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Re: Multi-master RS485

From David Brown <david.brown@hesbynett.no>
Newsgroups comp.arch.embedded
Subject Re: Multi-master RS485
Date 2021-03-25 20:28 +0100
Organization A noiseless patient Spider
Message-ID <s3io8l$5ff$1@dont-email.me> (permalink)
References <s3idlk$dm7$1@dont-email.me> <s3ie0u$ldm$1@dont-email.me> <s3iead$p3k$1@reader1.panix.com>

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On 25/03/2021 17:38, Grant Edwards wrote:
> On 2021-03-25, Don Y <blockedofcourse@foo.invalid> wrote:
>> On 3/25/2021 9:27 AM, pozz wrote:
> 
>>> Are there any *real* implementation of multi-master half-duplex RS485 bus?
> 
>> Sure!  An easy way is to time-division-multiplex the bus and assign
>> specific slots to specific nodes.
>>
>> You can also use a token-passing protocol to select the next master.
>>
>> You have to address start-up issues to initialize the first
>> set of accesses.  And, you have to include provisions to handle
>> the case where things go wonky and resynchronization becomes
>> necessary.
>>
>> But, you *can* handle things like a device failing to pass the token
>> or skipping its timeslot in the "normal" protocol.
>>
>> Note that any approach requires pre-configuration; you can't just
>> arbitrarily add nodes to the bus and expect them to arbitrate
>> access (like CD/MA).
>>
>> [This is a minor lie -- but, autoconfiguration is not trivial]
> 
> Since the OP didn't specify async UARTs, I might mention that you can
> CAN controllers with a half-duplex RS485 physical layer but it's a bit
> of hack and easier to just use real CAN transceivers.
> 

The first CAN transceivers were basically RS-485 transceivers with the
CAN TX line connected to the driver's transmit enable input, the
driver's receive enable always on, and the driver's data in line
connected to 0.

You can also use UARTs along with CAN transceivers.  (I worked with a
propriety protocol like that a good while ago - it was a slightly odd
bus that evolved gradually from a Dallas one-wire bus.)

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Thread

Multi-master RS485 pozz <pozzugno@gmail.com> - 2021-03-25 17:27 +0100
  Re: Multi-master RS485 Don Y <blockedofcourse@foo.invalid> - 2021-03-25 09:33 -0700
    Re: Multi-master RS485 Grant Edwards <invalid@invalid.invalid> - 2021-03-25 16:38 +0000
      Re: Multi-master RS485 Don Y <blockedofcourse@foo.invalid> - 2021-03-25 09:57 -0700
      Re: Multi-master RS485 David Brown <david.brown@hesbynett.no> - 2021-03-25 20:28 +0100
    Re: Multi-master RS485 pozz <pozzugno@gmail.com> - 2021-03-25 17:57 +0100
      Re: Multi-master RS485 Don Y <blockedofcourse@foo.invalid> - 2021-03-25 10:04 -0700
  Re: Multi-master RS485 upsidedown@downunder.com - 2021-03-25 19:02 +0200
  Re: Multi-master RS485 antispam@math.uni.wroc.pl - 2021-03-26 15:54 +0000
    Re: Multi-master RS485 pozz <pozzugno@gmail.com> - 2021-03-28 00:37 +0100
      Re: Multi-master RS485 Richard Damon <Richard@Damon-Family.org> - 2021-03-27 20:14 -0400
        Re: Multi-master RS485 upsidedown@downunder.com - 2021-03-28 07:32 +0300
          Re: Multi-master RS485 Richard Damon <Richard@Damon-Family.org> - 2021-03-28 07:20 -0400
            Re: Multi-master RS485 upsidedown@downunder.com - 2021-03-28 14:59 +0300
              Re: Multi-master RS485 Richard Damon <Richard@Damon-Family.org> - 2021-03-28 08:09 -0400
      Re: Multi-master RS485 antispam@math.uni.wroc.pl - 2021-03-28 02:01 +0000
      Re: Multi-master RS485 Don Y <blockedofcourse@foo.invalid> - 2021-03-27 19:57 -0700
      Re: Multi-master RS485 Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2021-03-28 15:52 +0200
        Re: Multi-master RS485 Richard Damon <Richard@Damon-Family.org> - 2021-03-28 13:06 -0400
      Re: Multi-master RS485 pozz <pozzugno@gmail.com> - 2021-03-31 00:34 +0200
        Re: Multi-master RS485 Don Y <blockedofcourse@foo.invalid> - 2021-03-30 18:51 -0700
        Re: Multi-master RS485 upsidedown@downunder.com - 2021-03-31 06:42 +0300
          Re: Multi-master RS485 Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2021-03-31 09:50 +0200
        Re: Multi-master RS485 David Brown <david.brown@hesbynett.no> - 2021-03-31 10:23 +0200
          Re: Multi-master RS485 pozz <pozzugno@gmail.com> - 2021-03-31 12:27 +0200
            Re: Multi-master RS485 David Brown <david.brown@hesbynett.no> - 2021-03-31 14:43 +0200
          Re: Multi-master RS485 pozz <pozzugno@gmail.com> - 2021-03-31 13:39 +0200
            Re: Multi-master RS485 David Brown <david.brown@hesbynett.no> - 2021-03-31 14:46 +0200
            Re: Multi-master RS485 Don Y <blockedofcourse@foo.invalid> - 2021-03-31 06:20 -0700
          Re: Multi-master RS485 upsidedown@downunder.com - 2021-03-31 15:29 +0300
            Re: Multi-master RS485 David Brown <david.brown@hesbynett.no> - 2021-03-31 14:49 +0200

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