USB协会标准

USB2.0SpecificationEngineeringChangeNotice(ECN)#1:Mini-BconnectorDate:10/20/2000ReasonforECN:TheUSB2.0specifieddevice-sideconnector–theBconnector–istoolargeforusewithanewgenerationofhandheldandmobiledevices,e.g.,cellphoneswhichwouldbenefitfromconnectivitytothePC.ThisECNincorporatesaspecificationofadevice-sideminiconnector(hereafterreferredtoasamini-Bconnector).Thenewconnectoronlyappliestoupstreamfacingports,i.e.,connectorsondevices.SummaryofECN:ThebulkoftheECNspecifiesthemechanicalrequirementsforthemini-Bplug,receptacleandcableassembly.Italsoidentifiestheusagescopeofthisconnector.ThelastpartoftheECNdescribestheminimumtestcriteriaandperformancerequirementsforthenewconnector.BenefitsofECN:TheECNenablesstandardizationofminiaturedevice-sideUSBconnectorsandconsequenteconomiesofscalesandlowercostforanewandgrowingclassofdeviceswhichwillbenefitfromconnectivitytothePC.ThestandardizationalsoallowsleveragingofthecompliancetestandcertificationmodelwhichisalreadyinplaceforUSBconnectors.AssessmentofImpactonCurrentSpecificationandCurrentUSBProducts:TheconnectorspecifiedintheECNwillnothaveanyimpactonhardwareorsoftwareofexistingUSBproducts.ThecurrentUSBspecalreadyallowsforvendor-specificdevicesideconnectors–suchcableassembliesarecalledcaptiveassemblies.AllthattheECNdoesistoidentifyonesuchconnectorforuseindeviceswhichneedthesmallersizeofconnector.Thereisapotentialforsomeend-userconfusionbecauseoftwostandardcableoptions;butthiscanbemitigatedbyappropriateend-usereducation.StructureofECN:TheECNisintheformofanewChapter6withthemini-Bconnectorrequirementsinsertedintotheappropriatelocations.Thisformatenablesspecificationofthenewconnectorincontext.UniversalSerialBusSpecificationRevision2.085Chapter6MechanicalThischapterprovidesthemechanicalandelectricalspecificationsforthecables,connectors,andcableassembliesusedtointerconnectUSBdevices.Thespecificationincludesthedimensions,materials,electrical,andreliabilityrequirements.ThischapterdocumentsminimumrequirementsfortheexternalUSBinterconnect.Substitutematerialmaybeusedaslongasitmeetstheseminimums.6.1ArchitecturalOverviewTheUSBphysicaltopologyconsistsofconnectingthedownstreamhubporttotheupstreamportofanotherhubortoadevice.TheUSBcanoperateatthreespeeds.High-speed(480Mb/s)andfull-speed(12Mb/s)requiretheuseofashieldedcablewithtwopowerconductorsandtwistedpairsignalconductors.Low-speed(1.5Mb/s)recommends,butdoesnotrequiretheuseofacablewithtwistedpairsignalconductors.Theconnectorsaredesignedtobehotplugged.TheUSBIconontheplugsprovidestactilefeedbackmakingiteasytoobtainproperorientation.6.2KeyedConnectorProtocolTominimizeenduserterminationproblems,USBusesa“keyedconnector”protocol.ThephysicaldifferenceintheSeries“A”and“B”(or“mini-B”)connectorsinsuresproperenduserconnectivity.The“A”connectoristheprinciplemeansofconnectingUSBdevicesdirectlytoahostortothedownstreamportofahub.AllUSBdevicesmusthavethestandardSeries“A”connectorspecifiedinthischapter.The“B”(or“mini-B”)“B”connectorallowsdevicevendorstoprovideastandarddetachablecable.Thisfacilitatesendusercablereplacement.Figure6-1Figure6-1illustratesthekeyedconnectorprotocol.UniversalSerialBusSpecificationRevision2.086SeriesAConnectorsSeriesBConnectors♦SeriesAplugsarealwaysorientedupstreamtowardstheHostSystem♦SeriesBplugsarealwaysorienteddownstreamtowardstheUSBDeviceAPlugs(FromtheUSBDevice)BPlugs(FromtheHostSystem)BReceptacles(UpstreamInputtotheUSBDeviceorHub)AReceptacles(DownstreamOutputfromtheUSBHostorHub)Seriesmini-BConnectors♦Seriesmini-BplugsarealwaysorienteddownstreamtowardstheUSBDevicemini-BPlugs(FromtheHostSystem)mini-BReceptacles(UpstreamInputtotheUSBDeviceorHub)Figure6-1.KeyedConnectorProtocolUniversalSerialBusSpecificationRevision2.087Thefollowinglistexplainshowtheplugsandreceptaclescanbemated:•Series“A”receptaclemateswithaSeries“A”plug.Electrically,Series“A”receptaclesfunctionasoutputsfromhostsystemsand/orhubs.•Series“A”plugmateswithaSeries“A”receptacle.TheSeries“A”plugalwaysisorientedtowardsthehostsystem.•Series“B”receptaclemateswithaSeries“B”plug(male).Electrically,Series“B”receptaclesfunctionasinputstohubsordevices.•Series“B”plugmateswithaSeries“B”receptacle.TheSeries“B”plugisalwaysorientedtowardstheUSBhubordevice.•Series“mini-B”receptaclemateswithaSeries“mini-B”plug(male).Electrically,Series“mini-B”receptaclesfunctionasinputstohubsordevices.•Series“mini-B”plugmateswithaSeries“mini-B”receptacle.TheSeries“mini-B”plugisalwaysorientedtowardstheUSBhubordevice.6.3CableUSBcableconsistsoffourconductors,twopowerconductors,andtwosignalconductors.High-/full-speedcableconsistsofasignalingtwistedpair,VBUS,GND,andanoverallshield.High-/full-speedcablemustbemarkedtoindicatesuitabilityforUSBusage(seeSection6.6.2).High-/full-speedcablemaybeusedwitheitherlow-speed,full-speed,orhigh-speeddevices.Whenhigh-/full-speedcableisusedwithlow-speeddevices,thecablemustmeetalllow-speedrequirements.Low-speedrecommends,butdoesnotrequiretheuseofacablewithtwistedsignalingconductors.6.4CableAssemblyThisspecificationdescribesthreeUSBcableassemblies:standarddetachablecable,hi