Fieldbus coupler 750-342 • 31
Data exchange
Modular I/O System
ETHERNET TCP/IP
3.1.5 Data
exchange
Process data exchange with the ETHERNET TCP/IP fieldbus coupler occurs
via the MODBUS/TCP protocol.
MODBUS/TCP works according to the master/slave principle. The master is a
superimposed control unit, i.e. a PC or a PLC device. The ETHERNET
TCP/IP couplers of the WAGO-I/O-SYSTEM are slave devices.
The master makes a query for communication. Through adressing, this query
can be sent to a specific node. The nodes receive the query and return a re-
sponse to the master, depending on the kind of query.
A coupler can communicate with a certain number of simultaneous connections
(socket connections) to other network subscribers:
•
1 connection for HTTP (reading HTML pages from coupler) and
•
3 connections via MODBUS/TCP (reading or writing input and output data
from coupler).
The maximum number of simultaneous connections cannot be exceeded. If
further connections are to be made, terminate existing connections beforehand.
For a data exchange, the ETHERNET TCP/IP fieldbus coupler is equipped with
two interfaces:
•
the interface to fieldbus (-master) and
•
the interface to the bus modules.
Data exchange takes place between MODBUS master and the bus modules. The
master accesses the bus module data via implemented MODBUS functions.