[Logix5000] Manually setting address for MSG instruction

[defcon.klaxon]

I recently had to change the way my MSG instructions were connecting via ethernet radios; I originally had the remote PLCs in the I/O of the "master" PLC, but it was crashing the connection because of too much data. The solution was to manually tell the MSG instruction where to connect not by "browsing" to the I/O list, but rather to type out the IP address of the remote PLC.

The string in the path line at the "master" PLC is:

LCP_W_Ethernet, 2, 172.16.254.20

where:

LCP_W_Ethernet - name of the master PLC's ethernet module
2 - something to the effect of "go out to the ethernet"
172.16.254.21 - IP address of the remote PLC

Can someone clarify what that '2' means, and what (if any) other options there might be? I read that simply "it should always be '2'" but want to make sure things are set up correctly. I did a decent amount of searching for Rockwell Technical Documents that might describe this path, but couldn't seem to find anything that described manually creating the path (as opposed to adding the remote PLCs to the master's I/O).

Oh, and this is a master ControlLogix to a remote CompactLogix.

Thanks!

 

[Ken Roach]

CIP Path segments generally consist of a pair of values: a Port and an Address.

The name of the ControlLogix Ethernet module is shorthand for the first segment in the CIP Path. Under the hood, that CIP Path segment is "1, Slot".

In fact, if you typed this in as "1, x, 2, 172.16.254.20", where x is the ControlLogix slot number of the 1756-EN2T module, Studio 5000 would substitute the module name when you hit Enter.

1 is the port number for the ControlLogix backplane.
2 is the port number for the module's network port.
3 is the port number for the module's second network port, if it has one. The only module I know of that has ports 1, 2, and 3 is the 1756-DHRIO.

So in short, the "2" does mean "go out to the Ethernet".

CompactLogix makes some of this more complicated, especially because ther is a difference between the way the older popular 1769-L3xE and the modern 5370 controllers work.

In your case, just treat the CompactLogix IP address as the endpoint of the message and don't put any additional "backplane, CPU" CIP segments into the CIP Path.

 

[defcon.klaxon]

Thanks Ken! Very helpful and complete info.