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Re: Serial Port Emulation

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On 20/02/2019 04:40, gnuarm.deletethisbit@gmail.com wrote:
> On Tuesday, February 19, 2019 at 5:35:22 PM UTC-5, Theo wrote:
>> David Brown <david.brown@hesbynett.no> wrote:
>>> There are far too many "standard" USB connectors - especially when
>>> considering long-term systems.  Serial (be it TTL UART, RS-232, RS-485 or
>>> RS-422) has a big advantage for connectors that it really doesn't matter. 
>>> You need three wires (5 for RS-422), and there are no issues with speed,
>>> impedance, or anything like that.  An RS-232 9-pin DSUB may be convenient,
>>> but any connector will work fine and can be jerry-rigged as needed.  And
>>> the various UART standards are simple, can be bit-banged, and just need a
>>> simple driver.  That is a big plus for long-lasting systems.
>>
>> I don't really see the problem with USB.  It's 4 wires: VCC, D-, D+, GND
>> Route that to a pin header, you can bodge something on to that just like
>> serial.  If you're running at USB 1.1 speeds then wire length isn't really
>> an issue (any more than it is with TTL UART anyway).  Bonus points if you use
>> the same pinout at PC motherboard headers so their standard cabling will
>> work.
> 
> Low speed USB was designed for very simple implementations and is 1.5 Mbps raw data rate which is about as fast as UARTs are typically run.  However there are timing issues that limit cable length, at least for the higher speeds.  I think low speed is length limited to <10 feet to allow inexpensive drivers and cable. 
> 

Yes, the low speed USB is not too bad - at those speeds you don't have
to worry about connectors, impedances, length matching, etc.  And it is
possible to bit-bang it if you have to.  But it is still more effort
than handling a UART at that speed, especially on the software side.

5m USB cables are not uncommon, but beyond that you tend to have active
cables (with a USB hub in the middle).


> 
>> If you choose to put a port on the back of a machine then people will need a
>> cable for that.  They might not have the right one, and their local
>> supermarket might not have the right one, but they can order one.  It's no
>> worse than TTL UART.
> 
> Most USB stuff these days is micro-USB.  Type-C is gaining ground with phones and tablets, mostly because of the charging capabilities.  
> 
> Serial ports, either TTL or RS-232, have a plethora of connectors used.  I've seen, DB-25, DB-9, RJ-11, RJ-45 in multiple pinouts, 0.1" spaced 0.025" square posts in sum(n!) configurations where n ranges from 3 to 9.  
> 
> 
>> I agree that UART is so simple that any microcontroller ever should be able
>> to bit bang it, which helps.
> 
> That's why every design I do determines the interface by the requirements, not by a predefined choice of one size fits all. 

Yes, I agree.

(But one of the requirements I put on most new designs is a 3-pin or
6-pin header for an FTDI TTL UART to USB cable for debugging output.)

> 
> I'm currently looking at rolling a design that will use an FTDI chip for it's JTAG capabilities as well as providing a UART.  But the package is larger than the device I want to control. 
> 

If you make sure your pinning on the FTDI chip matches those supported
by OpenOCD (which can support a great variety of choices here), then
your board has a built-in debugger.  I did done something similar with a
Coldfire board many years ago - it was a great convenience in test and
programming.

