Wieland samos PRO COMPACT - Configuration of the Modbus-TCP interface to the PLC - how the data are transferred

Modbus TCP gateway
Wieland Electric GmbH | BA000970 | 11/2016 (Rev. F)
52
Configuration of the Modbus-TCP interface to the PLC - how the
data are transferred
910785291
Application characteristics for Modbus TCP:
• Support of standard addressing conventions for Modbus TCP.
• Master and slave operation
Requirements for the PLC for Modbus TCP:
• The PLC must support the Modbus TCP protocol.
• The PLC must either support the Read Holding Registers and Write Multiple Registers
commands or the Read/Write Multiple Registers command.
The configuration steps in this section determine how the data are to be transmitted to the
higher-level PLC.
There are two different methods of transmission for each transmission direction, i.e. sa-
mosPRO COMPACT
to network
and
network to
samosPRO:
• Receiving method Polling/PLC requests (gateway as slave)
This method allows the PLC regularly to request data using polling.
When this method is used, the data are returned in the response to the data request. The
PLC requests data by accessing the receiving data address of the SP-COP2-ENI module via
a read-holding-register telegram.
• The master receiving method gateway writes to the PLC (auto-update, gateway as master)
When the SP-EN-MOD module sends data to the PLC, these are immediately written to a
memory location in the PLC.
• Slave transmission method - PLC writes (gateway as slave)
With this method, the PLC sends telegrams to the SP-COP2-ENI module to write to the
output data sets. For this purpose, the PLC writes data into defined addresses.
• The master transmission method gateway reads from the PLC (auto-update, gateway as
master)
With the master transmission method, the SP-COP2-ENI module polls the PLC for the out-
put data sets.
NOTICE
The configuration is regarded as faulty when the IP address of the PLC is zero and the read
transfer mode and/or write transfer mode has been set for the master.
The number of possible connections to the PLC depends on whether the SP-COP2-ENI module
is operated as a master or as a slave. Depending on the setting, up to 6 PLCs can simultaneou-
sly address the SP-COP2-ENI module.
Table 18: Maximum number of possible Modbus TCP connections for the individual operating modes
Operating mode of the SP-COP2-ENI modu-
le
Maximum number of connections
Output data (to the PLC): Gateway writes
Input data (from PLC): Gateway reads
1 outgoing connection
1 incoming connection
Output data (to the PLC): Gateway writes
Input data (from PLC): PLC writes
1 outgoing connection
6 incoming connections
Output data (to the PLC): PLC reads
Input data (from PLC): Gateway reads
6 outgoing connections
1 incoming connection
Output data (to the PLC): PLC reads
Input data (from PLC): PLC writes
6 outgoing connections
6 incoming connections
The following table describes the configuration, depending on the transmission method:
6.3