He would need STEP7 Classic (V5). If he purchase the very old (and cheap) CPU that I suggested, then it is not supported by TIA since TIA only supports the very latest S7-300 hardware.But if he uses the S7-300 he will need the TIA Configuration software, and the avaluationversion works only for 20 days or so, correct? This is why I believe the simulator would be better for the master, and for the Profibus DP slave, yes, I totally agree, the best is to get a used device from eBay.
If he dont have STEP7 already, then it is indeed an extra expense. Alternatively he could get the 30-day trial software.
My suggestion regarding the old S7 hardware is because for Profibus he will need some kind of hardware. And old S7 stuff is abundant and cheap. To my knowledge there is no such thing as a "Profibus stack" that you can install on a PC to work over a serial port for example.
When you mention "simulator for the master", do you mean there exist a software-based Profibus master for PCs ?
Anyway, I think that to learn about these protocols by simply listening in on the wires will be a big task, if not impossible. I wonder what it is that momo aims to achieve.