i want to make profibus FMS data exchange between two s7-300 PLC via their CP343-5 in both side

-what are the most important steps to configure this type of  liaison

-how many maximum number of octets which can be send via this connection

Hello narove;

1- FMS has been abandoned for a while now, in favour of Ethernet communications, since they operated at the same level (message-wide protocols) and Ethernet found favour in the industry.

A few years back I saved a chapter of the NCM S7 for Profibus manual which describes different Profibus connections available on S7 CPs (DP master/s;lave, FDL, FMS), with sample design suggestions. Chapter 6 describes the essentials of communicating over FMS between 2 S7 CPUs. You will find it as an attachment, since I can't seem to locate a download link for that particular manual now .

If I remember well, the most important aspect is to create a proper FMS variable, indexed, before attempting to exchange data.

Follow the step-by-step example, pay attention to the definitions and the details and do not cut corners; that is how I started working with FMS . You should be alright.

2- Size of the maximum data exchange per job (you can create more jobs, call them sequencially)

SIMATIC NET NCM S7 for PROFIBUS / FMS volume 2

On an FMS connection, the PROFIBUS CP can transmit an FMS protocol data unit (FMS PDU) with a maximum length of 241 bytes per job.

Hope this helps,

Daniel Chartier