RTU906/956 to Siemens S7 300 connection via RS485 (MPI/PB)


I have 7 PLC’s S7 300 with MPI/PB ports. Is it be possible to establish remote connection to those PLC’s using MPI/PB port which is RS485? I will appreciate any suggestion on this topic, from experience or not.



MPI is a proprietary protocol to Siemens. While MPI utilizes the EIA-485 (commonly referred to as RS485) standard as its physical layer, it operates with a unique communication protocol on top of it. Our devices are not equipped to understand or communicate using the MPI protocol.

Considering this, there are two potential approaches:

Firstly, for guaranteed communication with the RUT device, integrating a compatible communication module into your PLC would be necessary. This is because, although both systems use the RS485 electrical signaling, the communication protocols differ.

Secondly, if you have a RUT device already, you can try the Serial Over IP feature. Please keep in mind that I am not sure about the practical feasibility of this approach, and I cannot guarantee that this will work. I have not worked with MPI and did not test this. Essentially, Serial over IP function allows you to connect to the RUT device using TCP (or alternatively, UDP) and transmit data, which would then be transformed to serial data and relayed through the serial link. It’s crucial, however, to ensure that the data structure aligns with what the PLC expects. I suggest testing in a controlled environment first.

Kind Regards,

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