Homebrew PCBs

> USB 2.0 is used on a lot of direct stepping desktop and bench top mills.
So speed
> of the USB interface isn't an issue. What is an issue is the need for true
real-time
> support on Windows platforms. The Windows Kernel is the bottle neck of
such
> control systems. Not the USB interface.


Well, yes & no.

When people say USB is the problem they are comparing running a mill using
the parallel port, and then the USB port.  Even if you use a USB to Parallel
converter, the output from the USB/parallel is too choppy.  That's just how
USB works, it's fast but not as 'real time' as parallel.

In simple terms, talking to a parallel port (even under Windows) has fewer
delays than talking to USB.  You can predict the time it will take for a
message to be sent out the parallel port, with USB there will be tiny
unpredictable delays.

To use USB you need something like a Smoothstepper or Flashcut board, you
can view those as fancy USB-to-parallel converters if you like; they'll
buffer up the USB messages and send them to the mill at the correct rate.

Of course there's a premium for doing that, a parallel port is basically
free while a Smoothstepper isn't.  Then again if you want to run you mill
from a laptop...

Tony