🚀 go-pugleaf

In article 26423@seachg.uucp, burke@seachg.uucp (Michael Burke) writes:
> In article <1993Jan24.181433.26225@rosevax.rosemount.com> bill@texan.rosemount.com (William Hawkins) writes:
> >>jdc@isis.cs.wayne.edu (Jon Cardwell) writes:
> >>+---------------
> >>| We're looking for sources or references for a "multi-drop serial protocol"
> >>| i.e. one that allows multiple devices to be attached to the same serial line.
> >
> >RS-232 is not a multi-drop protocol *electrically* because it holds
> >the line at the mark (or space) state.  
> 
> Hogwash...
> 
> RS232 has been used for years with BSC 3270 multi-drop circuits. Generally,
> the trick is to use the fastest modem turn around time possible to get best
> results. The "poll-ack" protocols are above this physical standard.
> 
> Remember, multi-drop does not mean a "bus architecture" in the strictest
> sense. One orders a multi-drop circuit from the Telco. I have not been
> involved with BSC 3270 circuits for many years (about 15) so I have no idea
> how one would go about building an in-house multi-drop circuit....
> 
> 
> -- 
> ---
> Michael Burke
> 
> Sea Change Corporation
> 6695 Millcreek Drive, Unit 8 
> Mississauga, Ontario, Canada L5N 5R8
> Tel: 416-542-9484  Fax: 416-542-9479
> UUCP: ...!uunet!uunet.ca!seachg!burke

The easiest way of building such a circuit is to use a central modem 
(constant carrier), an analog bridge (with n+1 ports, where n is the
number of remote stations), and n number of 4-wire modems at the far
end (SWITCHED carrier).  The remote stations would need to assert the
Request-to-Send lead in order to transmit.  The use of 4-wire circuits
and the proper modems ( with short RTS-CTS delays) will result in a 
decent system.  We do this routinely for alarm transponder circuits.

	- John

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