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Re: Two-wires RS485 and the driver enable problem

From Grant Edwards <invalid@invalid.invalid>
Newsgroups comp.arch.embedded
Subject Re: Two-wires RS485 and the driver enable problem
Date 2014-10-13 19:09 +0000
Organization PANIX Public Access Internet and UNIX, NYC
Message-ID <m1h817$l7m$2@reader1.panix.com> (permalink)
References <m1geor$bt4$1@dont-email.me> <os7o3adm5pfb61gnegh1roc0sktrsgfs97@4ax.com>

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On 2014-10-13, upsidedown@downunder.com <upsidedown@downunder.com> wrote:

> You must be quite desperate, if you intend to use 1x550 style chips on
> RS-485 :-). That chip family is useless for any high speed half duplex
> communication.
>
> You can get an interrupt when you load the last character into the Tx
> shift register, but you can't get an interrupt, when the last bit of
> the last character is actually shifted out of the Tx shift register.
>
> In real word, some high priority code will have to poll, when the
> last bit of your transmission has actually sent the last stop bit of
> your last byte into the line.

And (in my experience) figuring out when that stop bit has been sent
can be problematic.  Not all '550 "compatible" UARTs wait until the
end of the stop bit to set the "transmit shift register empty" status
bit.  Some I've used set it as soon as the last data bit has been
sent, and if you turn of the driver at that point, you canse lose the
stop bit and create a framing error.

-- 
Grant Edwards               grant.b.edwards        Yow! My polyvinyl cowboy
                                  at               wallet was made in Hong
                              gmail.com            Kong by Montgomery Clift!

