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Groups > comp.arch.embedded > #31562

Re: Boxed MCU with RS-232 Port

From Andrew Smallshaw <andrews@sdf.org>
Newsgroups comp.arch.embedded
Subject Re: Boxed MCU with RS-232 Port
Date 2023-01-18 12:15 +0000
Organization A noiseless patient Spider
Message-ID <slrntsfonr.9sa.andrews@sdf.org> (permalink)
References (2 earlier) <af677448-3930-4c1f-b6da-afdba5720305n@googlegroups.com> <87cz7cvpi0.fsf@nightsong.com> <2b3941b6-1a59-412c-b088-29794ac047b3n@googlegroups.com> <878ri0vmvg.fsf@nightsong.com> <d5419959-247d-4162-9ae4-bdabfe1c7e01n@googlegroups.com>

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On 2023-01-17, Rick C <gnuarm.deletethisbit@gmail.com> wrote:
> On Tuesday, January 17, 2023 at 6:04:44 PM UTC-4, Paul Rubin wrote:
>> Gack, yeah. I had been thinking, this isn't my area, but my 
>> understanding is that the RS232 electrical spec requires voltages that 
>> are somewhat above TTL logic levels, and that various crappy devices 
>> skimp on these voltages and mostly work anyway. So that is a thing to 
>> suspect if a home-brew RS232 device is acting flaky. It could be that 
>> the device at the other end expects those voltages to be closer to the 
>> real spec.
>
> They used a MAX3232CPE which generates it's own voltages using
> switched capacitor voltage boost.  I wanted to check the values of
> the caps.  Seems the have different minimum values depending on
> the Vcc voltage.  But they are not in the BoM.  I'll ask about
> this.   It could easily be the cause of the problem.

That was my first thought as well so I looked it up to double check.
The MAX3232CPE is 0.1uF across the board so far as I can see.  You
do hit problems with MAX232's - the original needed 1uF caps but
the MAX232A and several alternate manufacturers specify 0.1uF as
a minimum.  Problems can arise if a MAX232 is put in place of one
of the alternatives but with the 3232 I'd expect people to get it
right.

OTOH the 3232 is a 3.3V compatible part.  One thing they all have
in common is the charge pumps are a bit weedy in terms of voltage,
aiming for +/-5.5V regardless of supply voltage.  That's within
current specs but the RS232 minimum voltages have dropped over the
years, I suppose it's possible the port of the receiver is an
older design.  In any case it doesn't leave particularly large
headroom for losses.  Do you know if the protocol translator is on
a 3.3v or 5v supply? If the latter a MAX232A (note the A) is a
drop-in replacement with typical +/-10V drive.  If 3.3V a booster
of some form will eliminate low voltage as an issue - in terms of
off the shelf hardware that would probably be a pair of RS232<>RS422
line extenders back to back.

