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Operating Instructions
Chapter
5
Flexi Soft Gateways
8012664/XB29/2013-06-11
© SICK AG • Industrial Safety Systems • Germany • All rights reserved
77
Subject to change without notice
Ethernet gateways
5.3.3
Configuration of the Modbus TCP interface to the PLC — How the data are
transferred
Modbus TCP application characteristics:
support of standard Modbus TCP addressing conventions
Master and Slave receive methods
Modbus TCP PLC requirements:
The PLC must support the Modbus TCP protocol.
The PLC must support the Read Holding Registers and Write Multiple Registers
commands or, alternatively, the Read/Write Multiple Registers command.
The configuration steps in this section specify how the data to the higher-level PLC are
transferred.
In general, there are two different transfer methods available for each transfer direction
such as
Flexi Soft to Network
and
Network to Flexi Soft
:
Polling receive method/PLC requests (gateway as slave)
This method provides a polling method that allows the PLC to request data on a periodic
basis. In this method, the data is returned in the response to the data request message.
The PLC requests data by accessing the receive data address on the FX0-GMOD module
with a Read Holding Registers message.
Master receive method — Gateway writes to PLC (auto-update, gateway as master)
When it is determined that data received on the FX0-GMOD module backplane interface
is to be sent to the PLC, the data is immediately written to a data memory location on
the PLC.
Slave transmit method — PLC writes (gateway as slave)
In this method, the PLC will send write messages to the FX0-GMOD module to set the
output data sets. To write to the output data sets, the PLC writes the data to specified
addresses.
Master transmit method — Gateway reads from PLC (auto-update, gateway as master)
In the master transmit mode, the FX0-GMOD module will poll the PLC for the output
data set settings.
The configuration is considered faulty, if the PLC IP address is zero and either the Read
Transfer mode and/or the Write Transfer mode is set to Master.
The number of possible connections to the PLC depends on whether the FX0-GMOD is
operated as a master or slave. Depending on the setting, up to 32 PLCs can address the
FX0-GMOD at the same time.
Operating mode of the FX0-GMOD
Maximum connections
Rx (To PLC) transfer mode: Master
Tx (From PLC) transfer mode: Master
Rx and Tx: 1
Rx (To PLC) transfer mode: Master
Tx (From PLC) transfer mode: Slave
Rx: 1
Tx: 31
Rx (To PLC) transfer mode: Slave
Tx (From PLC) transfer mode: Master
Rx: 31
Tx: 1
Rx (To PLC) transfer mode: Slave
Tx (From PLC) transfer mode: Slave
Rx and Tx: 32
Note
Tab. 59: Number of possible
connections