Signal Conversion Profibus to Modbus


Thread Starter

Andreas Ramsbacher

I'm on a mission there I will try to collect some signals from a Siemens S7 400. My problem is that my device only can talk Modbus, LON, Bacnet. My idea is to convert the signals on the Profibus (field bus) to Modbus, but I haven't a clue how the Profibus addresses work.

Patrick Lansdorf

Hello Andreas,

I work for a company called HMS and we make gateways and fieldbus interfaces. We have a gateways that convert profibus to modbus. We have several different types, both master and slave interfaces. Your name suggests that you are german speaking and we have a branch office in Karlsruhe. I suggest that you contact them for more info:

//Patrick (Support at HQ)


I had a similar problem/struggle a while ago.

My advice is to go for Modbus (If serial, use RTU). Siemens actually have modbus driver blocks (Which has to be purchased) for the S7300/400 and by using a RS232/485 Module/card.

Initially I tried the protocol converter units, and had a lot of trouble (Swapping Bytes, and different modubus versions 984 etc.) I just couldn't get the module to work properly.

At the end, I programmed a solution, using S7-200 and EM277, which acts a a DP Slave to the S7-400.

The advantage was that I could swap bytes, do scaling and do communication monitoring if required... I also implemented a Async Tx/Rx block on both sides to transfer more data on Profibus (Small Cyclical frames, but large amount of Data).
Strange enough was that the solution was in the same pricing range as the modules...

I think the price for S7-400 card, Protocol converter modules or my pre-packaged solution are all similar.



I normally use HMS products like Anybus or Schneider Electric LUFP gateway (that seems to be HMS) and sometimes Prosoft Prolinx range.

I am using HMS converter from Profibus to Modbus.

I Already used the S7-200 as you said but only with RS485 2 wire slaves, with 3 wires I couln't !!

Now I am facing a problem with HMS converter because the slaves doesn't reply all requests, they say that is a problem of a time too short between requests.

Best Regards

Atif Sarfraz

I want to convert Profibus to Modbus TCP/IP. I am using Hilscher NT 100 RE DP Module as Master and Siemens EM277 as Slave. I configured the X2 port as Open modbus (RJ45) and X3 as the Profibus Master.

I checked with the Hilscher Diagnostics and proved that Hardware configuration is Ok. I can observer the proper LED feedback from the EM277 and Hilscher but i cannot acquired the V2900.0, V2900.1 address

Is there any Genious Guy for help.


Eric Ratliff


Not sure if you have Modbus TCP (Ethernet) or Modbus RTU (binary over serial) or Modbus ASCII (ASCII over serial).

For the Ethernt or Serial case, there is GW-7553. This allows a Modbus master or slave of TCP, RTU, or ASCII type to communicate with a Profibus master. See .

For the serial case there is GW-7552 . This lets a Profibus master communicate with a modbus RTU or ASCII slave or master.
It is very easy to solve it.

You can use CP-341 as S7-300 modules if you are using ET200M de-centerlized topology or you can use the CP-441 (Serial communication processor) on the S7-400 rack and you can use the dongle of Modbus slave and your system will act as the master to the S7-400.

In the configuration backage of the CP you will find a place where you configure which data to be sent of the modbus side and you just need a very few programming on the siemens side to write the required data to the specific locations you have specified in the configuration package.

Best regards