Re: Shared Communications Bus - RS-422 or RS-485

From	chris <chris-nospam@tridac.net>
Newsgroups	comp.arch.embedded
Subject	Re: Shared Communications Bus - RS-422 or RS-485
Date	2022-11-05 00:13 +0000
Organization	Aioe.org NNTP Server
Message-ID	<tk49r0$156q$1@gioia.aioe.org> (permalink)
References	<6b8c6b92-a2ca-4849-ba68-f03060bc41fcn@googlegroups.com>

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On 11/2/22 05:28, Rick C wrote:
> I have a test fixture that uses RS-232 to communicate with a PC.  It actually uses the voltage levels of RS-232, even though this is from a USB cable on the PC, so it's only RS-232 for maybe four inches.  lol
> 
> I'm redesigning the test fixtures to hold more units and fully automate a few features that presently requires an operator.  There will now be 8 UUTs on each test fixture and I expect to have 10 to 20 test fixtures in a card rack.  That's 80 to 160 UUTs total.  There will be an FPGA controlling each pair of UUTs, so 80 FPGAs in total that the PC needs to talk to.
> 
> Rather than working on a way to mux 80 RS-232 interfaces, I'm thinking it would be better to either daisy chain, or connect in parallel all these devices.  The protocol is master-slave where the master sends a command and the slaves are idle until they reply.  The four FPGAs on a test fixture board could be connected in parallel easily enough.  But I don't think I want to run TTL level signals between so many boards.
> 
> I could do an RS-422 interface with a master to slave pair and a slave to master pair.  The slaves do not speak until spoken to, so there will be no collisions.
> 
> RS-485 would allow all this to be over a single pair of wires.  But the one big issue I see people complain about is getting PC software to not clobber the slaves, or I should say, to get the master to wait long enough that it's not clobbering it's own start bit by overwriting the stop bit of the slave.  I suppose someone, somewhere has dealt with this on the PC and has a solution that doesn't impact bus speed.  I run the single test fixture version of this at about 100 kbps.  I'm going to want as much speed as I can get for 80 FPGAs controlling 160 UUTs.  Maybe I should give that some analysis, because this might not be true.
> 
> The tests are of two types, most of them are setting up a state and reading a signal.  This can go pretty fast and doesn't take too many commands.  Then there are the audio tests where the FPGA sends digital data to the UUT, which does it's thing and returns digital data which is crunched by the FPGA.  This takes some small number of seconds and presently the protocol is to poll the status until it is done.  That's a lot of messages, but it's not necessarily a slow point.  The same test can be started on every UUT in parallel, so the waiting is in parallel.  So maybe the serial port won't need to be any faster.
> 
> Still, I want to use RS-422 or RS-485 to deal with ground noise since this will be spread over multiple boards that don't have terribly solid grounds, just the power cable really.
> 
> I'm thinking out loud here as much as anything.  I intended to simply ask if anyone had experience with RS-485 that would be helpful.  Running two wires rather than eight would be a help.  I'll probably use a 10 pin connector just to be on the safe side, allowing the transceivers to be used either way.
> 

I worked on highway traffic sign project some years back that used
multidrop RS423. The sign driven from a roadside controller, with a
supervisory controller between that and led column controllers.
Supervisory controller always master, with col controllers slaves.
Master always initiated comms, with col controllers talking when
addressed. A simple software state machine and line turnaround for
the selected column to talk. Used diff line transceivers at the tx
and rx ends, which could be tristated at the output. Interesting
project and with a 15 yr design life, probably hundreds still
working now. RS423 multidrop works well, though don't remember what
the max supported speeds are. Much cheaper than network, but you can
used standard cat5 etc network cables and pcb sockets to tie it all
together...

Chris

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Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-01 22:28 -0700
  Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-02 10:28 +0100
    Re: Shared Communications Bus - RS-422 or RS-485 pozz <pozzugno@gmail.com> - 2022-11-02 11:54 +0100
      Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-02 14:27 +0100
    Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-02 12:20 -0700
      Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-02 21:49 +0100
        Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-02 16:27 -0700
          Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-03 12:42 +0100
            Re: Shared Communications Bus - RS-422 or RS-485 pozz <pozzugno@gmail.com> - 2022-11-03 14:00 +0100
              Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-03 16:26 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 pozz <pozzugno@gmail.com> - 2022-11-04 08:45 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-04 10:49 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 pozz <pozzugno@gmail.com> - 2022-11-04 15:37 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-04 17:36 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-04 10:11 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-05 11:58 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-05 09:55 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 11:00 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-07 15:46 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 08:05 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-07 19:02 -0500
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 17:15 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-08 06:54 -0500
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-08 05:50 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Clifford Heath <no_spam@please.net> - 2022-11-09 10:45 +1100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-08 16:46 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Clifford Heath <no_spam@please.net> - 2022-11-09 22:32 +1100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-09 04:53 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-09 23:45 -0500
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-09 21:42 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-04 08:40 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 antispam@math.uni.wroc.pl - 2022-11-04 22:53 +0000
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-04 18:07 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 antispam@math.uni.wroc.pl - 2022-11-05 03:46 +0000
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-05 02:09 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 10:40 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-05 12:47 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-05 10:23 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-05 19:57 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-05 13:42 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-06 11:55 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-06 05:56 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-06 21:53 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 01:58 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 11:26 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 02:39 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 12:07 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 08:25 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 17:57 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 09:50 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 21:30 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 14:27 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-08 00:07 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 16:50 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-08 09:02 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-08 06:58 -0500
                Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-06 18:34 -0500
                Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-06 15:37 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-06 19:18 -0500
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 02:07 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 02:03 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 11:55 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 08:18 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 18:20 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 10:26 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Stef <me@this.is.invalid> - 2022-11-07 22:04 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 14:54 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-07 15:14 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 16:57 -0800
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-07 07:51 -0800
              Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 08:29 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 10:36 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 12:32 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 13:08 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 13:40 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 16:50 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 21:10 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-04 11:13 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-04 08:52 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-04 20:03 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-05 17:25 +0100
                Re: Shared Communications Bus - RS-422 or RS-485 David Brown <david.brown@hesbynett.no> - 2022-11-04 11:01 +0100
  Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-02 15:00 -0700
    Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-02 16:31 -0700
      Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-02 17:36 -0700
        Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-02 21:58 -0700
          Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 09:57 -0700
            Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 12:02 -0700
              Re: Shared Communications Bus - RS-422 or RS-485 Paul Rubin <no.email@nospam.invalid> - 2022-11-03 12:53 -0700
                Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 13:33 -0700
  Re: Shared Communications Bus - RS-422 or RS-485 Dave Nadler <drn@nadler.com> - 2022-11-03 15:37 -0400
    Re: Shared Communications Bus - RS-422 or RS-485 Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-03 13:32 -0700
      Re: Shared Communications Bus - RS-422 or RS-485 Richard Damon <Richard@Damon-Family.org> - 2022-11-04 22:47 -0400
  Re: Shared Communications Bus - RS-422 or RS-485 chris <chris-nospam@tridac.net> - 2022-11-05 00:13 +0000

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