introduces the concept of link training superspeed ss uses a new coding scheme with an increased signaling rate gen 2 1 mode and or the additional lane of usb c gen 1 2 and gen 2 2 modes a usb connection is always between an a end a downstream facing port dfp of either a host or a hub and a b end the upstream facing port ufp of either a peripheral device or a hub historically this was made clear by the fact that hosts had only type a and peripheral devices had only type b ports and every compatible cable had one type a plug and one type b plug usb c type c is a single connector that replaces all legacy type a and type b connectors so when both sides are equipment with usb type c ports normally the device s type defines which is the dfp and which is the ufp some devices e g modern smart phones can act as both consequently the connected devices negotiate which is the host and which is the peripheral device protocol layer edit main article usb communications protocol layer during usb communication data is transmitted as 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 transactions edit main article usb communications transaction the basic transactions of usb are out transaction in transaction setup transaction control transfer exchange related standards edit the wireless usb logo media agnostic usb edit the usb implementers forum introduced the media agnostic usb ma usb v 1 0 wireless communication standard based on the usb protocol on 29 july 2015 wireless usb is a cable replacement technology and uses ultra wideband wireless technology for data rates of up to 480 mbit s 111 the usb if used wigig serial extension v1 2 specification as its initial foundation for the ma usb specification and is compliant with superspeed usb 3 0 and 3 1 and hi speed usb usb 2 0 devices that use ma usb will be branded as powered by ma usb provided the product qualifies its certification program 112 interchip usb edit main article interchip usb interchip usb is a chip to chip variant that eliminates the conventional transceivers found in normal usb the hsic physical layer uses about 50 less power and 75 less board area compared to usb 2 0 113 it is an alternative standard to spi and i2c usb c edit main article usb c usb c officially usb type c is a standard that defines a new connector and several new connection features among them it supports alternate mode which allows transporting other protocols via the usb c connector and cable this is commonly used to support the displayport or hdmi protocols which allows connecting a display such as a computer monitor or television set via usb c all other connectors are not capable of two lane operations gen 1 2 and gen 2 2 in usb 3 2 but can be used for one lane operations gen 1 1 and gen 2 1 114 displaylink edit main article displaylink displaylink is a technology which allows multiple displays to be connected to a computer via usb it was introduced around 2006 and before the advent of alternate mode over usb c it was the only way to connect displays via usb it is a proprietary technology not standardized by the usb implementers forum and typically requires a separate device driver on the computer comparisons with other connection methods edit firewire ieee 1394 edit at first usb was considered a complement to firewire ieee 1394 technology which was designed as a high bandwidth serial bus that efficiently interconnects peripherals such as disk drives audio interfaces and video equipment in the initial design usb operated at a far lower data rate and used less sophisticated hardware it was suitable for small peripherals such as keyboards and pointing devices the most significant technical differences between firewire and usb include usb networks use a tiered star topology while ieee 1394 networks use a tree topology usb 1 0 1 1 and 2 0 use a speak when spoken to protocol meaning that each peripheral communicates with the host when the host specifically re...
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