Date   : Wed, 17 Feb 1993 19:57:57 +0100
From   : stjohn@... (Chris StJohn)
Subject: Re: Cheapo network

I agree that flat-out you can get very high bandwidth (though I must say I'm
impressed that the olde wurlde tech. in the beebs can manage nearly 80Kbaud)
The trouble is that if you start playing with that sort of speed in a network
application you need a 100us interrupt cycle (remember that you're going to
want to do something with the machine at the same time as being on the net!)
you're doing well if you can get a 400us cycle out of a 6502 and even that
will need a lot of bitdiddling if you're going to have a workable system.

As for coax, I would have thought that above about 10kbaud you're better off
with screening. The company I was working for was Sollac, the largest steel
production outfit in Europe. The net was supposed to work next to electric
arc welders ;-) as it was to help control a steel rolling plant.

Anyway, somewhere I have all the sources for what I wrote. I'll try to dig
'em up. I would have thought that a cheap net would either be a Cambridge
Rind style system or else a Cheaponet (in fact if you hunt around in old
digi-electronics tutorial books they often have a cheap ethernet near the
end. I think there are chips around but we're getting off the subject...)
If the beeb ACIA can do simultaneous I/O (which I think it can as I remember
testing mine by wiring out to in) then you have a chance of an ethernet
protocol which is dead easy to code. Otherwise it's a ring system which is
harder but not much.

Don't underestimate the speed problem. I was using a 486 at Sollac and we
had to install special device drivers to get 95% efficiency (after framing
& CRC) at 19k2. Does anyone know how Econet work(ed/s) ??

  ,--,             Chris StJohn, LIX, Ecole Polytechnique, 91128
 /    /_  __' _    Palaiseau, Cedex, FRANCE. (+33) 1.69.33.45.93
(____/ (_/ (_/_).
                    said 'Cousot' and everything became top"