VMax,
Here is my understanding (which can obvioulsy be wrong), but, It is my understanding with out a Plug in, then the "Z" is controlled up and down by an analog motor in relation to the Plazma current draw.
So, you would have a "Z" axis that is controlled UP and Down by Mach (the standard Z), and then another "Z-Head " that is controlled up and down by an analog motor that is driven through a PID loop that is in a PLC, or Plazma Controller, or from a "Plug in for Plazma", or some combination of the above.
It is my understanding that when "G-Code" is actually running in Mach3, The "Index" and "Head" of the Buffer are NOT together, and when they are NOT together, that disables any type of "Jogging" in standard Mach. BUT, if you write a Plug in, in which you CAN have direct control over jogging, then you CAN override this behavior. It is NOT wize to do so, and it will cause you problems. (Found out the hard way, when I started writing my Jog Plug ins).
I think Mach give Tourch/Plazma control signals that you can work with, but they are not step and direction signals. Most of the stuff, and I think
Brian wrote an "Analog PID Loop" Plug in just for the above issues. I think that Bob Cambel and that crowd that sell Plazma Boxes, all use some type of Current Adjusted Z-Head that is controlled as an analog PID loop somewhere.
scott