We have a S7-1200 CPU 1215C DC/DC/DC firmware 3.0, we try working as a Modbus Client.

We try with TIA-V13 and TIA-V14 but no change in the server.

We also tried that PLC S7-1200 will be the server, 
but then the client could not connect to the server even 
though the Ping command works well.

We manage that STATUS parameters without any error, 16#0000

but data never transfered.

6ES7 215-1AG31-0XB0 is the product.

Any advice?

Thanks

MK

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Split from S7-1200 CPU 1215 communication with Modbus Server.

Hello all,

After we enter this line we got 80C8, connection to server fail.

We have full confidence in the server,
when another client of modbus leaves information on
the server everything works fine.

The S7-1215C IP: 172.16.14.78
The router IP : 172.16.14.254
Server IP : 172.16.17.8 try with new server IP: 172.16.14.240
No Error and no respond

Ping command from server to S7-1215C
Reply from 172.16.14.78: bytes=32 time=1ms TTL=29

We also try to write MB_Server in the S7-1215C, All data in MB_Server_DB was as they should be, but no client able to connect .
We got "TCP/IP CONNECTION TERMINATED" .

We try also server on IP:172.16.17.8 , MB Client on IP:172.16.14.240 => Data transfer good.
We try vice versa, data transfer very good.

I think we try any thing that we think about, it's look like our 1215C don't work in modbus TCP.

​Any idea to solve the problem will be welcomed.

Thanks

MK​

We found the solution .

Modbus device detection:

A Modbus TCP server is addressed using its IP address. For this reason, the MB_UNIT_ID parameter is not used in the case of Modbus TCP addressing.

The MB_UNIT_ID parameter corresponds to the field of the slave address in the Modbus RTU protocol. If a Modbus TCP server is used as a gateway for a Modbus RTU protocol, the slave device in the serial network can be identified using MB_UNIT_ID. The MB_UNIT_ID parameter would in this case forward the request to the correct Modbus RTU slave address.

Please note that some Modbus TCP devices may require the MB_UNIT_ID parameter for the initialization within a limited value range.

Our ID=1 and default is 255 :(

MK