polling variables using Modbus IP and labview 8.2.0 shared variables

[richjoh]

I'm using shared variable in order to read/write register on a Watlow PM controller over Modbus IP standard. Once I make a change to FP control, the shared variable polling starts and I no longer get update of any controls or indicators on the FP.

Just wondering if this is an LV 8.2.0 issue and if any of this is addressed in LV 8.5?

Thx ahead of time

richjoh

[Kevin_H]

Hey richjoh,

Thank you for contacting National Instruments.  I need to get a little more information about your modbus setup.  Are you using the DSC module within LabVIEW, or are you using the Modbus VI's?

Also, are you connecting to any sort of Modbus server?

I look forward to hearing back from you.

Regards,

Kevin H

[richjoh]

Kevin thanks for the response, I'm using DSC module within Labview. I'm using my PC and a Watlow PM controller thats it. (I guess the PC is the server). I don't have any code yet, just a library of Modbus shared variables (SV). I slide a few SV controls on the FP to observe and run a loop with a stop button that it.

Richjoh

[richjoh]

Kevin, there is a problem with the UpdateNow shared variable. It always shows X in the Variable Manager window. This is just a write only control and I have no idea why an X is shown while the others, i.e. "Updating, OffHook, Commfail and UpdateRate" appear OK.

Richjoh

[richjoh]

pic is attached below

[richjoh]

Kevin correction on my part, the Watlow PM is the controller.

[Jennifer_R]

Hi richjoh,

If I understand correctly, there are two issues to address: the status of the UpdateNow shared variable and the fact that your controls and indicators are not updating. 

When you right-click on UpdateNow in your project and select Properties, what is the data type listed there?  Is it bound to one of the other shared variables that has a value in Variable Manager?

After changing a control on the front panel, do you continue to see the values changing in Variable Manager even though the controls and indicators do not update on the front panel?  Do you see the same behavior regardless of which control you change? 

Thanks for the additional information. 

[richjoh]

Hi Jennifer_R. The data type for Updatenow is Boolean. All my Shared Variable are bound to one and only one Variable.

I tried to perform your observation regarding changing controls. I get an update after changing the control, but I was only able to see this after increasing the UpdateRate SV to something faster than 1. In the attached pic UpdateRate is set to 0.3. I get sporatic updates. Its as if I  have a syncronization problem over the Modbus tcp/ip. At this UpdateRate I get values read from registers but there are frequent Commfails. The PC and Watlow PM controller are connected through a 10Mbps Hub, both devices have a fixed address. Any ideas why I'm getting Commfails???

regards,

Richjoh

[richjoh]

whoops here's the attached pic

[richjoh]

Also, any SV dragged to my block diagram result in an error message whenever I run the VI. Error -1950679038 occurred at ni_tagger_lv_Read, see the attached.