Date   : Mon, 15 Feb 1993 21:36:32 +0100
From   : stjohn@... (Chris StJohn)
Subject: Cheapo network

Yeah. Multidrop networks on RS232 work 'cos I implemented a protocol called
ModBus(tm) on a PC while working last summer. With suitable device handlers
(ie. with fast interrupt capability) you can get full 19200 baud (though I
think we needed coax cables :-)
The hardest bit (and most painful from a hobbyist point of view) is that the
protocol assumed that one machine was dedicated to allocating bandwidth to
the others. Fine if you have a spare beeb! A long time ago I designed a
protocol (this was 5th year secondary...) which didn't need a master but
instead the machines pass on a key around a ring. Trouble was that you
had to reconfigure the network to add/subtract a machine. If anyone is
interested in any of this, drop me a line and I'll describe more fully
what I did.

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

PS: still racking my brains about who the (tm) of ModBus belongs to. Gould
rings a bell but I wouldn't put a beer on it. Anyway, here in France
there isn't another user in a 200 mile radius so I think you can count
me out on this one...