CP341 to Kepware OPC : Modbus TCP

Hi Modbus experts,

I am currently experiencing ModbusTCP communications trouble.
I want to read Modbus addressed data from a Siemens S7-300 via its CP341 card into my Kepserver OPC using ModbusTCP but I'm unable to establish good comms between the two, and it's starting to drive me nuts now.

CP341 SETTINGS
=============
Slave,
Modbus RTU,
19200,8,1,E
RS485 (two wire half duplex operation)
25blocks of data to be read

Modbus RTU to TCP CONVERTER
========================
Master
Same serial settings as the CP341
Assigned unique IP address on the network

SERIAL CABLE LINK
==============
Terminated as per Siemens CP341 documentation requirements (Two wire half duplex operation) between the CP341 and my Modbus converter unit.

KEPWARE OPC
===========
I can see all other existing (non siemens) Modbus slave devices happily on the network, but cannot see the CP341 only! Kepserver returns an exception code error 0x04 reporting a "Slave device error".



The SF light on the CP341 is clear, so there's no error on it. However the TX and RX green LEDs blink simultaneously every second. I've also used Modbus scan in Step7 to try detect the Master (Modbus RTU to TCP converter unit) but keeps returning an exception error or timeout message as well.

It's probably a simple config issue, but if anyone can bring to my attention anything glaringly obvious that I've missed, will be greatly appreciated!

Thanks guys, any input will be helpful.

Hi Jeffy,

Please ensure that your kepware OPC system and your Modbus converter unit are in the same network.

Just a comment, but why not use a Kepware OPC server that directly supports Siemens S7 ? Via TCP/IP or MPI or PRofibus ?

Now you want to do this:
S7 Program --> CP341 Modbus RTU Slave interface --> Modbus RTU master/TCP converter --> Kepware Modbus TCP OPC server.

You could have:
S7 Program --> Kepware S7 OPC server.

Will be much more performant, less expensive, easier to configure and more reliable.