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Thread

Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-13 13:58 +0200
  Re: Two-wires RS485 and the driver enable problem Wouter van Ooijen <wouter@voti.nl> - 2014-10-13 14:29 +0200
    Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-13 14:38 +0200
      Re: Two-wires RS485 and the driver enable problem Wouter van Ooijen <wouter@voti.nl> - 2014-10-13 15:28 +0200
        Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-13 07:21 -0700
          Re: Two-wires RS485 and the driver enable problem Wouter van Ooijen <wouter@voti.nl> - 2014-10-13 16:46 +0200
            Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-13 08:02 -0700
        Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-13 16:59 +0200
          Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-13 08:08 -0700
            Re: Two-wires RS485 and the driver enable problem pozz <pozzugno@gmail.com> - 2014-10-14 07:48 +0200
              Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-13 23:28 -0700
                Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-14 09:20 +0200
                Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-14 06:09 -0700
              Re: Two-wires RS485 and the driver enable problem David Brown <david.brown@hesbynett.no> - 2014-10-14 10:36 +0200
          Re: Two-wires RS485 and the driver enable problem Wouter van Ooijen <wouter@voti.nl> - 2014-10-13 18:14 +0200
      Re: Two-wires RS485 and the driver enable problem Tim Wescott <seemywebsite@myfooter.really> - 2014-10-13 16:30 -0500
  Re: Two-wires RS485 and the driver enable problem David Brown <david.brown@hesbynett.no> - 2014-10-13 14:47 +0200
    Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-13 14:56 +0200
      Re: Two-wires RS485 and the driver enable problem David Brown <david.brown@hesbynett.no> - 2014-10-13 16:13 +0200
      Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-13 08:06 -0700
        Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-14 08:50 +0200
          Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-14 14:34 -0700
  Re: Two-wires RS485 and the driver enable problem Richard Damon <Richard@Damon-Family.org> - 2014-10-13 09:11 -0400
  Re: Two-wires RS485 and the driver enable problem rickman <gnuarm@gmail.com> - 2014-10-13 10:53 -0400
    Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-13 17:03 +0200
  Re: Two-wires RS485 and the driver enable problem Grant Edwards <invalid@invalid.invalid> - 2014-10-13 15:20 +0000
    Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-16 09:01 +0200
      Re: Two-wires RS485 and the driver enable problem Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2014-10-16 10:19 +0300
      Re: Two-wires RS485 and the driver enable problem rickman <gnuarm@gmail.com> - 2014-10-16 05:02 -0400
  Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-13 08:17 -0700
    Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-13 08:19 -0700
    Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-14 09:28 +0200
      Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-14 06:09 -0700
        Re: Two-wires RS485 and the driver enable problem rickman <gnuarm@gmail.com> - 2014-10-14 14:28 -0400
    Re: Two-wires RS485 and the driver enable problem rickman <gnuarm@gmail.com> - 2014-10-14 04:36 -0400
  Re: Two-wires RS485 and the driver enable problem Les Cargill <lcargill99@comcast.com> - 2014-10-13 12:35 -0500
    Re: Two-wires RS485 and the driver enable problem langwadt@fonz.dk - 2014-10-13 15:02 -0700
      Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-13 17:36 -0700
        Re: Two-wires RS485 and the driver enable problem Les Cargill <lcargill99@comcast.com> - 2014-10-13 21:53 -0500
          Re: Two-wires RS485 and the driver enable problem Don Y <this@is.not.me.com> - 2014-10-13 20:24 -0700
  Re: Two-wires RS485 and the driver enable problem upsidedown@downunder.com - 2014-10-13 22:02 +0300
    Re: Two-wires RS485 and the driver enable problem Grant Edwards <invalid@invalid.invalid> - 2014-10-13 19:09 +0000
      Re: Two-wires RS485 and the driver enable problem glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-10-13 20:58 +0000
        Re: Two-wires RS485 and the driver enable problem Grant Edwards <invalid@invalid.invalid> - 2014-10-13 21:08 +0000
          Re: Two-wires RS485 and the driver enable problem langwadt@fonz.dk - 2014-10-13 14:40 -0700
    Re: Two-wires RS485 and the driver enable problem Dave Nadler <drn@nadler.com> - 2014-10-14 09:58 -0700
      Re: Two-wires RS485 and the driver enable problem rickman <gnuarm@gmail.com> - 2014-10-14 14:20 -0400
        Re: Two-wires RS485 and the driver enable problem David Brown <david.brown@hesbynett.no> - 2014-10-14 23:35 +0200
          Re: Two-wires RS485 and the driver enable problem rickman <gnuarm@gmail.com> - 2014-10-15 02:00 -0400
            Re: Two-wires RS485 and the driver enable problem David Brown <david.brown@hesbynett.no> - 2014-10-15 09:47 +0200
              Re: Two-wires RS485 and the driver enable problem rickman <gnuarm@gmail.com> - 2014-10-16 01:30 -0400
                Re: Two-wires RS485 and the driver enable problem David Brown <david.brown@hesbynett.no> - 2014-10-16 20:46 +0200
                Re: Two-wires RS485 and the driver enable problem Dave Nadler <drn@nadler.com> - 2014-10-16 12:00 -0700
            Re: Two-wires RS485 and the driver enable problem upsidedown@downunder.com - 2014-10-15 11:01 +0300
            Re: Two-wires RS485 and the driver enable problem Grant Edwards <invalid@invalid.invalid> - 2014-10-15 14:24 +0000
              Re: Two-wires RS485 and the driver enable problem rickman <gnuarm@gmail.com> - 2014-10-16 01:17 -0400
                Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-16 08:36 +0200
                Re: Two-wires RS485 and the driver enable problem rickman <gnuarm@gmail.com> - 2014-10-16 05:05 -0400
                Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-16 12:54 +0200
                Re: Two-wires RS485 and the driver enable problem Grant Edwards <invalid@invalid.invalid> - 2014-10-16 14:16 +0000
    Re: Two-wires RS485 and the driver enable problem upsidedown@downunder.com - 2014-10-15 09:09 +0300
      Re: Two-wires RS485 and the driver enable problem Grant Edwards <invalid@invalid.invalid> - 2014-10-15 14:26 +0000
  Re: Two-wires RS485 and the driver enable problem glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-10-13 20:55 +0000
  Re: Two-wires RS485 and the driver enable problem Tim Wescott <seemywebsite@myfooter.really> - 2014-10-13 16:37 -0500
    Re: Two-wires RS485 and the driver enable problem pozzugno <pozzugno@gmail.com> - 2014-10-14 09:37 +0200
  Re: Two-wires RS485 and the driver enable problem Arlet Ottens <usenet+5@c-scape.nl> - 2014-10-14 20:44 +0200

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