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Re: Linux embedded and direction control of RS485 transceiver

From upsidedown@downunder.com
Newsgroups comp.arch.embedded
Subject Re: Linux embedded and direction control of RS485 transceiver
Message-ID <ql7o5g91qbihbbm8q2b45485eb46jcaq7t@4ax.com> (permalink)
References (2 earlier) <s3fe6a$khm$1@dont-email.me> <94km5g9h8l37mqgtm6ukbjq685ncr1oor6@4ax.com> <s3fpj4$87s$1@dont-email.me> <d9sm5gps2khlp989rnm0n71ce1m97rjfd0@4ax.com> <s3g1ao$73d$1@dont-email.me>
Date 2021-03-25 07:34 +0200
Organization Elisa Customer

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On Wed, 24 Mar 2021 19:44:39 +0100, David Brown
<david.brown@hesbynett.no> wrote:

>On 24/03/2021 18:22, upsidedown@downunder.com wrote:
>> On Wed, 24 Mar 2021 18:32:36 +0200, Tauno Voipio
>> <tauno.voipio@notused.fi.invalid> wrote:
>> 
>
>>> The Modbus RTU is rotten - a protocol so badly designed that it
>>> is difficult to exceed. Modbus on TCP is no better.
>> 
>> What is wrong with Modbus/TCP ? It is a nice request/response protocol
>> with a fixed size header (including byte count) and variable size
>> payload ?
>> 
>> 
>
>Modbus/TCP has a bit of redundancy in its headers, and some limits that
>exist only because of its heritage (like the maximum number of registers
>you are allowed to transfer at a time being 127, and the highest
>register address being 9999).  If you are writing your own server code,
>you can easily ignore them, but the master side has to know that the
>server supports them.

In the human readable format, e.g. the "4" format (40001 .. 49999)
seem to imply only 9999 holding registers, but the 4 in the address is
not usually transmitted, only 0 .. 9998 in the message. However, you
can put 0000h to FFFFh in the message field. It is just the human
readable form that has problems. Some use 499999 or 4'99999. Very old
implementation used 4001 to 4999 for the human readable format.

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Thread

Linux embedded and direction control of RS485 transceiver pozz <pozzugno@gmail.com> - 2021-03-24 00:06 +0100
  Re: Linux embedded and direction control of RS485 transceiver upsidedown@downunder.com - 2021-03-24 07:28 +0200
    Re: Linux embedded and direction control of RS485 transceiver Don Y <blockedofcourse@foo.invalid> - 2021-03-24 06:17 -0700
      Re: Linux embedded and direction control of RS485 transceiver upsidedown@downunder.com - 2021-03-24 17:49 +0200
        Re: Linux embedded and direction control of RS485 transceiver Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2021-03-24 18:32 +0200
          Re: Linux embedded and direction control of RS485 transceiver upsidedown@downunder.com - 2021-03-24 19:22 +0200
            Re: Linux embedded and direction control of RS485 transceiver David Brown <david.brown@hesbynett.no> - 2021-03-24 19:44 +0100
              Re: Linux embedded and direction control of RS485 transceiver upsidedown@downunder.com - 2021-03-25 07:34 +0200
              Re: Linux embedded and direction control of RS485 transceiver upsidedown@downunder.com - 2021-03-25 07:47 +0200
            Re: Linux embedded and direction control of RS485 transceiver Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2021-03-24 21:13 +0200
              Re: Linux embedded and direction control of RS485 transceiver upsidedown@downunder.com - 2021-03-25 07:39 +0200
              Re: Linux embedded and direction control of RS485 transceiver David Brown <david.brown@hesbynett.no> - 2021-03-25 10:48 +0100
                Re: Linux embedded and direction control of RS485 transceiver Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2021-03-25 16:33 +0200
                Re: Linux embedded and direction control of RS485 transceiver Grant Edwards <invalid@invalid.invalid> - 2021-03-25 14:49 +0000
                Re: Linux embedded and direction control of RS485 transceiver upsidedown@downunder.com - 2021-03-25 18:43 +0200
                Re: Linux embedded and direction control of RS485 transceiver David Brown <david.brown@hesbynett.no> - 2021-03-26 09:47 +0100
        Re: Linux embedded and direction control of RS485 transceiver Don Y <blockedofcourse@foo.invalid> - 2021-03-24 14:30 -0700
  Re: Linux embedded and direction control of RS485 transceiver dalai lamah <antonio12358@hotmail.com> - 2021-03-24 11:48 +0100
    Re: Linux embedded and direction control of RS485 transceiver pozz <pozzugno@gmail.com> - 2021-03-25 00:23 +0100
  Re: Linux embedded and direction control of RS485 transceiver "A.P.Richelieu" <aprichelieu@gmail.com> - 2021-05-09 13:24 +0200
    Re: Linux embedded and direction control of RS485 transceiver Uwe Bonnes <bon@hertz.ikp.physik.tu-darmstadt.de> - 2021-05-09 12:01 +0000
    Re: Linux embedded and direction control of RS485 transceiver pozz <pozzugno@gmail.com> - 2021-05-10 09:46 +0200

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