Modbus error

[Ryan Reliford]

I'm using the Modbus I/O server in LabVIEW 2010 to communicate with a Kohler generator.  A vendor was able to supply with the the Modbus address mapping so that I'd know what addresses correspond to what IO points.  One of the addresses is 40126 which I create in the Modbus I/O server as 400126 since it requires six digit addressing.  Well, that worked but only temporarily.  Not too long after I begin trying to make sense of the values read, the shared variable begins showing error -1967353908.  The description for this error is "The specified data item address is not an allowable address for the Modbus slave device. Refer to the documentation of the Modbus slave device for information about supported addresses."

What I don't understand is why it works one minute and stops working the next.  Also, I know that the Modbus server itself is not erroring b/c in my VI there are other boolean bit addresses that continue to report good data.  Can anyone assist in helping me figure this one out?  Thanks.

Ryan R.

[Austin_S]

Hi Ryan,

According to the LabVIEW 2010 and 2010 SP1 DSC Module Known Issues Developer Zone page, a Modbus Master IO Server will return error -1967353908 with certain modbus slave devices indicating that the master is reading from addresses that do not exist on the slave. This problem is actually caused because the IO Server is building a query for a range of values behind the scenes, some of which do not exist on the slave. The slave device then returns an exception that causes an error in the server.

The listed workaround for this issue is to reduce the number of Holding Registers in the Advanced Settings of the IO Server to 1. 

Give this a try and see if you still experience the same error being thrown.

[Ryan Reliford]

Thanks...I will try that.