Hello Ron;
In the late 90s I was presented with a software package called Cadepa. It was developped by Famic, possibly is still in use; they also developpe Automation Studio. You would develop your program in Grafcet (SFC), with symbolic names for all tags, and then compile the chart on any platform that you could buy the compiler for; you assigned hardware addresses for your tags at the compiler setup. It was a great tool for the technical school we were working at, we has a multitude of different PLC platforms (Square-D, Siemens, Telemecanique, Modicon) so students could see the same program (try to) run on whatever processor was available to them.
Drawback was that if you tried to look at the code directly it would be totally undecipherable; not practical for plant floor usage.
Hope this helps,
Daniel Chartier