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

From	pozz <pozzugno@gmail.com>
Newsgroups	comp.arch.embedded
Subject	Re: Shared Communications Bus - RS-422 or RS-485
Date	2022-11-03 14:00 +0100
Organization	A noiseless patient Spider
Message-ID	<tk0e27$1f1rv$1@dont-email.me> (permalink)
References	(1 earlier) <tjtd7g$145er$1@dont-email.me> <b4a93d7d-3d6f-4b23-86b1-f1066b6b72ebn@googlegroups.com> <tjul46$18dkn$3@dont-email.me> <ec91ddbe-6777-494f-8001-cf57fc15deeen@googlegroups.com> <tk09ev$1f0de$1@dont-email.me>

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Il 03/11/2022 12:42, David Brown ha scritto:
> On 03/11/2022 00:27, Rick C wrote:
>> On Wednesday, November 2, 2022 at 4:49:16 PM UTC-4, David Brown wrote:
>>> On 02/11/2022 20:20, Rick C wrote:
>>>> On Wednesday, November 2, 2022 at 5:28:21 AM UTC-4, David Brown
>>>> wrote:
>>>>> On 02/11/2022 06:28, Rick C wrote:

> You are correct that reception is in the middle of the stop bit 
> (typically sub-slot 9 of 16).  The first transmitter will be disabled at 
> the end of the stop bit, and the next transmitter must not enable its 
> driver until after that point - it must wait at least half a bit time 
> after reception before starting transmission.  (It can wait longer 
> without trouble, which is why faster baud rates are less likely to 
> involve any complications here.)

Do you mean that RX interrupt triggers in the middle of the stop bit and 
not at the end? Interesting, but are you sure this is the case for every 
UART implemented in MCUs?

I wouldn't be surprised if the implementation was different for 
different manufacturers.

>> None of this matters to me really.  I'm going to use more wires, and 
>> do the multi-drop from the PC to the slaves on one pair and use RS-422 
>> to multi-point from the slaves to the PC.  Since the slaves are 
>> controlled by the master, they will never collide.  The master can't 
>> collide with itself, so I can ignore any issues with this.  I will use 
>> the bias resistors to assure a valid idle state.  I may need to select 
>> different devices than the ones I use in the product.  I think there 
>> are differences in the input load and I want to be sure I can chain up 
>> to 32 units.
>>
> 
> OK.  I have no idea what such a hybrid bus should technically be called, 
> but I think it should work absolutely fine for the purpose and seems 
> like a solid solution.  I would not foresee any issues with 32 nodes on 
> such a bus, especially if it is relatively short and you have 
> terminators at each end.

In my experience, termination resistors at each end of the line could 
introduce other troubles if they aren't strictly required (because of 
signal integrity on long lines at high baud rates).

The receiver input impedance of all the nodes on the bus are in parallel 
with the two terminators. If you have many nodes, the equivalent 
impedance on the bus is much small and the partition with bias resistors 
could reduce the differential voltage between A and B at idle to less 
than 200mV.

If you don't use true fail-safe transceivers, a fault start bit could be 
seen by these kind of receivers.

Thread

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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