RE: digital servo controller to offload the Parallel Port?

[jmkasunich-at-ra.rockwell.com]

John Guenther wrote:

> What Les said is true but it would be really nice to have a
> lower cost solution to servo control with EMC than the STG card.
> Before you all flame me, I know that you can use Gecko 320 / 340
> drivers and the there is PPMC from Jon Elson and maybe some other
> solutions.  IMHO for home shop use the STG cards are really cost
> prohibitive, at least in my shop.

IMHO, Jon's PPMC is the right direction as far as the interface to
the PC is concerned.  The EPP port gives fairly fast and simple
access to external hardware.  The hardware offloads the time critical
task of generating step pulses, and EMC handles the servo loop.
I'm not crazy about Jon's divide-by-n step frequency generator, I'd
rather see a direct-digital-synthesis one like the one Mariss (Gecko)
is developing for his G2002 system.  The G2002 currently includes a
microprocessor, which I don't like because it has it's own software
to be written and maintained.  There is a Yahoo group called
"geckodrive", and several recent posts there discuss how the G2002,
with or without it's micro, might work with EMC.

I'd like to see a version of the G2002, without a micro, where EMC
can write directly to the Gecko step pulse generators using the
parallel port.  Advantages are good splitting of work between
hardware and EMC software (like PPMC), a nicer step generator,
(DDS instead of divide-by-n), and the low cost that comes from
Gecko because of their automated SMT assembly and test.  (Sorry
Jon, but you can't compete with Mariss's chip-shooter when it
comes to cost...although your FPGA based design might offset that
compared to his MSI design.)

My $0.02

John Kasunich