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APPLICATIONINFORMATION
500 mv 门槛
900 mv 门槛
准许能 jitter
噪音 余裕
噪音 余裕
接受者 发现 window
75% 样本 要点
SN65HVD251
SLLS545B–NOVEMBER2002–REVISEDSEPTEMBER2003
latorsinasystemalsoneedtobeaccountedforwith
Thebasicsofarbitrationrequirethatthereceiverat
adjustmentsinsignalingrateandstub&放大;buslength.
thesendingnodedesignatethefirstbitasdominant
Table2liststhemaximumsignalingratesachieved
orrecessiveaftertheinitialwaveofthefirstbitofa
withthesn65hvd251inhigh-speedmodewith
messagetravelstothemostremotenodeona
severalbuslengthsofcategory5,shieldedtwisted
networkandbackagain.典型地,这个
样本
是
一双(cat5stp)缆索.
madeat75%ofthebitwidth,andwithinthis
限制,themaximumallowablesignaldistortionin
table4.maximumsignalingratesforvarious
aCANnetworkisdeterminedbynetworkelectrical
CableLengths
参数.
buslength(m)signalingrate(kbps)
Factorstobeconsideredinnetworkdesigninclude
301000
这
≈
5ns/mpropagationdelayoftypicaltwisted-一双
100500
buscable;signalamplitudelossduetotheloss
250250
mechanismsofthecable;andthenumber,长度,
andspacingofdrop-线条(stubs)onanetwork.下面
500125
strictanalysis,variationsamongthedifferentoscil-
100062.5
theiso11898standardspecifiesamaximumbuslengthof40mandmaximumstublengthof0.3mwitha
maximumof30nodes.不管怎样,withcarefuldesign,userscanhavelongercables,longerstublengths,和
manymorenodesonabus.(便条:非-standardapplicationmaycomewithatrade-offinsignalingrate.)alarge
numberofnodesrequiresatransceiverwithhighinputimpedancesuchasthehvd251.
thestandardspecifiestheinterconnecttobeasingletwisted-paircable(shieldedorunshielded)with120
Ω
characteristicimpedance(zo).resistorsequaltothecharacteristicimpedanceofthelineterminatebothendsof
thecabletopreventsignalreflections.unterminateddrop-linesconnectnodestothebusandshouldbekeptas
shortaspossibletominimizesignalreflections.
连接器,whilenotspecifiedbythestandardshouldhaveaslittleeffectaspossibleonstandardoperating
parameterssuchascapacitiveloading.althoughunshieldedcableisusedinmanyapplications,数据
transmissioncircuitsemployingCANtransceiversareusuallyusedinapplicationsrequiringarugged
interconnectionwithawidecommon-modevoltagerange.因此,shieldedcableisrecommendedinthese
electronicallyharshenvironments,andwhencoupledwiththestandard's–2-vto7-vcommon-moderangeof
tolerablegroundnoise,helpstoensuredataintegrity.thehvd251enhancesthestandard'sinsuranceofdata
integritywithanextended–7-vto12-vrangeofcommon-modeoperation.
figure24.typicalcandifferentialsignaleye-模式
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