Re: wild I/O interface idea

[Doug Fortune <pentam-at-home.com>]

Jon Elson wrote:

> Doug Fortune wrote:
>
> > Regarding the previous ISA/PCI/USB/ethernet etc
> > conversations on how to get signals out to/from the real world
> > in a timely manner for steppers and servos.
> >
> > Once upon a time I built an analog/digital converter
> > for an Atari/ST and it did its I/O through the cartridge
> > game port - essentially memory mapped I/O at memory access speeds.
> >
> > I am thinking of a card, which to the computer looks like a
> > SDRAM memory stick, but which actually is not memory,
> > but otherwise provides three basic functions:
>
> No, you can't do this on a Pentium, or other cached CPU, as
> the memory location may not be updated for seconds after the
> CPU executes a write to memory command.

I am sure there are a number of 'gotchas', but one always finds
a way around them.

> The other problem is designing a device that
> can operate at 133 MHz bus speed.  Can you design an I/O
> chip that can handle 2 I/O commands separated by only 7 nS?

The above A/D had a cycle time of 4 ns, and that was 15 years
ago (using discrete ECL logic and ram).  133 Mhz is a walk in the park.

Well, I've got too many projects already on the go.  Perhaps I'll let this
one percolate a while.

The good news is I got my home-made 4 channel parallel port L297/L298
board working, running 3 steppers on the bench.  Until I get EMC going
I am using KellyWare's KCam3 (Win95/98) with great success because
it is so fast and simple to set up (and free these days).  Give it a try.
http://kellyware.com/kcam/kcam.html

No, I don't have pictures of the 4 channel board yet.  Its a bit of a mess
and I'm going to try making a pcb with Linux/PCB.
http://bach.ece.jhu.edu/~haceaton/pcb/