The typical approach for using a paralleled port is to write to the port
directly without buffering. Most implementations of stepper controllers
using USB use either a buffering mechanism or interrupt driven data feed.
The actual throughput of a high speed paralleled port is on the order of
512Kbps. The standard through put of a USB 2.0 port is 480Mbps. The issue
of choppiness is one of the OS/Software implementation and not the hardware
port. The issue arises from the fact that writing directly to
the parallele port is much easier than writing directly to a USB port.
Again, the issue is in the software handling of the port and not the port
speed.
On Tue, Jun 26, 2012 at 10:24 PM, Tony Smith <ajsmith1968@...> wrote:
> ∗∗
>
>
> > 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
>
>
>
--
If you ask me if it can be done. The answer is YES, it can always be done.
The correct questions however are... What will it cost, and how long will
it take?
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