rollease acmeda RS485 User manual
ROLLEASEACMEDA
RS485NetworkCablingStandard
August2017
CONTENTS
August2017
Section1–RS485BUSOVERVIEW 3
Section2–NETWORKTOPOLOGIES 4
Section3–DIMENSIONALLIMITATIONS 5
Section4–CABLETYPES 7
Section5–PINOUTDEFINITION 8
Section6–GROUNDCONNECTIONSTRATEGY 10
Section7–INSTALLATIONOPTIONS 12
DISCLAIMER
INTRODUCTION
ThisproductspecificationsmanualhasbeenproducedbyRolleaseAcmedatosupplythenecessaryinformationforsafeandcorrectassemblyandinstallationofthissystem.
DISCLAIMER
RolleaseAcmedahasusedreasonablecareinpreparingtheinformationincludedinthisdocument,butmakesnorepresentationsorwarrantiesastothecompletenessoraccuracyoftheinformation.Informationissuppliedupontheconditionthatthepersonsreceiving
theinformationwillmaketheirowndeterminationastoitssuitabilityfortheirpurposespriortouse.RolleaseAcmedaassumesnoliabilitywhatsoeverforanydamagesincurredbyyouresultingfromerrorsinoromissionsfromtheinformationincludedherein.Rollease
Acmedareservestherighttomakechangeswithoutfurthernoticetoanyproductstoimprovereliability,functionordesign.
COPYRIGHT
COPYRIGHT©ROLLEASEACMEDA2017
Allrightsreserved.Nopartofthisdocumentmaybereproducedorutilisedinanymeans,byanymeans,electronicormechanicalincludingphotocopying,recordings,orbyanyinformationstorageorretrievalsystem,withouttheexpresspermissionfromRolleaseAcmed
SECTIONNO.DESCRIPTIONPAGENO.
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SECTION1 –RS485BUSOVERVIEW
Inordertoprovidereliable/robustcommunicationswithRolleaseAcmedaRS485‐enabledproducts,severalrecommendationsmustbecarefullyfollowed.Eachof
thesearelistedbelowandarecoveredindetailwithinthefollowingchapters.
1. NetworkTopologies–howtoconnecthubstotheRS485bus.
2. DimensionalLimitations–thedistancesthattheRS485buscanreliablycommunicateover.S
3. CableTypes–typesofcablesthatcanbeused.
4. GroundConnectionStrategy–how/whygroundingisrequired.
5. InstallationOptions–simpleplug&playorcustomizedoptions.
Diagram1.CompleteRS485network
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SECTION2 –NETWORKTOPOLOGIES
Beforeaninstallationcanbegin,itisimportanttounderstandhowtoconnectRolleaseAcmedahubstotheRS485bus.Thefollowingdiagramdepictsseveralcommon
networklayouts,butnotethatonlytwoareusableforaRS485bus.
Diagram2.RS485networktopologies
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SECTION3 –DIMENSIONALLIMITATIONS
ThemaximumlengthoftheRS485bus(includingstubslength)shouldnotexceed1000m(3281ft).Distancesgreaterthanthatwillresultinunreliable/error‐prone
communicationsandthereforeshouldbeavoided.Conversely,thedistancebetweennodesshouldbegreaterthan30cm(≈12in).
(a) TypicalResidential/LightcommercialInstallations(<100m)
Formostresidentialenvironmentswherethetotalbuslength(includingstubs)islessthan100m(328ft)theterminationresistorsarenotrequired.
Diagram3.Dimensionallimitations‐typicalresidential/lightcommercialinstallations
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(b) Longdistance/CommercialInstallations(<1000m)
Forlongerdistancecommunications,theterminationresistorsRT=120Ω(RApartno.MT02‐0401‐000005)mustbefittedtotheextremeendsofthebus.
Diagram4.Dimensionallimitations‐longdistance/commercialinstallations
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SECTION4 –CABLETYPES
RolleaseAcmedaonlyrecommendtheuseofTwistedPairethernetcables,thesecanbeeitherCAT5orCAT6.Formostresidentialenvironments,thecablecanbeof
eitherUTPorSTPtype.However,forlongdistanceorcommercialenvironmentsweonlyrecommendtheuseofSTPtypecables.
