OK, so we can't expect Cisco-type performance and full IP networking all
    done within a PIC, but it's certainly able to do frame decoding and
    encoding offline and to hand frames to fast but cheap external hardware
    for delivery at Ethernet rates.

Thanks for the plug.

Ethernet "controllers" come in approximately three flavors:

1) full-feature high speed controllers with built-in DMA and/or bus
   controllers  (ie AMD LANCE.)

2) byte-delivery devices with only a FIFO (ie SEEQ 8003.)  As used in
   several generations of cisco routers (with external microprogrammed
   bitslice to do everything in (1), plus additional stuff.

3) ISA-PC oriented controllers with independent buffer memory (National
   8390x series and "reference design".

The last of these is most suited to front-ending a PIC, I think.  The
orignal design was for ISA 8bit slots which are also too slow to
actually handle ethernet speed traffic, so the PC would stuff data off
into an 8k buffera and then say "go", and vis-versa.  An extra data copy
(evil stuff for a high speed router), but just the thing for slow
processors.

The integration rate has stepped up, of course, and now the single chip
controllers contain built-in 10baseT tranceivers, IEEE802.mumble
compatible network managment capabilities, etc, etc, but you can easilly
find 8bit ethernet cards based on the original 8390 ("Novell type 1", I
think) for less than $20 (unused), now that everyone wants PCI, 100Mbps,
and so on...

Note that without built-in 10baseT or thinnet tranceivers, you may be
paying nearly as much to connect a plain ethernet card to your net as
you would for an rs232 port into one of the cheaper (non-cisco :-)
ethernet terminal servers (10baseT external xceiver, some fraction of a
hub box, etc.)

BillW
cisco