I'm in need of something like the old SST-PBMS-PCI card that could simulate multiple Profibus nodes. Another choice could be the ProSoft AN-X-PB that also does multi-slave communications. However both of these appear to be unobtanium at this point in time.

The goal is to build a simulator for testing Siemens PLC code without needing to stop the entire plant for testing.

If this is the wrong forum -- please tell me.

 

You could also use Pro-face touchpanels that act as the Profibus slaves.

During my times working with the ObjectAutomation PLC, we designed the PLC software in such a way, that every part in the software had a "simulation" bit input.
When this input was high, the part of the software acted without actual IO and simulated signals by software.
So by just switching on this bit, we could simulate the whole feed plant without actual IO.
It worked marvellous.