🚀 go-pugleaf

In article <1992Sep15.150015.7409@sbctri.sbc.com>, tadams@sbctri.sbc.com (Tom. Adams 529-7860) writes:
> I was wasting time in a meeting, and came up with an idea that seems
> interesting to me.  Consequently I'm sure it's been done, or more likely
> been shown to be just incredibly stupid. :)
> 
> I'd like to connect multiple devices to an RS232 line, buswise.  All devices
> would either be programable, (i.e. PC's) or be frontended by a (cheap)
> microprocessor.  I'm wondering if CSMA/CD is a reasonable way to manage 
> very low speed bus contention.  If so, it would seem reasonable to transmit 
> address information, data, CRC's etc over the wire.  I'm not quite sure
> how to manage the Collision detect part, since I can't just look at 
> voltage levels on the wire.  Applications would be low volume data logging
> and control systems, ridiculously overpriced burglar alarms, etc.
> 
> Perhaps it would be more reasonable to just look at some twisted pair
> protocol that already has multi drop, like sdlc.
> 
> Opinions?


I think there was an article on that in Byte many years ago, one of the
Circuit Cellar series. It was a cheap multi-drop network using RS232
and a handful of diodes. You could try Byte backissues from the
early 80's, sorry I can't pin it down more precisely :-)

Collision detect was pretty simple, if I remember correctly the network
simply linked the Tx and Rx through diodes, and each device watched what it
sent coming back in through its receive line. If it didn't match, there
had been a collision & it backed-off & retried.


Steve

-- 
Steve McKinty
SUN Microsystems ICNC
38240 Meylan, France
email: smckinty@france.sun.com	   BIX: smckinty