RS-232 communication problem when ports are opened

[Mikeyws]

Hello,

         I'm attempting to make a program to send data between two computers using RS-232 protocol. Computer A is connected through its serial port and computer B is connected through a USB to serial port. I have the Rx and Tx signals of computer A hooked up to oscilloscope to monitor them. When computer A uses the command OpenComConfig or OpenCom the Rx signal looks like this: http://grauonline.de/wordpress/wp-content/uploads/noise_signal2.jpg. Computer A is able to successfully send data to computer B, but when computer B does the same, the data either doesn't come or it is completely messed up. I have the same issue using the LabWindows CVI example serial software and with Tera Term. However, when computer A is also using a USB to serial instead of its serial port this problem goes away and both computers are able to successfully communicate. Any ideas?

My code is attached. 

[mfaltin]

Hi Mikeyws,

What USB converter are you using? 

My suspicion is that the USB dongle that you are using is taking the RS232 data and converting it upon reception, however it does not convert it back to RS232 when sending. Thus when you use two USB dongles it works fine because both USB dongles are expecting the same thing.

-Mitchell | NI

[Mikeyws]

Hi mfaltin,

    I'm using this as my USB converter.

[mfaltin]

That is not a National Instruments piece of hardware. This sounds like a problem with your third party hardware, not with LabWindows/CVI.

Did you install the correct drivers?

Please use these forums for NI hardware and software. If you have problems with third party hardware, contact the manufacturer.

[Mikeyws]

I bought the NI USB converter and I still have the same problem. What do you think?