Interfacing to the ISA bus is dead simple...  in fact, you can buy
prototyping boards (from JDR? Jameco? One of the two...) with the
interface circuitry already etched and ready for the $.50 worth of parts
it will take.  Buffer the data bus, decode the address bus to select a
memory or I/O address range, you're pretty much done.  It's *very* close
to an 8086 processor bus, buffered and latched.  I've done it on a couple
of products, one of which was even a little bit of a commercial success,
at least by my standards of the time -- I think the Air Force may still be
using them.  The ISA interface was a single Lattice GAL16V8, I seem to
remember, plus a 4-position DIP switch for address selection and an LS24x
something or other buffer.  No need to use an IRQ or DMA unless you need
'em, which is unlikely in most cases.  Figure a few bucks and a couple of
hours to do the whole thing.

EISA - forget it, it's dead.  VESA - use the ISA portion of the slot.
Microchannel - again, forget it, it's dead, but if you must you could
maybe do it for a couple hundred bucks and a few thousand hours of work.
PCI - well, I would guess you best bet would be to use a PCI interface
ASIC.  That, or use the ISA slot still present in most systems, or go USB
if you're worried about volume sales to new systems purchasers.  In any
case, figure a ***lot*** of time and some substantial money getting it
figured out, I think.  It's great for volume production, lousy for
one-offs.

Someone mentioned the SM bus - I have not looked for any docs on this, but
I would be downright astonished if all system board vendors were using the
same hardware and interface methods.  If they are, though, it would be
cool -- though not one of my system boards has a header to connect to that
bus.

Overall, barring strong reasons to the contrary, I'd go with an 8-bit ISA
board.  Not glamorous, but effective.

Dale
--
Hallo, this is Linus Torvalds and I pronounce Linux as Leennuks.
Hallo, this is Bill Gates and I pronounce 'crap' as 'Windows'.

On Fri, 9 Nov 2001, Jinx wrote:

> > What bandwidth do you need?
>
> Nothing special. Obviously with a potential 33MHz or 66MHz (~100Mbps)
> available on a PCI slot the data to and from the PIC will need to be managed
> somehow. Still reading up on PCI specs/protocols/requirements. I imagine
> the EISA/ISA would be more friendly, being an older system with more
> user board specs available
>
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