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Serial Port Emulation gnuarm.deletethisbit@gmail.com - 2019-02-17 02:08 -0800
  Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-02-17 13:42 +0100
    Re: Serial Port Emulation Chris <xxx.syseng.yyy@gfsys.co.uk> - 2019-02-17 15:49 +0000
  Re: Serial Port Emulation Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2019-02-17 18:54 +0200
    Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-02-17 21:16 +0100
      Re: Serial Port Emulation Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2019-02-18 10:38 +0200
        Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-02-18 10:49 +0100
          Re: Serial Port Emulation Richard Damon <Richard@Damon-Family.org> - 2019-02-18 07:25 -0500
            Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-02-18 14:31 +0100
              Re: Serial Port Emulation Andrew Smallshaw <andrews@sdf.org> - 2019-02-19 16:10 +0000
                Re: Serial Port Emulation gnuarm.deletethisbit@gmail.com - 2019-02-19 09:12 -0800
                Re: Serial Port Emulation upsidedown@downunder.com - 2019-02-19 19:58 +0200
                Re: Serial Port Emulation Grant Edwards <invalid@invalid.invalid> - 2019-02-19 18:22 +0000
                Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-02-19 22:50 +0100
                Re: Serial Port Emulation Grant Edwards <invalid@invalid.invalid> - 2019-02-19 22:23 +0000
                Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-02-20 08:53 +0100
                Re: Serial Port Emulation upsidedown@downunder.com - 2019-02-20 10:17 +0200
                Re: Serial Port Emulation Theo <theom+news@chiark.greenend.org.uk> - 2019-02-19 22:35 +0000
                Re: Serial Port Emulation upsidedown@downunder.com - 2019-02-20 01:36 +0200
                Re: Serial Port Emulation gnuarm.deletethisbit@gmail.com - 2019-02-19 19:40 -0800
                Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-02-20 09:00 +0100
                Re: Serial Port Emulation upsidedown@downunder.com - 2019-02-19 19:16 +0200
                Re: Serial Port Emulation Theo <theom+news@chiark.greenend.org.uk> - 2019-02-19 22:28 +0000
                Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-02-20 10:32 +0100
                Re: Serial Port Emulation Robert Wessel <robertwessel2@yahoo.com> - 2019-02-19 18:44 -0600
                Re: Serial Port Emulation Les Cargill <lcargill99@comcast.com> - 2019-02-23 14:48 -0600
                Re: Serial Port Emulation Robert Wessel <robertwessel2@yahoo.com> - 2019-02-23 16:34 -0600
                Re: Serial Port Emulation Les Cargill <lcargill99@comcast.com> - 2019-02-27 22:15 -0600
                Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-02-28 08:41 +0100
                Re: Serial Port Emulation gnuarm.deletethisbit@gmail.com - 2019-02-28 15:07 -0800
                Re: Serial Port Emulation David Brown <david.brown@hesbynett.no> - 2019-03-01 10:04 +0100
                Re: Serial Port Emulation gnuarm.deletethisbit@gmail.com - 2019-03-01 13:09 -0800
                Re: Serial Port Emulation Les Cargill <lcargill99@comcast.com> - 2019-03-04 17:58 -0600
                Re: Serial Port Emulation Paul Rubin <no.email@nospam.invalid> - 2019-03-01 02:25 -0800
                Re: Serial Port Emulation gnuarm.deletethisbit@gmail.com - 2019-03-01 13:16 -0800
                Re: Serial Port Emulation Paul Rubin <no.email@nospam.invalid> - 2019-03-01 16:45 -0800
                Re: Serial Port Emulation Les Cargill <lcargill99@comcast.com> - 2019-03-04 17:44 -0600
                Re: Serial Port Emulation Richard Damon <Richard@Damon-Family.org> - 2019-02-23 19:37 -0500
                Re: Serial Port Emulation Les Cargill <lcargill99@comcast.com> - 2019-02-27 22:17 -0600
          Re: Serial Port Emulation gnuarm.deletethisbit@gmail.com - 2019-02-18 06:28 -0800
          Re: Serial Port Emulation Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2019-02-18 22:33 +0100
  Re: Serial Port Emulation "A.P.Richelieu" <aprichelieu@gmail.com> - 2019-02-17 21:06 +0100
  Re: Serial Port Emulation raimond.dragomir@gmail.com - 2019-02-17 21:56 -0800
    Re: Serial Port Emulation gnuarm.deletethisbit@gmail.com - 2019-02-17 22:37 -0800
  Re: Serial Port Emulation "Mat Nieuwenhoven" <mnieuw@zap.a2000.nl> - 2019-02-18 12:34 +0100

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