🚀 go-pugleaf

In <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.  You need the RS-485 protocol
| to multi-drop devices, because it lets the line float if a device
| has nothing to say.  There are 232 to 485 converters available (or
| there were 7 years ago).  Then you can implement a master-slave
| software protocol for the universe of devices attached to the line.
| 
| In ISO terms, RS-232/485 is barely a physical layer specification.
| You get to do anything you want with the rest of the layers.

Wyse makes (made?) both 485 terminals, and 485 drops to rs232 protocol
boxes (2 and 8 232 ports per box).  I don't remember if they ever made
the controller boards.  This was done about 5 years back, originally as
a joint project with Altos.  I did a lot of the driver work, and it
worked pretty well (we ran 64 terminals at full speed both directions
off a 286 box).  As I recall, the datarate was about 1.4 Mbits/sec on
the multidrop wire. 
--
Let no one tell me that silence gives consent,  |   Dave Olson
because whoever is silent dissents.             |   Silicon Graphics, Inc.
    Maria Isabel Barreno                        |   olson@sgi.com