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RS232 issues on cRIO chassis using NI9870s

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I have been struggling with an issue for several weeks now and so I am posting here to see if anyone else has experienced this or knows what I am doing wrong.

I have a setup running LabVIEW .exes designed to control and record output from a number of devices for testing purposes, the primary interface for these devices is RS232 and as we wanted to test up to 12 devices we bought a cRIO 9056 cassis and three NI9870 modules to provide the RS232 channels.  I am using these modules in real time scan mode in order to access them on the host PC.

I am using the vi linked in this post to send commands and receive the response.

My issue is that the program runs fine for a  while and then I will get periods where ether the VI or the chassis (unsure which) will freeze for a period of time and not respond, I have timeouts in place that should end the attempt but the timeouts do not work when this is happening and the vi will sit there for a few minutes before eventually giving up.  It will then resume normal operation for a bit.  It will repeat this cycle for a while then eventually stop responding all together with the VI attempting a connection for a bit then after a while its as though the RS232 ports are not there at all.

when in this state I get this error:


The remote machine does not exist or is not accepting any connections. If the NI-VISA server is installed and running on the remote machine, it might have an incompatible version or might be listening on a different port.

I see this error on the chassis


and this is what the chassis main page looks like


the only way I have found to recover it from this state is a physical power cycle, software reset does not work.

We have another identical chassis which I plugged in with the same results so I have ruled out a hardware issue.


Am I doing something wrong with handling my RS232 ports?  any help would be greatly appreciated.

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I found an article, which I think giving exact solution for this situation. Try to go step-by-step through that article.



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My issue turned out to be opening and closing the RS232 interfaces too often, apparently doing this to much will cause the cRIO to become unresponsive as although I was closing the port the Linux system on the cRIO still had it reserved.

I changed my RS232 vi to check the speed of the visa resource as I am using 115200 so if the speed was 9600 I opened the port, and if it was 115200 I skip to the read write operation.  Since making this change I have not had any issue.

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