Modbus Communications 32 bit

[drewtreb]

I am programming a LabView 8.5 application and I need to communicate to a Watlow temperature controller via Modbus TCP.

The controller uses 32 bit floating point.

I know how to read two consecutive 16 bit registers to get a 32 bit word.

My problem is that the addressing structure of the Watlow starts at register 400,000 and goes up from there.

The NI Modbus library (which I have used on previous applications with different Watlow controllers) appears to only support 16 bit addresses.

I can not enter register values greater than 65,535 for my reads and writes.

How can I read the "high-address" register values in the Watlow controller?

[RavensFan · Accepted solution]

The 4 in 40,000 is assumed. You don't actually enter it.   If you are looking for register 40,012 for instance, just enter the number 11 as the address.  (Because in LabVIEW, the addresses start at 0)

[drewtreb]

Thanks for the help.

[RavensFan]

Actually, if you needed to enter the 4, it would not just be a problem for LabVIEW, but all Modbus applications, because only 2 bytes are reserved in the message protocol for the address.

I'm glad it worked.  But please mark my reply #2 as the solution, then.

Message Edited by Ravens Fan on 04-21-2009 01:43 PM