Hi,
Mach does not work that way.
Mach3 (or Mach4) interprets Gcode and plans a trajectory. That trajectory is communicated to the motion controller
as a series of P(osition)V(elocity) over T(ime) data packets in 1 millisecond times slices.
The time slices are stacked up in a buffer, up to 250 millsecond or so long.
The motion controller, and for this purpose Machs parallel port driver is a motion controller, converts those time slices
into pulses. Mach at no time has variables that have pulse data, that is the job of the motion controller.
You do not have access to the motion controller data. In addition MODBUS is a serial communication protocol
and any sense of simultaneous pulses is lost, aside from the fact that MODBUS is way WAY WAY too slow
to communicate pulse timing.
If you wish to make your own motion controller you will need to use USB or Ethernet to get the PVT data packets and then
have your own motion control processor work out the pulse timing and generate the pulses. Its a very big undertaking.
All development of Mach3 ceased six years ago and it seems pointless to invest the sort of effort that would be required
for a software which is in its 'sunset years'. Mach4 is current and developing. If you were prepared to sign a N(on) D(isclosure)
A(greement) with NFS you could get sufficient information about Machs internal operation and the format of its PVT data
and make your own controller. Still a huge undertaking.
Is there a particular reason you want to make your own controller rather than use an off-the-shelf unit from any one of
a dozen or more different companies?
Craig