Can I write to Modbus I/O Server addresses without creating bound variables?

[JKSH]

Hi all,

I'm wondering if it's possible to use the Modbus I/O Server without explicitly creating bound variables?

• If I write a value to the bound variable at "ni.var.psp://My Computer/Slave/300001", the master can see the value.
• The variable properties paeg says that the variable is bound to "My Computer\Slave.lvlib\ModbusSlave1\300001"
• I deleted the bound variable and tried a few different ways to write directly to the I/O Server, but all of them gave me Error 0x8BBB0005. I tried the following:
• ni.var.psp://My Computer/Slave/300001
• ni.var.psp://My Computer/Slave/ModbusSlave1/300001
• ni.var.psp://My Computer/Slave.lvlib/ModbusSlave1/300001
• ni.var.psp://My Computer/Slave.lvlib/ModbusSlave1/300001

I also tried replacing "My Computer" with "localhost" above. No luck.

Is there anything I've missed? I'm asking because CPU usage is very high, and I thought I might be able to reduce that a bit by removing the 300 bound variables in the system.

[Dave_Brandt]

 You can use the modbus library to be a modbus master or slave. This does not use bound variable. You can add a comunication loop to your code. This gives you more control of the update rate and timeouts. You can down load the library http://www.ni.com/example/29756/en/

[JKSH]

Hi Dave,

Thanks for the recommendation. However, I'm hoping for an I/O Server based solution. At the moment, I don't actually know if I'll even benefit from getting rid of bound variables yet, so I don't want to rewrite my code yet.

If the bound variables are indeed the culprit for my high CPU usage, and if bound variables are the only way to use I/O Server, then I'll look at the low-level Modbus VIs.

[JKSH]

I just noticed a typo in my original post. The paths I tried are:

• ni.var.psp://My Computer/Slave/300001
• ni.var.psp://My Computer/Slave/ModbusSlave1/300001
• ni.var.psp://My Computer/Slave.lvlib/300001
• ni.var.psp://My Computer/Slave.lvlib/ModbusSlave1/300001

[MichaelBalzer · Accepted solution]

You can use DataSocket with a path like psp:\\localhost\Slave\ModbusSlave1.400001 for read and write access.

Check out the example VI "Monitor OPC Items with DataSocket.vi" in the LabVIEW examples.

[JKSH]

Thanks Michael! That worked perfectly.