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Rev 3.0B Feb.08 68
8
8: Configuring Modbus/BSAP
• Configuring the Raven
at the Polling Host
for Modbus on UDP
• Configuring the
Remote Ravens for
Modbus with UDP
TheRavensupportsModbusASCII,ModbusRTU,BSAP,and
canalsoemulateotherprotocolslikeDF1orothersusingits
ModbusVariablefeature.
Modbus Overview
TheModbusProtocol,developedbyModiconin1979,
providesforclient‐server(alsoreferredtoasmaster‐slave)
communicationsbetweenintelligentdevices.Asadefacto
standard,itisthemostwidelyusednetworkprotocolinthe
industrialmanufacturingenvironmenttotransferdiscrete/
analogI/Oandregisterdatabetweencontroldevices.
Modbus,
BSAP,andotherModbusvariationsareoftenusedin
conjunctionwithtelemetrydevices.
Tip: This section is just a brief overview of Modbus. For more infor-
mation, refer to your Modbus equipment distributor or manufacturer or
http://www.modbus.org.
Te l e me tr y
Telemetryisanautomatedcommunicationsprocessbywhich
dataiscollectedfrominstrumentslocatedatremoteorinacces
‐
siblepointsandtransmittedtoreceivingequipmentfor
measurement,monitoring,display,andrecording.Trans
‐
missionoftheinformationmaybeoverphysicalpairsofwires,
telecommunicationcircuits,radiosorsatellite.
Remote Terminal Unit (RTU)
Modbuswasoriginallydesignedtobeusedinaradio
environmentwherepacketsarebroadcastfromacentral
station(alsocalledmasterorhost)toagroupofremoteunits.
Eachremoteunit,RemoteTerminalUnit(RTU),hasa
hexidecimalidentificationnumber(ID).Thefirstpartof the
broadcastpacketcontains
anRTUIDwhichcorrespondstothe
IDofoneoftheremoteunits.TheModbushostlooksforthe
IDandsendstoonlytheunitwiththematchingID.TheRTU
wouldthenreplybacktothecentralstation.