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From: Steven Woody on 11 Jan 2010 10:27
Hi,

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

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'.


Thanks in advance.

--
Life is the only flaw in an otherwise perfect nonexistence
-- Schopenhauer

narke
public key at http://subkeys.pgp.net:11371 (narkewoody(a)gmail.com)
From: Steve Holden on 11 Jan 2010 10:43
Steven Woody wrote:
> Hi,
>
> I am using pyserial. But I always get the local echo after I write
> some characters onto serial port 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.
>
> 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'.
>
>
> Thanks in advance.
>
It sounds to me like the device you are connecting to implements
echoing. Have you tried connecting a terminal emulator to it?

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
PyCon is coming! Atlanta, Feb 2010 http://us.pycon.org/
Holden Web LLC http://www.holdenweb.com/
UPCOMING EVENTS: http://holdenweb.eventbrite.com/

From: Nobody on 11 Jan 2010 13:59
On Mon, 11 Jan 2010 23:27:03 +0800, Steven Woody wrote:

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

That explains the "echo" part. What makes you think that it's local?


From: Grant Edwards on 11 Jan 2010 15:02
On 2010-01-11, Steven Woody <narkewoody(a)gmail.com> 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?
visi.com
From: John Nagle on 15 Jan 2010 15:04
Grant Edwards wrote:
> On 2010-01-11, Steven Woody <narkewoody(a)gmail.com> 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'.

You're using what? Some version of Python built on Cygwin
running on a Windows XP system? What if you just run a stock
Python built for Windows on Windows XP? Or run Linux? That
half-and-half environment may not work right. pyserial has
special cases in it for Windows and Linux, and it's not
clear what it will do on Cygwin.

That said, if you're getting echo from output back to input,
I'd look at the USB to serial device. I've used devices with
the Silicon Laboratories CP2102 part, and they work fine.
("http://www.aetherltd.com/connectingusb.html")

Do you have something plugged into the serial port? If
so, what?

John Nagle
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