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1、USB3.01Introduction1.1MotivationTheoriginalmotivationfortheUniversalSerialBus(USB)camefromseveralconsiderations,twoofthemostimportantbeing:•Ease-of-useThelackofflexibilityinreconfiguringthePChadbeenacknowledgedastheAchilles’heeltoitsfurtherdeployment.Thecombinationofu
2、ser-friendlygraphicalinterfacesandthehardwareandsoftwaremechanismsassociatedwithnew-generationbusarchitectureshavemadecomputerslessconfrontationalandeasiertoreconfigure.However,fromtheenduser’spointofview,thePC’sI/Ointerfaces,suchasserial/parallelports,keyboard/mouse/
3、joystickinterfaces,etc.,didnothavetheattributesofplug-and-play.•PortExpansionTheadditionofexternalperipheralscontinuedtobeconstrainedbyportavailability.Thelackofabidirectional,low-cost,low-to-midspeedperipheralbusheldbackthecreativeproliferationofperipheralssuchasstor
4、agedevices,answeringmachines,scanners,PDA’s,keyboards,andmice.Existinginterconnectswereoptimizedforoneortwopointproducts.AseachnewfunctionorcapabilitywasaddedtothePC,anewinterfacehadbeendefinedtoaddressthisneed.Initially,USBprovidedtwospeeds(12Mb/sand1.5Mb/s)thatperip
5、heralscoulduse.AsPCsbecameincreasinglypowerfulandabletoprocesslargeramountsofdata,usersneededtogetmoreandmoredataintoandoutoftheirPCs.ThisledtothedefinitionoftheUSB2.0specificationin2000toprovideathirdtransferrateof480Mb/swhileretainingbackwardcompatibility.In2005,wit
6、hwirelesstechnologiesbecomingmoreandmorecapable,WirelessUSBwasintroducedtoprovideanewcablefreecapabilitytoUSB.USBisthemostsuccessfulPCperipheralinterconnecteverdefinedandithasmigratedheavilyintotheCEandMobilesegments.In2006aloneover2billionUSBdeviceswereshippedandther
7、eareover6billionUSBproductsintheinstalledbasetoday.Endusers“know”whatUSBis.Productdevelopersunderstandtheinfrastructureandinterfacesnecessarytobuildasuccessfulproduct.USBhasgonebeyondjustbeingawaytoconnectperipheralstoPCs.PrintersuseUSBtointerfacedirectlytocameras.PDA
8、suseUSBconnectedkeyboardsandmice.TheUSBOn-The-Godefinitionprovidesawayfortwodualrolecapabledevicestobeconnectedandnegotiatew