WLF4 Utility MODBUS RTU Receive Message "ERROR"

[mcnearymw]

Using the WLF4 Utility to communicate with a Watlow controller I get a framing error at every Visa read.  I've checked the port settings but can't seem to locate the problem. The attached image is the block dia from the WLF4 Initalize.vi -> ...Read From Register.vi -> ... MODBUS RTU Receive Message.vi

  

[Nick-C]

mcnearymw,

This VISA error typically happens when the device is still trying to complete its configuration and is queried for information. Take a look at this knowledge base article. Hope this information is helpful.

-Nick-

[bluedog2112]

I am having a similar timeout error (-1073807339) . I have stuck 100msec delays before and after the read visa with no change. I am attempting to communicate with an F4 controller with a very simple vi (using NI WATLOW drivers). I am starting a profile, aborting a profile, current step, current temp. Real simple right? I started my project by validating hardware and I used Watview as a sanity check. The communication path is F4D (RS485) / RS485 to RS232 converter /RS232 to USB converter /PXI chassis.

During development the vi worked fine. After saving my project, I shutdown Labview, restarted labview, restarted my vi and then the MODBUS RTU RECIEVE message error (timeout). I did the usual check of comm port with MAX, revalidated hardware with Watview (verified the Watlow read the thermocouple), and still MODBUS RTU RECIEVE message error (timeout).

I have confirmed that there is a combination of opening my project, starting my vi, then starting the NI "CLOSE" vi, restarting my vi, which clears the timeout problem. If I were to close Labview and reopen my vi, problem reappears.

any ideas?

[mudson]

Hello bluedog2112,

Looking at the KB mentioned by Nick-C, there was a three-step procedure involved:

*Configure VISA port

*Wait
*Flush VISA buffer

With the current procedure

"...Open project, start vi, start NI-close, restart vi..."
Do you receive the time-out error on the initial run of your VI?  Or do you only get the time out on subsequent runs if the NI "Close" vi isn't called?

Best regards,

[mpencke]

I created a sub vi called patch (see attachment). I tried this patch outside and inside the case statement prior to the visa read. I have tried changing bauds.

I have always gotten the timeout error right off the bat (initial run of my vi). Whatever I did opening and closing the "close vi" doesn't seem to be repeatable. This probably should be a clue.

thanks

[dstrandb]

Hi mpencke,

What exactly is the patch subVI doing? Does it contain a wait function in it to allow the configuration to be set before the read happens? If your VI times out everytime it is run, are you able to communicate with the device at all? You mention that the Close.vi doesn't seem to be repeatable. What specifically is not repeatable with the Close.vi?

[bluedog2112]

my patch contains this (see attachment Doc). I can't communicate with the device at all with labview. I take the exact same set-up (without moving or disconnecting anything) and execute "Watview", and I can communicate with the Watlow. The intermittant nature of sometimes I can communicate sometimes not, initially appeared to be related to running the "close vi" while my suspect vi was open. That appears to be a red herring.

[dstrandb]

Hi Bluedog/mpencke,

I see. Thanks for posting what was contained in the patch. Are you able to communicate with the device in Measurement & Automation Explorer using VISA test panels? Are you communicating with the instrument over Modbus?