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1、USB3.01Introduction1.1MotivationTheoriginalmotivationfortheUniversalSerialBus(USB)camefromseveralconsiderations,twoofthemostimportantbeing:•Ease-of-useThelackofflexibilityinreconfiguringthePChadbeenacknowledgedastheAchilles’heeltoitsfurtherdeployment.Thecombinationo
2、fuser-friendlygraphicalinterfacesandthehardwareandsoftwaremechanismsassociatedwithnew-generationbusarchitectureshavemadecomputerslessconfrontationalandeasiertoreconfigure.However,fromtheenduser’spointofview,thePC’sI/Ointerfaces,suchasserial/parallelports,keyboard/mo
3、use/joystickinterfaces,etc.,didnothavetheattributesofplug-and-play.•PortExpansionTheadditionofexternalperipheralscontinuedtobeconstrainedbyportavailability.Thelackofabidirectional,low-cost,low-to-midspeedperipheralbusheldbackthecreativeproliferationofperipheralssuch
4、asstoragedevices,answeringmachines,scanners,PDA’s,keyboards,andmice.Existinginterconnectswereoptimizedforoneortwopointproducts.AseachnewfunctionorcapabilitywasaddedtothePC,anewinterfacehadbeendefinedtoaddressthisneed.Initially,USBprovidedtwospeeds(12Mb/sand1.5Mb/s)t
5、hatperipheralscoulduse.AsPCsbecameincreasinglypowerfulandabletoprocesslargeramountsofdata,usersneededtogetmoreandmoredataintoandoutoftheirPCs.ThisledtothedefinitionoftheUSB2.0specificationin2000toprovideathirdtransferrateof480Mb/swhileretainingbackwardcompatibility.
6、In2005,withwirelesstechnologiesbecomingmoreandmorecapable,WirelessUSBwasintroducedtoprovideanewcablefreecapabilitytoUSB.USBisthemostsuccessfulPCperipheralinterconnecteverdefinedandithasmigratedheavilyintotheCEandMobilesegments.In2006aloneover2billionUSBdevicesweresh
7、ippedandthereareover6billionUSBproductsintheinstalledbasetoday.Endusers“know”whatUSBis.Productdevelopersunderstandtheinfrastructureandinterfacesnecessarytobuildasuccessfulproduct.USBhasgonebeyondjustbeingawaytoconnectperipheralstoPCs.PrintersuseUSBtointerfacedirectl
8、ytocameras.PDAsuseUSBconnectedkeyboardsandmice.TheUSBOn-The-Godefinitionprovidesawayfortwodualrolecapabledevicestobeconnectedandnegotiatew
