Re: PCI card

[John Griessen <john_g-at-cibolo.com>]

Hi Mark,

I think industrial ethernet is a better way to think of how to get past
obsolescence of parallel ports also.  Although it will be a few years at
the minimum before there is any parallel port obsolescence problem, and
then it will only be a price problem.  There is a nice VIA mainboard
that is the smallest mini-ITX size that comes with parallel ports and is
aimed at the embedded market.  Aiming at the embedded market means the
serial and parallel ports will stay withthem longer than the mainstream
motherboards. A VIA EPIA mainbaord costs about $110 at Fry's and has all
peripherals and one PCI slot, then $30 for memory and $40 for a
mini-sized case and a $70 hard drive and you have a 600 MHz EMC system. 
It's even fanless so you can have few dust accumulation problems.  
Expensive industrial grade computer boards will be available with
parallel ports for long time frames -- that's part of why some
industrial boards are specified -- that the maker promises to keep
delivering and not change them rapidly.  The VIA board isn't quite
industrial, but close.

For offloading function from the PC to something closer to the motors,
industrial ethernet will be good also.  There are even ways to have some
links be over plastic fiber and compatible with copper twisted pair
ethernet for the rest, all passing along the same data.   Plastic fiber
is a bigger benefit than cheap available port cards, since it gives
noise and voltage drop immunity in an environment where voltage drop and
noise are real hazards.  Big motors will cause drop, especially when
some metal cutting tool bites off more than it can chew.  controls to
many motors are noisy, and someone might be plasma cutting nearby too.

PFGA's are not a hit with many folks on this list -- it's a rather large
design task to use them -- lots of resistance compared to
microcontroller programming.  And then there's resistance to external
microcontrollers too, since they have their own time and effort hit
compared to programming on a PC.  The place to study more, (I've been
studying other stuff for my work and have not dug into it yet), is in
the EMC documentation about the place in the code where the real-time
part hands over and receives data from the non-real-time part.  It is
done in a way that is planned so it can be done in a specific physical
memory location outside the PC rather than just in an allocated memory
range setup by software in the PC without you thinking about it.
Those memory locations can be put at the other end of an industrial
ethernet network pretty much by the ethernet chips alone, and then
either hard logic (or FPGA) or a microcontroller could use the ethernet
chip I/O registers to run motors and listen to sensors.

John Griessen 
Austin Texas

On Sat, Feb 15, 2003 at 12:26:25AM -0500, Mark Pictor wrote:
> looks to be the way to go, though it would still
> require someone familiar with the VHDL language.
> 
> FPGA? core? VHDL? An FPGA (Field Program

On Sat, 2003-02-15 at 00:49, John Sheahan wrote:
> If you are going to do the real-time offload - choosing
> something with a lot less wires / longer range makes 
> more sense to me.
> 
> The prior suggestions for ethernet seems sensible for this 
> part. Put the real time external controller in a fpga or real-time
> cpu or dsp (as suits the individual - I'd personally choose 
> the fpga).  Keep the PC inside, not in the workshop.
> 
> john