Modbus TCP gateway
Wieland Electric GmbH | BA000970 | 07/2019 [9855]
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There are two different methods of transmission for each transmission direction, i.e. samosPRO
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 memo-
ry 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 output da-
ta 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 simultaneously
address the SP-COP2-ENI module.
Table 24: Maximum number of possible Modbus TCP connections for the individual operating modes
Operating mode of the SP-COP2-ENI module Maximum number of connections
Output data (to PLC): Gateway writes
Input data (from PLC): Gateway reads
1 outgoing connection
1 incoming connection
Output data (to PLC): Gateway writes
Input data (from PLC): PLC writes
1 outgoing connection
6 incoming connections
Output data (to PLC): PLC reads
Input data (from PLC): Gateway reads
6 outgoing connections
1 incoming connection
Output data (to 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:
Gateway is master
Table 25: Configuration directive – gateway as master
Essential settings in the gateway configurati-
on (via SP-COP2-ENI)
Settings required for the PLC program and/or
in the Modbus TCP configuration tool
Choose
Gateway writes to tag/file
and/or
Ga-
teway reads from register
to configure the
gateway as a master.
–
Select which data are to be written to the PLC or
read from it.
–
