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Re: Serial Bus Speed on PCs

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On 2022-11-30, Rick C <gnuarm.deletethisbit@gmail.com> wrote:
> I am using laptops to control test fixtures via a USB serial port.  I'm looking at combining many test fixtures in one chassis, controlled over one serial port.  The problem I'm concerned about is not the speed of the bus, which can range up to 10 Mbps.  It's the interface to the serial port.  
>
> The messages are all short, around 15 characters.  The master PC addresses a slave and the slave promptly replies.  It seems this message level hand shake creates a bottle neck in every interface I've looked at. 
>
> FTDI has a high-speed USB cable that is likely limited by the 8 kHz polling rate.  So the message and response pair would be limited to 4 kHz.  Spread over 256 end points, that's only 16 message pairs a second to each target.  That might be workable if there were no other delays. 

Use some multidrop standard at the physical layer such as RS485.
At the DLL adopt a token ring style arbitration system.  The first
device interprets the request from the host as both receiving the
token and a request for data - for consistency with the other units
you'd probably want to format that initial request as a dumy "Device
0" response.  Device N interprets the reply from N-1 as sending it
the token and its request to transmit.  From the host perspective
you send a single request and get back a byte stream with the
results from all devices.

-- 
Andrew Smallshaw
andrews@sdf.org

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Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-29 23:33 -0800
  Re: Serial Bus Speed on PCs Richard Damon <Richard@Damon-Family.org> - 2022-11-30 07:42 -0500
    Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-30 06:21 -0800
      Re: Serial Bus Speed on PCs Bernd Linsel <bl1-removethis@gmx.com> - 2022-11-30 16:11 +0100
        Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-30 07:58 -0800
          Re: Serial Bus Speed on PCs David Brown <david.brown@hesbynett.no> - 2022-11-30 18:14 +0100
            Re: Serial Bus Speed on PCs Dimiter_Popoff <dp@tgi-sci.com> - 2022-11-30 20:52 +0200
            Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-03 12:42 -0800
              Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-03 12:55 -0800
              Re: Serial Bus Speed on PCs David Brown <david.brown@hesbynett.no> - 2022-12-04 13:21 +0100
                Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-04 08:54 -0800
                Re: Serial Bus Speed on PCs David Brown <david.brown@hesbynett.no> - 2022-12-05 08:57 +0100
                Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-05 14:12 -0800
  Re: Serial Bus Speed on PCs antispam@math.uni.wroc.pl - 2022-12-01 01:08 +0000
    Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-01 02:48 -0800
      Re: Serial Bus Speed on PCs David Brown <david.brown@hesbynett.no> - 2022-12-02 13:30 +0100
        Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-02 09:01 -0800
      Re: Serial Bus Speed on PCs antispam@math.uni.wroc.pl - 2022-12-04 21:30 +0000
        Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-04 14:57 -0800
          Re: Serial Bus Speed on PCs antispam@math.uni.wroc.pl - 2022-12-05 03:33 +0000
            Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-04 22:39 -0800
              Re: Serial Bus Speed on PCs antispam@math.uni.wroc.pl - 2022-12-06 02:30 +0000
                Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-05 23:41 -0800
                Re: Serial Bus Speed on PCs David Brown <david.brown@hesbynett.no> - 2022-12-06 13:32 +0100
                Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-06 18:03 -0800
                Re: Serial Bus Speed on PCs David Brown <david.brown@hesbynett.no> - 2022-12-07 08:08 +0100
                Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-07 03:36 -0800
  Re: Serial Bus Speed on PCs Andrew Smallshaw <andrews@sdf.org> - 2022-12-05 09:58 +0000
    Re: Serial Bus Speed on PCs Rick C <gnuarm.deletethisbit@gmail.com> - 2022-12-05 14:03 -0800

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