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TypicalApplication
CANH
CANL
TMS320F243
SN65HVD251
D R
CANTX CANRX
TMS320F243
SN65HVD251
D R
地
CANTX CANRX
TMS320LF2407A
SN65HVD230
D R
CANTX CANRX
5 v
地
5 v
地
3.3 v
stub 线条 –– 0.3 m 最大值
总线 线条 – 40 m 最大值
120
V
ref
R
S
0.1
F
V
CC
V
ref
R
S
V
CC
V
ref
R
S
0.1
F 0.1
F
V
CC
120
传感器, actuator, 或者
控制 设备
传感器, actuator, 或者
控制 设备
传感器, actuator, 或者
控制 设备
SN65HVD251
SLLS545B–NOVEMBER2002–REVISEDSEPTEMBER2003
aneyepatternisausefultoolformeasuringoverallsignalquality.asdisplayedinfigure24,thedifferential
signalchangeslogicstatesintwoplacesonthedisplay,producingan
eye
.insteadofviewingonlyonelogic
crossingonthescope,anentire
位
ofdataisbroughtintoview.theresultingeyepatternincludesallofthe
effectsofsystemicandrandomdistortion,anddisplaysthetimeduringwhichasignalmaybeconsideredvalid.
Theheightoftheeyeaboveorbelowthereceiverthresholdvoltagelevelatthesamplingpointisthenoise
marginofthesystem.jitteristypicallymeasuredatthedifferentialvoltagezero-crossingduringthelogicstate
transitionofasignal.notethatjitterpresentatthereceiverthresholdvoltagelevelisconsideredbysometobea
moreeffectiverepresentationofthejitterattheinputofareceiver.
asthesumofskewandnoiseincreases,theeyeclosesanddataiscorrupted.closingthewidthdecreasesthe
timeavailableforaccuratesampling,andloweringtheheightentersthe900mvor500mvthresholdofa
接受者.
differentsourcesinducenoiseontoasignal.themoreobviousnoisesourcesarethecomponentsofa
transmissioncircuitthemselves;thesignaltransmitter,查出&放大;cables,连接器,andthereceiver.在之外
那,thereisaterminationdependency,交叉-talkfromclocktracesandotherproximityeffects,vcc&放大;地面
bounce,andelectromagneticinterferencefromnear-byelectricalequipment.
thebalancedreceiverinputsofthehvd251mitigatemostallsourcesofsignalcorruption,andwhenusedwitha
qualityshieldedtwisted-paircable,helpinsuredataintegrity.
figure25.typicalhvd251application
16
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