Homebrew PCBs

On Tue, Jun 11, 2013 at 12:19 PM, Andrew Hakman <andrew.hakman@...> wrote:
> Most "USB to parallel" adapters do not do what you think they do. They only
> work for printers, not general parallel devices. All the CNC machines use
> parallel so they can have a much dumber controller, and just diddle the
> bits of the parallel port for driving the steppers, and may rely on
> hardware interrupts and the very low latency of the parallel port for
> timing.

Yeah, then you need wretched software like MACH3 or EMC2 running
full-time on a PC to do the real-time stuff.

> I'm not sure why someone hasn't come up with a generic
> microcontroller based controller that does the same thing with the generic
> I/O pins, and takes the gcode, or something else at a 'higher level' over
> USB, as the timing over USB is not good enough to drive the motors
> directly.

You mean like this?

  https://github.com/grbl/grbl

GRBL takes your G-code via serial USB, and does all the motion
control, including motion lookahead to make everything smooth.

GRBL is an absolute miracle, I don't know why anyone would bother with
the parallel port.  Highly recommended.

Mitch.