Hi Steve,
Yes, unfortunately, Sim doesn't seem to cut very well for me.

. You know what they say,
“In theory, theory and practice are the same. In practice, they are not.”
Since I was able to use the code with Mach3 and uc100 one would think it would work the same way using the same hardware with Mach4 and the new uc100 plugin. Testing it against real hardware in real time is the only reliable method. If it works on a lathe with Mach4 and Pokeys or pmdx controllers then it would point to the uc100 as the culprit or Mach4 if it fails for them. Or if someone else has a uc100 and Mach4 and can't reproduce my error then it would point to my hardware or installation.
I think