"Dr. Rich Artym" <rartym@GALACTA.DEMON.CO.UK> wrote:
> 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.)

Rich Ottosen and I have discussed this from time to time.  Even running the
PIC at the maximum rated speed, the amount of external hardware needed to
provide hardware assist for Ethernet will cost more than a complete
Ethernet chip.  The receive side is the more difficult, and requires a PLL
for clock recovery and a Manchester decoder, in addition to a shift register.
The bit stuffing could potentially be done in software.

A simple Ethernet chip like the Crystal Semiconductor CS8900 is very
inexpensive and does not require many other components.  It has enough
internal memory for two Ethernet frames, and the host interface is simple.
It should be possible to use this with a PIC to implement a simple network
node.

Even with the Scenix part in turbo mode at 50 MHz (20 nS per instruction),
Ethernet would still require substantial external support hardware if a
standard Ethernet chip was not used.

SMC also makes a simple Ethernet chip like the CS8900, but I don't know the
part number.

Cheers,
Eric