Data Exchange - WAGO -I/O-SYSTEM 750 User's Installation And Configuration

3.2.5

Data exchange

With the ETHERNET TCP/IP fieldbus controller data is exchanged 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 controller of the WAGO-I/O-SYSTEM 750 nor-
mally are slave devices. Due to the programming with IEC 61131-3, control-
lers can additionally assume the master function.
The master makes a query for communication. By adressing this query can be
sent to a specific node. The nodes receive the query and return a response to
the master, depending on the kind of query.
A coupler is able to produce a certain number of simultaneous connections
(socket connections) to other network subscribers:
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The maximum number of simultaneous connections may not be exceeded. If
you wish to establish further connections, terminate existing connections first.
For a data exchange, the ETHERNET TCP/IP fieldbus controller uses three
main interfaces:
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Data exchange takes place between the MODBUS master and the bus modules,
between the PLC functionality of the PFCs (CPU) and the bus modules as well
as between the MODBUS master and the PLC functionality of the PFCs (CPU).
The master accesses the data via the MODBUS functions implemented in the
controller.
PFC access to data is then made by means of an IEC 61131-3 application pro-
gram, whereby data addressing is different.
Modular I/O System
ETHERNET TCP/IP
1 connection for HTTP (read HTML pages from the controller),
3 connections via MODBUS/TCP (read or write input and output data from
the controller),
2 connections via the PFC (available in the PLC functionality for IEC
61131-3 application programs) and
2 connections for WAGO-I/O-PRO (these connections are reserved for de-
bugging the application program via ETHERNET.
For debugging, WAGO-I/O-PRO requires 2 connections at the same time.
However, only one programming tool can have access to the controller.
interface to the fieldbus (master),
the PLC functionality of the PFCs (CPU) and
the interface to the bus terminals.
Fieldbus controller 750-842 • 65
Data exchange