Hello juju;

The ATV series of drives is developped by Schneider, and they all are Modbus slaves natively.To my knowlkedge they generally support RS-485, please make sure that your ATV 31 has a RS-232 communication port. as the following information would have top be slightly modified.

Here is a link to Schneider documentation on Modbus communications to an ATV 31:

ATV31 Modbus manual - Documents & Downloads

So you would need a RS-232 Modbus master in the S7 system. One option that can be mounted in the main rack of a S7-300, or as part of a Profibus-DP remote IO ET 200M, would be a CP 341, with a Modbus master loadable driver (with physical dongle):

SIMATIC S7-300/S7-400 Loadable Driver for Point-to-Point CPs: MODBUS protocol, RTU format, S7 is master

There are other options of course, depending on the S7 system you are using.If you have a ET 200S CPU (IM 151-7 for example) you could usew a serial CP 1SI as Modbus master, which would be a much cheaper solution (no loadable driver to purchase).

Hope this helps,

Daniel Chartier