Determining communication path between processors

Hey everyone,

I'm an electrical engineer in training (currently on co-op), and I have been assigned my first large project that deals heavily with discrete logic over Ethernet and data highway. I am attempting to update the current logic to allow for additional steps within various sequences, however, I am not entirely certain as to how data is currently being mapped between the processors.

The machine I am working on has two separate processors that interact with one another. The main processor for this line is an Allen Bradley L62, and the second is a SLC.

The L62 (let's call it Rack A) has three Ethernet cards within its rack. The SLC has a single Data Highway connection to a different Logix5000 rack (let's call the second Logix5000 chassis Rack B). Rack B has two Ethernet cards associated with it.

Since Rack A is sending data to the SLC, I am assuming that the data is being sent to Rack B via the Ethernet connection, and then to the SLC via Data Highway.

Looking at the logic in Rack A, I can see that the data is being sent via the following tags:
<CP3:O.Slot[4].Data.13>
<CP3:O.Slot[6].Data.4>
<CP3:O.Slot[6].Data.2>

From looking at these tags, how am I supposed to know that the data is being transferred to the SLC and how am I supposed to know which path that data is taking?

1 option: ControlLogix sending data to the SLC - Look for a message (MSG) instruction.
2 option: SLC reading data from the ControlLogix. This would require a MSG Map - in the RSLogix 5000 with the program open, go to the Logic tab, then there is an entry "MAP PLC/SLC Messages". If there is a table there, then the SLC could have MSG's to read from the ControlLogix.

kubiej21 said:

[1]Since Rack A is sending data to the SLC, [2]I am assuming that the data is being sent to Rack B via the Ethernet connection, and then to the SLC via Data Highway.

From looking at these tags, [3]how am I supposed to know that the data is being transferred to the SLC and [4]how am I supposed to know which path that data is taking?

Click to expand...

[1] If the ConrolLogix is writing data to the SLC then there will be a MSG instruction in the L62.

[2] No assumptions needed, that's the only path the message can take, although it could be routed through any on of the 3 EtherNet modules in "Rack A", and through either of the 2 EtherNet modules in "Rack B".

[3] Very simply, the MSG tag's "Done" (.DN) bit indicates a successful transfer.

[4] Look at the message configuration (click the [...] box inside the instruction), and then choose the "Connection" tab. The path is shown on that tab.

Message paths are straightforward once you understand the "rules".

A "path" consists of repetitive pairs of "Port, Destination" specifications (i.e. "leaving from, going to").


An example, based on your configuration (although I don't know your slot numbers for the modules, or addresses for the network nodes, but you should be able to substitute).

L62 in Rack A - message has to leave by the rear (backplane) port. This is always port 1.
ENET/ENBT/EN2T comms module in slot 6.

Message path (so far) is 1,6,...

Message has to be routed out to the Ethernet port on the ENET/ENBT/EN2T. This is port 2.
Message destination is the Ethernet address of a comms module in Rack B, e.g. 192.168.1.55

Message path (so far) is 1,6,2,192.168.1.55...

Message has to be routed onto the backplane in Rack B. Port 1.
Message has to arrive at the DH/DHRIO module in slot 4.

Message path (so far) is 1,6,2,192.168.1.55,1,4...

Message is then routed out the front of the DH/DHRIO module, from either the "A" port (2), or the "B" port (3). Lets say we are using the "A" port 2.
The Destination for the message is the DH address of the SLC let's say 03.

Message path (complete) is 1,6,2,192.168.1.55,1,4,2,3

You should always end up with an EVEN number of parameters separated by commas for a message path specification. I have 8 above.

Now if you look at the path in your project, you may find exactly what I have described, or you may find that one or more pairs of the "port, destination" specifications has been replaced by the name of the module if it exists in the ControlLogix I/O configuration tree. Putting them in the I/O configuration is optional if all they are providing is a communication path, but lots of people put them in anyway.

So, If my Ethernet comms module in slot 6 has been entered into the I/O tree, and named "Eth_6", then that would replace the 1,6 parameters in the path.

Message path is now Eth_6,2,192.168.1.55,1,4,2,3

If the remote Ethernet module has been entered into the configuration, named "RackB", then that name replaces the part of the path that gets you to it.

Message path is now RackB,1,4,2,3

Once you've got a handle on this simple scheme, message paths are fairly simple.

HTH