Picture1.Recommendedcables
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SECTION5 –PINOUTDEFINITION
EitherTIA/EIA568Aor568Bconfigurationcable(oracombinationofboth)canbeconnectedinaRARS485network.Thisisbecauseonlythecoresthatsharethesame
pinout&color‐codeacrossbothstandardsareused(seeinTable1.PinoutdefinitionandDiagram5.ColorcoresofcableconnectedinRS485network).
*Note:unusedcoresshouldbetiedtogroundiftheRS485busisgreaterthan100m.Refertopage15fordetails.
Table1.Pinoutdefinition
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Diagram5.ColorcoresofcableconnectedinRS485network
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SECTION6 –GROUNDCONNECTIONSTRATEGY
Whileadifferentialsignaldoesnotrequireasignalgroundtocommunicate,thegroundwireservesanimportantpurpose.Overadistanceofhundredsorthousandsof
feettherecanbeverysignificantdifferencesinthevoltagelevelof"ground."RS‐485networkscantypicallymaintaincorrectdatawithadifferenceof‐7to+12Volts.If
thegroundsdiffermorethanthatamount,datawillbelostandoftentheportitselfwillbedamaged.Thefunctionofthesignalgroundwireistotiethesignalground
ofeachofthenodestoonecommonground.
Strategy(a):ShieldingAgainstLowFrequencyNoise
Formostresidentialorlightcommercialenvironments,oneendoftheshieldshouldbeconnectedtogroundinordertoimproveshieldingagainstlowfrequency
electricalnoisesuchas50/60Hzmainsnoise.(refertoDiagram5)
Diagram6.Groundconnection‐shieldingagainstlowfrequencynoise
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Strategy(b):ShieldingAgainstHighFrequencyNoise
Forindustrial/electricalnoisyenvironments,bothendsoftheshieldshouldbeconnectedtogroundinordertoimproveshieldingagainsthighfrequencyelectrical
noisesuchasswitch‐modepowersuppliesetc.(refertoDiagram6)
Diagram7.Groundconnection‐shieldingagainsthighfrequencynoise
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SECTION7 –INSTALLATIONOPTIONS
(a)“Plug&Play”cablingOption
Pre‐terminatedethernetcable(commonlyavailablefrommostelectricalstores)canbeusedtocreatearobustRS485networkwithouttheneedforspecialized
terminationskills&tools.RolleaseAcmedaprovideRJ45‐compatibleconnectors/splitters(RApartno.MT02‐0401‐000004)forthistypeofinstallation.
Diagram8.Option(a)“Plug&Play”cabling
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(b)Hard‐wiredcablingOption
Unterminatedethernetcable(commonlyavailablefrommostelectricalstores)canbeusedtocreatea“customized/cut‐to‐length”RS485networkwithouttheneedfor
specializedterminationskills&tools.RolleaseAcmedaprovideaterminal‐block‐typeadapter(RApartno.MT02‐0401‐000006)allowingthecabletobeeasily
joined/split.
Diagram9.Option(b)Hard‐wiredcabling
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(c)UnusedCablePairs
i.Residential
Formostresidentialorlightcommercialenvironmentswherethebusis<100m,theunusedwiresshouldbeconnectedtoground.
Diagram10.UnusedCablePairsconnection–Residential
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ii.Longdistance/commercial
Whenusingethernetcableforsinglepairapplications,theunusedwiresshouldbeproperlyterminatedtogroundwithRG=100Ωatbothcableends.This
preventsnoisecouplingduetoself‐resonanceatallsortsoffrequenciesfromtheunusedwiresintothedatapair.
Diagram11.UnusedCablePairsconnection–Longdistance/commercial
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(d)Biasresistor
InRS485networkwheninputsarebetween‐200mVand+200mV,receiveroutputis"undefined".Therearefourcommonfaultconditionsthatresultintheundefined
receiveroutputthatcancauseerroneousdata:
1)Alltransmittersinasystemareinshutdown.
2)Thereceiverisnotconnectedtothecable.
3)Thecableisopencircuit.
4)Thecableisshortcircuit.
Thebiasresistors(510Ω/1W)areconnectedtoVCC(DC5V)andsignalgroundtosolvethisissue(refertoDiagram8).Thiswaythebuswillalwaysbeataknownlevel
regardlessofthefaultcondition.AllRAPulsehubshavetheseresistorsinternally,sotheonlybenefitofaddingtheseexternallyisifthefirsthub’sconnectionbecomes
faultythebuswillstillbeat“knownlevels”forthemaster/controller.
Diagram12.Optionalbiasresistorinstallation
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