Re: Re[2]: digital servo controller to offload the Parallel Port?

[jmkasunich-at-ra.rockwell.com]

Richard wrote:

>
>
>jrrc> IMHO, Jon's PPMC is the right direction as far as the interface to
>jrrc> the PC is concerned.  The EPP port gives fairly fast and simple
>jrrc> access to external hardware.
>
> Again there's the legacy problem though. Parallel and serial
> ports are being phased out, as withnessed by the new breed of
> 'legacy free' motherboards that have neither.
>
> USB or Firewire looks the way to go IMO.
>

Call me a dinosaur, but as long as there are PCI slots, I'll
be sticking aftermarket EPP capable parallel port cards in
them for my PC based real-time hardware projects.

USB and Firewire may have lots of bandwidth, but they also
have lots of overhead on both ends, and they can have fairly
high latency - many microseconds to several milliseconds.
EPP's programming interface is as simple as inport() and
outport() on the PC side, and the outside interface can
be done with a few MSI chips, and no software at all.
Latency is single digit microseconds or less.

Besides, I don't want to connect any motion control hardware
directly to the motherboard of my PC.  I'd rather burn out
a replaceable parallel port card than a motherboard port.

John Kasunich