Modbus with motor drive

[jdruano]

Hi,

I was connecting Labview with an Altivar 31 AC motor drive using modbus.

It worked fine but I realized that according to drive datasheet a register 9096, for instance, appears to be read by Labview in the address 9097.

I do not know why all the registers appeared one position delayed according to datasheet.

Could anyone help me?

[RavensFan]

You may have sadi that backwards.

There is always a bit of confusion between what is listed as the register address in a device manual, and the number that is actually used in LabVIEW and sent to the device in serial or TCP/IP to read it.

So a register such as 40001 in the manual, drop the 4,  subtract 1.  and you issue the request as 0.

404097 in the manual, you'd send the request as 9096.

It is actually not a LabVIEW thing, just a difference between the formal register number and the address number that is actually sent in the background.  In the background it uses the lower number.  The NI modbus library uses the lower number.  If you were doing this using DSC and a modbus server in a project, you'd use the 4 and the higher number, basically the formal address that the manual would probably refer to.

[jdruano]

Sorry if I said it wrong, english is not my first language.

Thanks for your help but I am not quite sure about your answer. Basically you are telling me that the Labview address may not start or match exactly as the device manual says?

[RavensFan]

Yes.

If the manual says register 40205.  You will use the number 204 if you are using the NI modbus library.