Re: [CAD_CAM_EDM_DRO] Interface options, headless boxen, and remote control ...

RS-422 / 485 is still a serial device. There's just so much you can do with
a serial
data stream with a UART or USRT that is decoded in the PC's I/O space when
reading
and writing to a device at the end of the pipe. I've designed motor
controllers using
RS-485 links with microcontrollers and they work great. But it's not a good
design
for a CNC control.

I looked at microcontrollers hanging off a serial port. I even built one.
Still it was
too limited by the serial pipe. Plus you have to rewrite the code that's
already been
written to parse the G code and put the code to do the interpolation out in
the micro.

I don't care at all for the parallel port either.
It's greatly limited and is a kludge for CNC due to the way it was designed
for parallel
printers back in the early 80's.

A few years ago I designed an ISA card that provided a several 8 bit ports
and used a
37 pin connector like the Ahha card does. It used a simple PLD for address
decoding.
That was good for several axis of I/O but still was limited by the 37 pin
connector. So
I added another 25 pin internal ribbon cable connector and added a 25 pin
slot mounted
connector. It was still limited by the fact it was just a dumb I/O port.
All the load is on
the OS and host processor.

I've been looking at this for a few years. ISA was the way to go. But those
days are
gone. ISA is a dead bus and is going away.

Welcome to the world of PCI. There are PCI parallel multiport cards that
could
be used but you are still limited when you get into 4+ axis with full limit
switches.

I've been kicking around the idea of designing a PCI card to do CNC I/O
with.

So about a month ago, I decided to commit $$$ and time to it. The card will
be a 32 bit PCI
card with lots of on board memory for step buffer, timers, counters, encoder
interfaces,
spindle interfaces and lots of auxillary I/O. The design has been started
and if all goes
well, in a couple of months I'll have the first prototypes running. I'm
thinking 6 axis but
8 axis might make it in there. It will support steppers as well as servos
and could even
be used to run steppers in closed loop mode with encoders.

I'm also talking to a DSP guru buddy of mine about adding a DSP chip to it.
I'm not a DSP expert but can see how an off board DSP could help in some
of the calculations CNC requires.

The PCI card will cable to a breakout box where all of the connections to
the real
world will be. I'm kicking around the idea of an optical interface to the
breakout box.
If not optical it'll be differential to the breakout box for noise immunity.

I'm going to try to do it right. My hope is to end up with an interface with
an open API
that anyone that wants to can write code or drivers for that will be a
viable interface
for several years to come. But one that is affordable to build.

Linux and EMC is not my first priority. I prefer Windows. But I'm sure I'll
find someone that
will be willing to write Linux drivers for it.

If nothing else, I'll finally have the interface I have wanted for years.

later,
Larry E.

----- Original Message -----
From: "Bryan-TheBS-Smith" <b.j.smith@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, August 19, 2001 8:30 AM
Subject: Re: [CAD_CAM_EDM_DRO] Interface options, headless boxen, and remote
control ...


> Larry Edington wrote:
> > RS-232 ports just aren't fast enough for high step speeds.
>
> I'm starting to realize that.
>
> > USB is closer to the required speed but as you, I wouldn't
> > trust a USB CNC controller and feel it would largely be a waste
> > of time to develop one.
>
> My view _exactly_.
>
> > Firewire is a better option than USB but has it's downsides
> > as well for CNC.
>
> It would be like making a SCSI interface. Not ideal.
>
> What about RS-422? At short distances (<10'), it can do upto
> 10Mbps. You can also use RS-485 if you need to control more than
> one device. Various multiport boards are out there that can do all
> RS-232, 422 and 485 (for only a couple hundred $$$).
>
> The "problem" here is how to "handle" it on the CNC side. Sure, we
> can jack up all kinds of performance on the Linux PC/EMC side, but
> what kind of designs and ICs do you have on the controller side to
> handle this?
>
> I guess I need to do more research on the end-components before I
> comment anymore.
>
> -- TheBS
>
> --
> Bryan "TheBS" Smith mailto:b.j.smith@... chat:thebs413
> Engineer Absolute Value Systems, Inc. http://www.linux-wlan.org
> President SmithConcepts, Inc. http://www.SmithConcepts.com
>
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