pyserial: Unexpected Local Echo

Grant Edwards invalid at invalid.invalid
Mon Jan 11 21:02:37 CET 2010

On 2010-01-11, Steven Woody <narkewoody at> wrote:

> I am using pyserial.  But I always get the local echo after I
> write some characters onto serial port

I really doubt you're getting a local echo.  Is the data coming
out the serial port?  Do you get the echo if you disconnect the
serial cable?

> and I find no way to disable this behavior. When I say 'local
> echo', I mean the next read operation will get characters that
> was just write to the same port.

The device to which you're connected is echoing them.  There's
also a chance that your rxd line is floating and there's enough
crosstalk in the cable to "echo" the data, but I'll bet money
it's not being done locally (in the serial driver or port).

> I run my program on cygwin (pyserial was also built on the
> system from source code) and the serial port i am using is a
> USB adapter that simulates a port (COM4 on my XP) because my
> laptop don't have a real serial port.  But I checked my COM4
> settings, there is no any think like 'local echo'.

Grant Edwards                   grante             Yow! Will it improve my
                                  at               CASH FLOW?

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