-- 
Andrew Smallshaw
andrews@sdf.org

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Thread

Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-17 07:24 -0800
  Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-17 11:31 -0800
    Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-17 12:19 -0800
      Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-17 13:07 -0800
        Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-17 13:29 -0800
          Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-17 14:04 -0800
            Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-17 14:47 -0800
              Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-17 15:32 -0800
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-17 15:44 -0800
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-17 16:04 -0800
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-17 17:32 -0800
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-17 20:02 -0800
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-17 20:24 -0800
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-17 20:56 -0800
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-17 22:30 -0800
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-18 00:37 -0800
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-18 04:43 -0800
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-18 14:19 -0800
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-18 23:15 -0800
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-19 12:21 -0800
              Re: Boxed MCU with RS-232 Port Andrew Smallshaw <andrews@sdf.org> - 2023-01-18 12:15 +0000
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-18 04:55 -0800
                Re: Boxed MCU with RS-232 Port Andrew Smallshaw <andrews@sdf.org> - 2023-01-18 13:22 +0000
                Re: Boxed MCU with RS-232 Port Andrew Smallshaw <andrews@sdf.org> - 2023-01-18 13:28 +0000
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-18 06:20 -0800
      Re: Boxed MCU with RS-232 Port David Brown <david.brown@hesbynett.no> - 2023-01-18 10:04 +0100
  Re: Boxed MCU with RS-232 Port Theo <theom+news@chiark.greenend.org.uk> - 2023-01-18 16:18 +0000
    Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-18 14:10 -0800
      Re: Boxed MCU with RS-232 Port Theo <theom+news@chiark.greenend.org.uk> - 2023-01-19 10:29 +0000
        Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-01-19 05:41 -0700
          Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-19 10:00 -0800
            Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-19 12:42 -0800
              Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-19 14:10 -0800
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-19 16:16 -0800
        Re: Boxed MCU with RS-232 Port Grant Edwards <invalid@invalid.invalid> - 2023-01-19 16:07 +0000
          Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-19 10:13 -0800
          Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-01-19 14:51 -0700
        Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-19 10:06 -0800
          Re: Boxed MCU with RS-232 Port Theo <theom+news@chiark.greenend.org.uk> - 2023-01-20 13:03 +0000
            Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-20 06:28 -0800
            Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-01-20 19:14 -0800
              Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-01-20 20:41 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-01-21 05:05 -0700
              Re: Boxed MCU with RS-232 Port Theo <theom+news@chiark.greenend.org.uk> - 2023-01-21 10:53 +0000
          Re: Boxed MCU with RS-232 Port Herbert Kleebauer <klee@unibwm.de> - 2023-01-20 19:17 +0100
            Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-20 12:37 -0800
              Re: Boxed MCU with RS-232 Port Dimiter_Popoff <dp@tgi-sci.com> - 2023-01-20 23:02 +0200
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-20 14:08 -0800
                Re: Boxed MCU with RS-232 Port Dimiter_Popoff <dp@tgi-sci.com> - 2023-01-21 01:38 +0200
                Re: Boxed MCU with RS-232 Port antispam@math.uni.wroc.pl - 2023-01-21 01:58 +0000
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-20 18:44 -0800
                Re: Boxed MCU with RS-232 Port antispam@math.uni.wroc.pl - 2023-01-21 20:02 +0000
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-22 17:12 -0800
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-02-03 09:22 -0800
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-02-03 10:04 -0800
                Re: Boxed MCU with RS-232 Port Dimiter_Popoff <dp@tgi-sci.com> - 2023-03-26 22:24 +0300
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 02:27 -0700
  Re: Boxed MCU with RS-232 Port pozz <pozzugno@gmail.com> - 2023-01-20 08:54 +0100
    Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-20 01:03 -0800
  Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-22 12:18 -0700
    Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-03-22 20:35 -0700
      Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-22 23:26 -0700
        Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-22 23:28 -0700
          Re: Boxed MCU with RS-232 Port Theo <theom+news@chiark.greenend.org.uk> - 2023-03-23 10:06 +0000
            Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 00:59 -0700
          Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-03-23 09:00 -0700
            Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 01:03 -0700
        Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-03-23 08:54 -0700
          Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 01:02 -0700
            Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-03-24 01:43 -0700
            Re: Boxed MCU with RS-232 Port Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2023-03-24 12:44 +0100
              Re: Boxed MCU with RS-232 Port Theo <theom+news@chiark.greenend.org.uk> - 2023-03-24 14:20 +0000
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 08:08 -0700
                Re: Boxed MCU with RS-232 Port Theo <theom+news@chiark.greenend.org.uk> - 2023-03-24 16:23 +0000
