Labview crio9064 serial problem

[MattBHGE]

I am stuck with a problem with the crio communicating through the serial port to an Alicat flow controller.

It was working before Christmas and haven't been back since.  Got here today and tried to run it and it would not run.  Verified wiring and then used a serial to usb connector to my pc to verify through simply modbus that it works and the wiring and the alicat are working fine.  So I tried to download the ni-visa incase it was bad but once I got it downloaded it goes to installer and shows no action.

The controller should be outputting the info but I just cannot get it to read.  When I go to shutdown the program using the stop button it says timeout.

I'm really at a loss why it worked and now it doesn't?  Any ideas on what it could be?  

[Kevin_Alicat]

Hi Matt,

Just to double check: the Alicat device communicates over the serial Modbus communication to a PC via a USB converter, but does not communicate to the cRIO serial port (verifying that the Alicat hardware is able to communicate well, but that there's an issue elsewhere). Is that right? 

If your device communicates over RS-232 (Alicat's default for serial communication), have you double checked that there is a valid ground connection between the Alicat and the cRIO serial port? Alicat RS-232 uses effectively inverted TTL logic levels of 0-5 VDC rather than the 232 specification of ±3-15 VDC. Most 232 adapters are fine with the 0-5 VDC signals, but it can cause issues for some if it's either a homebrew transceiver or if the ground is not present (since a shift in ground reference between the Alicat and the serial port can be enough to drop/raise the voltage above the 0/1 thresholds). If the ground is not connected from the Alicat connector to the cRIO serial connector, you could get intermittent communication problems, depending on the voltages of the two grounds. 

If the grounds are connected and it's still giving issues, it could potentially be a dead serial port or a driver issue like you had mentioned. With a dead/dying serial port, depending on how it is dying or how far gone it is you can sometimes get things to limp on for a while by dropping the baud rates down to a low value. I've had a COM port die on me in a way that the higher bauds were no longer usable but something like 2400 baud was still functional. 

Last thought I have is depending on the state it was in on close, I know serial resources can sometimes get locked up in LabVIEW and prevent proper access (but these often give errors of being unable to open/access the COM port). I'm assuming you've tried the old IT fix of turning it off and on again?

Hopefully this is of some use, but definitely feel free to let me know if you have any additional questions and I will be happy to assist.