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6.3
Alternative communications methods
6.3.1
Modbus TCP (Ethernet)
Modbus TCP is a version of Modbus for use over Ethernet networks. Except for the communication between
devices it operates in a similar way to Modbus RTU (in that devices have documented memory maps that
you can use to access and interpret data).
Modbus RS485 can be converted to Modbus TCP by using a suitable Modbus Gateway like the SL-MODGW. This can greatly simplify cabling, especially if you already require Ethernet to that location. It also allows
you to connect distant parts of the network using a single fibre-optic link.
Media converters can be used to convert between Copper and Fibre-Optic Ethernet networks.
Copper Ethernet Links
Copper Ethernet is the most commonly used system. It is limited to 100m cable lengths so anything longer
will require optical fibre or radio links. There are a wide range of Ethernet products available to build your
network.
Fibre-optic Ethernet links
Fibre optic links can extend a Copper Ethernet network over several kilometres. You need a media converter
at each end to change between types. Optic fibre communications have a large advantage over Copper networks because they are completely electrically isolated, so problems with common mode noise and induced
voltages are eliminated.