COM PORT ECHO

[alukindo]

Hi:

Is there a way to hold back a Serial COM Port from echoing back characters written to it? Can this be done from within LabVIEW?

I have this LabVIEW application which must poll a COM Port to get back data. However, the polling characters get echoed back giving the impression that the other system is talking back --while in-fact this is not the case.

Thanks for any help

Anthony

[orko]

Is there a way to hold back a Serial COM Port from echoing back characters written to it? Can this be done from within LabVIEW?

I have this LabVIEW application which must poll a COM Port to get back data. However, the polling characters get echoed back giving the impression that the other system is talking back --while in-fact this is not the case.

Anthony,

In my experiences the echoing either comes from the application sending the command (local echo) or from the *device* that is connected to the serial port. LabView (the programmer) has control over whether or not the commands are echoed back to the user on the display, but unless there's some sort of command you can send to your device that it understands, LabView has no control over turning a device's echo off. Since you were talking of a false response from the device, I'm assuming that your echo is coming from there.

What kind of device are you talking to through the serial port? Perhaps there's a way to turn its echo off?

Joe (orko)

[i2dx]

[...] Perhaps there's a way to turn its echo off?

yea, just take a big hammer and bash it on the device, i am sure this will turn the echo off immediatey ;-)

sorry, could not resist ;-)

and just to talk something seriuos:

i agree, it's very likely that the echo comes from the device. i have done a lot of coding for RS232 devices and i never stumbled uppon a "echo-function" in labview ...

[orko]

yea, just take a big hammer and bash it on the device, i am sure this will turn the echo off immediatey ;-)

...that didn't work on the last co-worker I had...

Anyway, make sure that the serial cable is unplugged before attempting this "percussive maintenance" fix.

Joe (orko)

[alukindo]

...that didn't work on the last co-worker I had...

Anyway, make sure that the serial cable is unplugged before attempting this "percussive maintenance" fix.

Joe (orko)

Thanks for input on this anomaly.

Actually the echo happens whithout any cable being present on the Comm Port. This is why users think that the cable connection is fine and everything while in-fact they are not even connected. I can find a way to filter the polling characters, but if I can turn echo off then I would go for that

Thanks again

Athony

[orko]

Actually the echo happens whithout any cable being present on the Comm Port. This is why users think that the cable connection is fine and everything while in-fact they are not even connected. I can find a way to filter the polling characters, but if I can turn echo off then I would go for that

I must not understand your setup correctly. Are you saying that you have LabView running on a PC, writing to the COM port, with no device connected? And you're getting echoes? Where's that Holloween "spooky" emoticon....

Anyway, if you are indeed in the above setup, then I would think it was your program, not your COM port that is creating this anomaly. Would you mind posting or emailing it to me?

Joe (orko)

[jpdrolet]

Thanks for input on this anomaly.

Actually the echo happens whithout any cable being present on the Comm Port. This is why users think that the cable connection is fine and everything while in-fact they are not even connected. I can find a way to filter the polling characters, but if I can turn echo off then I would go for that

Thanks again

Athony

I have seen (heard?) echoes on long unconnected RS232 cables (but connected at computer end). It was probably noise pickup between RX and TX. This should not happen when the cable is properly connected to a device. Or maybe there is a short somewhere between RX and TX. Are you running Windows XP? It has some issues with com ports

[Khalid]

Here's my typical solution to such problems: download Portmon (or any other such tool) and monitor the actual bytes going in and out of the Serial port. This should tell you who is the culprit!

http://www.sysinternals.com/utilities/portmon.html

Hope this helps.

-Khalid

PS: In Portmon, I find it easier to work if I set the mode to HEX, and filter unnecessary commands and just get the READs and WRITEs.