Well scorp, I am truly new to LOGO and couldn't figure out how to do a pulse generator.

In an empty project file, I just did this :

1 : i wired a push-button (physical wiring, not programming) to I1

2 : set up a modbus server.

that's all I know for now (see attachment)

Should this step be enough for a modbus client to see the inputs ?

if not, please advise me what I should do next.

I don't know, if it is possible to communicate without a program. I think so that it's enough. With a little test program you are able to look for different functions of Modbus, see attached test program. There are comments for the right registers and the function codes you can see in my table.

If have activated 2 servers, Modbus and S7. You can delete one of them, but it doesn't matter for testing with both servers.

Regards, Scorp