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-03-24 13:42 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 14:31 -0700
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-03-24 18:19 -0700
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-03-24 18:22 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 18:34 -0700
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-03-24 19:43 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 20:01 -0700
                Re: Boxed MCU with RS-232 Port Paul Rubin <no.email@nospam.invalid> - 2023-03-24 21:18 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-24 15:35 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 18:21 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-24 19:21 -0700
                Re: Boxed MCU with RS-232 Port George Neuner <gneuner2@comcast.net> - 2023-03-25 21:42 -0400
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-25 19:26 -0700
                Re: Boxed MCU with RS-232 Port Jim Jackson <jj@franjam.org.uk> - 2023-03-26 18:27 +0000
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-26 13:23 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-26 13:32 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-26 13:52 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-26 19:30 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-26 20:31 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 07:04 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 09:21 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 09:56 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 13:08 -0700
                Re: Boxed MCU with RS-232 Port Jim Jackson <jj@franjam.org.uk> - 2023-03-27 20:46 +0000
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 15:07 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 15:07 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 14:50 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 15:07 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 15:24 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 15:36 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 15:37 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 15:42 -0700
                Re: Boxed MCU with RS-232 Port David Brown <david.brown@hesbynett.no> - 2023-03-27 11:03 +0200
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 07:11 -0700
                Re: Boxed MCU with RS-232 Port Dimiter_Popoff <dp@tgi-sci.com> - 2023-03-27 17:47 +0300
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 08:05 -0700
                Re: Boxed MCU with RS-232 Port Dimiter_Popoff <dp@tgi-sci.com> - 2023-03-27 19:09 +0300
                Re: Boxed MCU with RS-232 Port David Brown <david.brown@hesbynett.no> - 2023-03-27 17:38 +0200
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-26 19:22 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-26 19:11 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-26 13:37 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-26 19:28 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 13:38 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 15:05 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 15:08 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 15:25 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 15:38 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-26 13:23 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-26 19:25 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-26 20:31 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 07:05 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 09:18 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 10:09 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 12:16 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 13:03 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 13:17 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 15:05 -0700
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-27 15:40 -0700
                Re: Boxed MCU with RS-232 Port Clifford Heath <no.spam@please.net> - 2023-03-28 10:36 +1100
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 17:59 -0700
                Re: Boxed MCU with RS-232 Port Clifford Heath <no.spam@please.net> - 2023-03-28 12:58 +1100
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 20:41 -0700
                Re: Boxed MCU with RS-232 Port Clifford Heath <no.spam@please.net> - 2023-03-28 15:21 +1100
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-28 08:37 -0700
                Re: Boxed MCU with RS-232 Port Jim Jackson <jj@franjam.org.uk> - 2023-03-28 20:00 +0000
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-28 13:06 -0700
                Re: Boxed MCU with RS-232 Port Clifford Heath <no.spam@please.net> - 2023-03-29 08:03 +1100
                Re: Boxed MCU with RS-232 Port Don Y <blockedofcourse@foo.invalid> - 2023-03-28 00:11 -0700
                Re: Boxed MCU with RS-232 Port "b...@gmx.com" <bl1@gmx.com> - 2023-03-27 16:17 -0700
                Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 18:12 -0700
                Re: Boxed MCU with RS-232 Port Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2023-03-24 19:26 +0100
              Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 08:03 -0700
                Re: Boxed MCU with RS-232 Port Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2023-03-24 19:10 +0100
    Re: Boxed MCU with RS-232 Port Herbert Kleebauer <klee@unibwm.de> - 2023-03-24 17:16 +0100
      Re: Boxed MCU with RS-232 Port Herbert Kleebauer <klee@unibwm.de> - 2023-03-24 18:54 +0100
      Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-24 11:34 -0700
  Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-27 10:18 -0700
  Re: Boxed MCU with RS-232 Port Uwe Bonnes <bon@hertz.ikp.physik.tu-darmstadt.de> - 2023-03-28 20:53 +0000
    Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-28 16:12 -0700
      Re: Boxed MCU with RS-232 Port Niklas Holsti <niklas.holsti@tidorum.invalid> - 2023-03-29 09:06 +0300
        Re: Boxed MCU with RS-232 Port Rick C <gnuarm.deletethisbit@gmail.com> - 2023-03-29 00:44 -0700

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