Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.arch.embedded > #30378

Re: Multi-master RS485

Show all headers | View raw

Il 25/03/2021 17:33, Don Y ha scritto:
> On 3/25/2021 9:27 AM, pozz wrote:
>> Are there any *real* implementation of multi-master half-duplex RS485 
>> bus?
>>
>> I often use half-duplex RS485 and I always use a master-slave polling 
>> protocol. This choice dramatically reduce the complexity of the system 
>> and it works well with a limited number of nodes.
>>
>> When the nodes are 10 or 20 and they usually send only a few bytes in 
>> a minuted, the polling scheme is inefficient. The bus is alway busy 
>> for polling, but the real data are very small.
>>
>> I'm thinking to "improve" this bus with a multi-master approach, but 
>> it doesn't appear simple. Do you know of real and working 
>> implementation of this type on half-duplex RS485 bus?
> 
> Sure!  An easy way is to time-division-multiplex the bus and assign
> specific slots to specific nodes.

This means assigning a predefined slot duration for each node. What 
happens if a node wants to transmit a big packet? It should split packet 
in multiple consecutive slots.

Moreover, is time-division-multiplex efficient? Now with master-slave 
polling mechanism I already have a time-division-multiplex: for each 
slave there's a time window in which master sends the token and slave 
reply with token (and probably data).
With a pure time-division-multiplex I will save only the time of the 
master request.


> 
> You can also use a token-passing protocol to select the next master.

Same, each node is an "active" node in every loop. I imagine a bus that 
is idle for most of the time and busy only when a node wants to transmit 
something.
In my case real data are very low. Anyway I have to face the event of a 
conflict.


> 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.

This is why I'm searching a "ready-to-use" protocol, if any.


> 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]

Back to comp.arch.embedded | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web