4 MODBUS
MODBUS is a master/slave system. The master is a superimposed control unit, e.g. a PC or a PLC device. The MODBUS coupler/controller of the WAGO-I/O-SYSTEMS are slave devices.
Bus conflicts do not occur because only one node is sending. The master makes a query for communication. This query can be sent to a specific node or to all nodes as a broadcast message. The nodes receive the query and return a response to the master, depending on the kind of query.
Fig. 4.1: Example of a MODBUS topology
This bus topology is only valid for the variants with the RS 485 interface. With RS 232 it is only possible to have a peer-to-peer connection.
You will find further information on MODBUS in:
Online information on MODBUS: http://www.modicon.com/techpubs/toc7.html
MODBUS tools for PC: |
http://www.win-tech.com |
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