I opened up some antique Adacom fanout boxes the other day and found
some nice mini switchmode PSUs and lots of LEDs and Ethernet sockets
with their own pulse xformers and bit-repeater circuitry.  Aha, I
thought, toyboxes for networked PICs! :-)

However, it brought some questions to mind.  There's no chance of a
bare PIC keeping up with Ethernet bit rates, especially bearing in mind
the sync problems, but it must be possible to put some fast hardware up
front to relax the timing requirement.  I don't have any specific use
in mind, but I am curious as to what's possible and what's not, cheaply.
(Putting an Ethernet controller in there defeats the whole idea.)

Fairly simply, a long shift register could be used to capture passing
Ethernet frames on a one-shot basis (only one frame accepted until the
PIC releases the interlock).  All the paraphenalia of CSCD/MA can be
ignored on input because the CRC will be incorrect if a collision
spoils the frame, and the PIC can easily check that in its own time.
[Or, to keep costs low, it might be possible to use a double-buffered
8 or 16-bit shift register and use the PIC to parallel-load it into
an external memory buffer on the fly -- tight timing, but not too bad.]

Something like that could form the basis of, at the very least, yet
another PIC programmer :-), albeit networked, or an interesting home
automation module for those wiring their homes up with Ethernet.

I've drawn a bit of a blank so far on net searches in this general
area, ie. PICs in Ethernet-related applications.  If anyone has come
across any such, or has ideas on how PICs might handle fast networking
simply (full IP stack not required!), I'd love to hear about it.

Cheers,

Rich.