On Sun, Oct 16, 2016 at 1:13 AM, Nicklas Karlsson <
nicklas.karlsso...@gmail.com> wrote:

> .
> > The master board sends the latch command on the parallel
> > port bus to other boards on the bus, as well as the
> > computer.  The computer would have the luxury of responding
> > before the next timer tick, nominally 1 ms.

Yes, this is how to do it but it requires two processors
  1) a big machine like a PC (or ARM cortex-A) that runs most of LinuxCNC
  2) A much smaller real-time processor that actually moves the signals
between #1 and the machine tools

You said a "latch" would work.  It would but only in the simple case of a
parallel output port.    You need to also worry about other kinds of data,
maybe even serial data or PWM . Also the data might not be going over
parallel port.  It might be Ethernet or USB.  New computers lack parallel
printer ports.

In a modern factory they have the computers in racks and maybe 100 meters
of cable going to the machines.  So I think yo might want to allow for a
large physical distance between #1 and #2.

I think the above is pretty much how the FPGA in the Mesa cards works.  The
PC sends data and parameters and the card generates waveforms and meters it
out in real time.


Chris Albertson
Redondo Beach, California
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