Can Python serial support run at 45.45 baud?

John Nagle nagle at
Sat Feb 14 16:16:14 EST 2009

MRAB wrote:
> John Nagle wrote:
> [snip]
>> So the correct combination, 5 bits with 1.5 stop bits, isn't supported in
>> Python.  1 stop bit will not physically work on Baudot teletypes; the
>> main camshaft doesn't come around fast enough.  (Yes, there's an actual
>> mechanical reason for 1.5 stop bits.)  Requesting 2 stop bits at the
>> Python level gets a reject at the Win32 level.  (Not sure why Win32
>> doesn't allow that; extra stop bits just add delay, but don't hurt
>> anything.  But it's not supported.)

    I patched PySerial to support "STOPBITS_ONE5", for 1.5 stop bits,
and the big Teletype Model 15 is now banging out text from Python.

    I actually put in "45.45" as the baud rate; it gets rounded down
to 45 for Windows, which works.  That won't work on Linux, though;
there's a canned list of speeds for POSIX serial ports.  (It's the
same list PDP-11 serial ports had in the 1970s, plus some later
extensions at the high end.)

    1.5 or 2 stop bits is acceptable for the old heavy iron, but 1.5
is preferred, because there's less vibration and wear.  With 2 stop bits,
the Teletype Model 15 clutch drops out on every character and the drive
train momentarily comes to a halt.   With 1.5, everything rotates steadily.

					John Nagle

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