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H o m e > Drivers > M odbu s O PC Se rve r Su i t e M a t r ik onO PC O PC Se rve r s

Modbus OPC Server Suite MatrikonOPC OPC ServersHow to connect to Modbus devices using OPC

Of a ll the industrial protocols out there, Modbus is o ne of the mo st popular. Its openprotocol, easy imple mentation, and ba sic featureset all combine to mak e it a wellused protocol. This article will explain how to connect Modbus to OP C and thedifferences b etween basic communications a nd m ore advanced telemetrycommunication between Mod bus and O PC

Basic media options:Serial (either RS232 or RS485)Ethernet

More advanced connection options:Radio

GPRSSatellitedial up modem

ProtocolsModbusModbus RTUModbus on TCPEnron ModbusModbus PlusDaniel ModbusBently Nevada Modbus

Registers Data in Modbus is grouped in registers

0x: read/write tags that can be on or off. Some times called "coils", "digitals","relays", or "booleans" Address range from 00001-09999

1x: read-o nly tags that can be o n or off. Som etimes called "coils", "digitals", "relays", or "booleans " Address range from 10001-19999

3x: R ead only tags. 16 bit sizes by default. Also called input registers4x: R ead/write tags. 16 b it sizes by de fault. Also called ho lding registers.

Interpreting different registers Wh at if Im using floats, 32 bit "wide" registers, unsigned integer, swapped wordorder, ASCII strings, etc? With these registers, most OPC Servers offer letter suffixesor some other way of denoting that the O PC Server should treat that tag differently.With the Matrikon O PC Server for Modbus , as an ex amp le, a paired register for a 32bit floating-point real O PC Ta g m ight look like this: TestChannel.TestDevice.4:34P

Master/Slave Control Many peop le out there know that OP C Clients are typically embed ded in a pplicationsthat need to have control over communications. OPC Servers are typically built for

applications that do not need to control the comm unications. Many protocols outthere, such as Modbus, also follow this philosophy. Modbus is Master/Slave, just likeOPC is Client/Server. Usually, you want your OPC Server to act as the ModbusMaster, and relay the control down the line. But sometimes, youll want your device tohave more control over the communications such as if your device was to "phone

home " in an alarm condition. In these instances, youll need your OPC Server to actas a Mo dbus slave. Most OP C Servers do no t support slave mo de, so if you nee d it,be sure to a sk your vendor.

Telemetry The problem were going to run into with advanced connections is that OPC Serversare just passive translators. With a complex telemetry environment, where wecommunicate with many RTUs or PLCs over high latency, low bandwidth, sharedcommunication links; were going to need an O PC Server with more brains. These"brains" are m ore advanced timing and p olling options. A good Telemetry SCADA

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8/14/2019 OPC Modbus at MatrikonOPC

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erver s ou suppor roun ro n po ng, n errup eman po ng, an avemany a dvanced timing parameters to a ccount for different delays or polling times.

Multiple Masters One of the differences between the two is that you can have m ore than 1 OP C Clientconnected to each OPC Server, whereas you dont usually want 2 Modbus Masterstalking to the same Modbus slave. This can be a problem if youre using redundantOPC Servers or multiple Master applications. Be s ure to talk to your vendor onalleviating these issue s in your application if these are an issue.

For more information on Mo dbus, see Modbus-IDA at modbus.org

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