Re: New project...PCI based servo control board

[jmkasunich-at-ra.rockwell.com]

Jon Elson wrote:

> jekasunich-at-worldnet.att.net wrote:

>> Craig wrote:

>>>>> One closing thought on board #2, I'd like to consider
>>>>> a SIMPLE bus expander be included on it

>>>> Excellent idea!  Why waste FPGA gates on simple input and
>>>> output ports. Let the FPGA implement an expandable bus.

> Ah HA!  I KNEW it!  You'd eventually reinvent what I
> already have been doing.  Except, the PC ALREADY has
> an expandable, bidirectional, 8-bit data bus!
> The EPP Parallel Port!  its fast, very low CPU load
> (1 cpu instruction/byte transferred) the protocol is
> totally managed in hardware, etc.
>
> Jon

I'm not that suprised to see similarities between this
project and your boards.  After all, we are all trying
to solve pretty much the same problem, so our solutions
will tend to look pretty much the same.  Besides, when
I see good ideas I don't hesitate to use them, and your
boards have many good ideas in them.

There are differences though:

This project is physically mounted in a PC slot, allowing
it to use the PC power supplies to save cost.  (This applies
to the PCI and ISA versions.  I'd also like to have parallel
port and/or ethernet versions.  Those would require external
power supplies.)

This project separates the brains from the machine interface,
and makes the interface completely open, so the user can have
as much I/O as he needs, without paying for I/O he doesn't
need.  This includes both standard digital I/O, the analog
or pulse outputs, and the encoder inputs.  The user can have
any mix of Opto-22 outputs and relay outputs and TTL outputs,
for example.

This project is aiming at somewhere between 6 and 8 axis,
rather than 4.  I know you can add another board to your
system, but that doubles the cost.  I'd rather spend a
few bucks to make the FPGA bigger, and let the user add
as much or as little I/O as needed.  In the long run, the
money is in the machine interface.  I think you mentioned
that you have about $90 in terminal blocks in the PPMC,
and quite a bit less than that in FPGAs.

This project will supply any mix of analog and pulse
outputs.  Yours is either all analog (PPMC) or all pulse
(USC).

And yes, I still agree with you that EPP is a nice clean
interface, and I prefer it over PCI.  The only downside
of EPP is the need for a separate power supply.  I'm
starting to think that ISA is the best of both worlds,
as least if you have an ISA slot available.  Simple
interface, and available power at +5, +12, and -12V.

Craig is strongly in favor of PCI, which is fine.  He
has the skills and tools to do that.  My contributions
to the design will be in the control hardware and machine
interface sections.  My work will be completely open, and
I hope to make ISA and EPP versions available on my
website.

John Kasunich