RE: EMC compatable computers

["j.guenther" <vze2z45u-at-verizon.net>]

The only thing that I can see that it offers that a parallel port does not
is the ability to have your keyboard, mouse, printer, scanner, camera, mp3
player, CD-ROM, dvd, memory card reader and who knows what else all on the
same port.  Never mind that the speed of many of these devices is hurt or
that it may not make sense to have all these on one port.  Everyone is after
low cost (cheap) computers these days and the less ports the mother board
makers can put on one the less it costs.

What we need in the home shop CNC world is a lower cost PCI alternative to
the STG cards.  We have PPMC from PICO Systems and can use that with a PCI
parallel port card.  We also have one or two "black box" solutions such as
DeskCNC from IMserv or DeskWINNC from DESKAM.  There is also the G2002
project from Gecko that looks promising and uses USB to communicate with the
PC.  Now what would be nice IMHO is if EMC could support the controller
board from DeskCNC or DesKAM.  This would take a new module to replace
steppermod, freqmod or stgmod that spit out the proper commands via a serial
port to run the controller board.  This should not be too hard to do but the
controller board people are going to have to release the software interface
details, which I hope they will consider doing.

John Guenther
'Ye Olde Pen Maker'
Sterling, Virginia

> -----Original Message-----
> From: emc-at-nist.gov [emc-at-nist.gov]On Behalf Of
> jmkasunich-at-ra.rockwell.com
> Sent: Friday, January 10, 2003 14:43 PM
> To: Multiple recipients of list
> Subject: Re: EMC compatable computers
>
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> Jon Elson wrote:
>
> > The problem with USB is that it only allows one
> > packet every milli-second.  I'm not positive
> > that is a real stumbling block, but it certainly
> > seems like it could be.  Especially if you wanted
> > greater than 1000 servo updates per second.  But,
> > even at 1000, the USB timer would be causing timing
> > jitter of substantial magnitude against the timer
> > EMC uses for the servo cycle.
> > It just seems like a real problem.
>
> I couldn't agree more.  I just don't get the infatuation
> with things like USB in this application.  USB offers
> high average bandwidth.  But it does not offer low
> guaranteed worst cast latency.  For CNC, latency is
> far more important than bandwidth.
>
> In addition, as far as I have been able to determine,
> USB requires some intelligence at both ends of the
> link.  It may only take a simple 8 bit PIC, but some-
> thing has to read the encoder counters and assemble
> the data into a packet.  That means hardware and
> firmware development.  Plus, there will always be
> some delay for packet assembly/dissassembly, protocol
> overhead, and so on.
>
> So what does USB offer that the parallel port doesn't?
>
> John Kasunich
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