🚀 go-pugleaf

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.
| Our goal is to have data exchanged between a host cpu and any number of
| ( well ok, 8 :) attached slave devices. ... Any help (even remote references
| from 15 years ago) would be most welcome.
+---------------

Well, 15-year-old stuff (or 20-yr-old) is indeed where you should look! ;-}

Many "ancient" serial protocols allowed multi-drop: BSC ("BiSync"), SDLC,
DDCMP, to name just a few. And the phone company provided leased lines
in multi-dropped configurations. It was quite common to have a central
location in, say, Chicago, with a multi-drop line that hit Kansas City,
Dallas, Abilene, and another one that hit Atlanta, Jacksonville, Miami, &c.

As far back as 1973 or -4, at Dig. Comm. Assoc. we were shipping statistical
multiplexers that could multi-drop off a single sync phone line (e.g., using
Bell 208 or 209 modems). That is, each multi-dropped mux could have multiple
local terminals, all running to the same host via a "head end" mux. The muxes
used our own implementation of DEC's DDCMP as the link-layer protocol (as
we'd call it today), but if I did it again today, I'd probably use HDLC (only
because so few current programmers are familiar with DDCMP, which is really
quite nice).


-Rob

-----
Rob Warnock, MS-9U/510		rpw3@sgi.com
Silicon Graphics, Inc.		(415)390-1673
2011 N. Shoreline Blvd.
Mountain View, CA  94043