Technical data

62 Theoretical and general applications www.westermo.com

Modbus Plus

Modbus Plus is an industrial application network that utilises token exchange, peer-to-

peer communication. Token exchange and peer-to-peer involves communicating over

a logical ring where all nodes can initiate communication, however, a node can not

send until it has obtained the token. The transfer rate is 1 Mbit/s over screened twist-

ed pair cable. Modbus Plus is an open network for information exchange between

nodes in the network, which creates the possibility to control and monitor industrial

processes.

The network is transparent, i.e. it is possible to reach all system devices via the

connection point.

The interface is based on RS-485 and consists of sections where up to 64 nodes can

be connected to each section. Up to 32 nodes can be connected directly to a cable

segment, maximum transmission range on one segment is 450 metres (1476 ft).

A repeater can be installed when greater distances are required, or when more than

32 nodes need to be connected to one segment. The maximum section length is

1800 metre (1.11 mi), or you can use a fibre optic modem for longer distances.

MODBUS/TCP

MODBUS/TCP is a variant of MODBUS, a straightforward supplier independent com-

munications protocol for control and monitoring of automation equipment. The pro-

tocol utilises the properties of MODBUS with the communication media being the

TCP/IP protocol which can traverse intranets or the Internet. It is possible to encapsu-

late a Modbus ASCII or Modbus RTU packet into a TCP or UDP packet using a serial

server, this is not the same as ModbusTCP. In modbus TCP each node knows its IP

address and communicates on TCP port 502.

Up to 32 nodes, max 450 metres (1476 ft)

Min 3 metres (9.84 ft)

Node

End node

Terminated

End node

Terminated

Node

B A C K