Can Python serial support run at 45.45 baud?
google at mrabarnett.plus.com
Sat Feb 14 19:07:20 CET 2009
John Nagle wrote:
> Grant Edwards wrote:
>> On 2009-02-14, John Nagle <nagle at animats.com> wrote:
>>> Can Python's serial port support be made to run at 45.45 baud,
>>> the old "60 speed" Teletype machine speed?
>> If your hardware and OS supports it, Python can be made to
>> support it.
> OK, tried to open the port, using Python 2.6, latest PySerial
> and PyWin32:
> ser = serial.Serial(port, baudrate=baud,
> Traceback (most recent call last):
> File "serialtest.py", line 27, in <module>
> File "serialtest.py", line 24, in main
> ser = openportbaudot(0,45.45)
> File "serialtest.py", line 17, in openportbaudot
> File "D:\python26\lib\site-packages\serial\serialutil.py", line 171,
> in __init__
> File "D:\python26\lib\site-packages\serial\serialwin32.py", line 63,
> in open
> File "D:\python26\lib\site-packages\serial\serialwin32.py", line 171,
> in _reconfigurePort
> raise ValueError("Cannot configure port, some setting was wrong.
> Original message: %s" % e)
> ValueError: Cannot configure port, some setting was wrong. Original
> message: (87, 'SetCommState', 'The parameter is incorrect.')
> Something doesn't like "serial.FIVEBITS". That's a valid value,
> to "http://pyserial.wiki.sourceforge.net/pySerial". If changed to
> "serial.EIGHTBITS", the code will execute, but of course does the wrong
> thing. That looks like a bug.
> I tried various values for "baud". PySerial will accept "45", and
> even "45.45", although I doubt that it's really calculating the serial
> port divisor
> values from a floating point value. (Standard serial port hardware can do
> 45.45 baud, and most PCs with non-USB serial ports will do it quite well.)
> For my application, 45 baud should work, with two stop bits; the
> tolerances aren't that tight.
I don't think it's a Python bug. The MSDN website says this:
When a DCB structure is used to configure the 8250, the following
restrictions apply to the values specified for the ByteSize and StopBits
* The number of data bits must be 5 to 8 bits.
* The use of 5 data bits with 2 stop bits is an invalid
combination, as is 6, 7, or 8 data bits with 1.5 stop bits.
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