PySerial rereads its own data

Greg Ewing (using g2h5dqi002 at
Wed Jun 4 04:42:16 CEST 2003

Cliff Wells wrote:
>>>My question is this:  why do I get back the data I just wrote?  More to
>>>the point, how do I stop it?

I missed your original post, so this is just a guess, but
are you by any chance trying to use the same file object
to both read and write the serial port?

I made that mistake once in C, and I got exactly that
symptom. It seems that stdio gets its buffering in a
knot if you try to do that.

If that's the problem, the solution is to open the
serial device twice, once for reading and once for
writing, e.g.

   fin  = open("/dev/ttyS0", "r") # read from this one
   fout = open("/dev/ttyS0", "w") # write to this one

Greg Ewing, Computer Science Dept,
University of Canterbury,	
Christchurch, New Zealand

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