I added a parallel port pendant to my Mach 3 controlled mill some years ago.  It has rotary switch selectors for axis and movement increment, with mpg and estop.  There is a button on the side to "load the settings".

The brains are pretty straightforward, NoOp-ing the selection lines.  Another brain uses the rotary switch outputs combined with the side button to "implement" the settings - invoking "JogOn."   So, you have to first set the rotary switches, then press the side button.

Is there a better way to do this?  I would like it to be ready to go immediately after setting the axis and increment.

I stopped using Mach3 some years ago but, nevertheless, find attached brains that I used on one machine with 2 LPT ports

Thanks.  I'll look at it.  I'm still using Mach 3 and parallel ports - because it works fine.   I use a 16 year old Win XP machine with solid state hard drive, not connected to a network.  Vectric Vcarve is on it too.  If it ain't broke ...

I gather that Mach 4 wants a newer machine.