Re: [CAD_CAM_EDM_DRO] Re: Black box again

Alan Marconett KM6VV wrote:

> Hi Jon, Ballendo,
>
> I have noticed, that while you can get a parallel port board (SIIG) for
> the PCI bus, it may (always?) put the address not at 278/278h, but at
> something like C400h! And DOS won't recognize it! Fine for Windoz, but
> not good for "older stuff" (like me). Perhaps someone can shed more
> light on this subject!
>
> On the other hand, USB is called marginal on Windoz95, and nonexistent
> on 3.1 and DOS. Not that I mind Windoz98 2nd Ed, but I still like/use
> DOS.

Well, this isn't a problem for special purpose devices, as we control all
the software, we can adapt to whatever address things show up as.
Anyway, the parallel port address is configured by a line in the .ini
file for EMC, so it is user settable.

> Jon, I know you have your "black box" running already (and nearing
> production?), but what are your thoughts about USB control? Any
> possibility?

It is IN production, although there are only a few units installed so
far. The problem with USB is the huge overhead for protocol on the
CPU side, as well as the requirement of having a processor on the
device side. There is no processor needed in my current PPMC design,
it is all done with CPLDs and FPGAs. There was a lot of info indicating
USB was not a good choice for real time things that needed a lot of
transactions per second. We need to handle at least 1000 servo cycles
a second, and some users might demand more. My boards should be able to
handle 10 KHz without any trouble, and complete the full servo cycle
(read current position, compute new velocity and load velocity) in
about 25 uS when I employ all the IEEE-1284 bells and whistles. I'm
doing about 50 uS right now, using basic functions without much
optimizing.

> I seem to be getting into USB at work, on our hand held automotive test
> computer. And I hear of some projects starting up on these lists using
> USB's.

I'm sure it can work, and maybe will work best if you bypass all the protocol
drivers and go direct. Also, for EMC, we'd have to find a USB driver that
will work in the real time environment, which may or may not be easy.

Jon