Logix5000 Ethernet Messanging

Hi all,

I'm trying to setup Ethernet messaging.
The following describes it very well:
http://www.plctalk.net/qanda/showthread.php?t=51059

I have the following setup though. 4 PLC controllers and one Ethernet card in the same rack (S0 - PLC0, S1 - PLC1, S2 - PLC2, S3 - PLC3, S4 - ENT). If I just point the message path to the PLC, they will communicate over the backplane.

Is it possible for them to communicate over Ethernet? (I know it will probably slower. Experiment)
eg. PLC0 read from PLC1 (xxx.xxx.xxx.xxx - IP address)
1,4,2,xxx.xxx.xxx.xxx,1,1

Once you have the I/O tree definitions in each PLC program for the other PLCs, research Produce-Consumed tags. Much easier then using the message instructions.

jstolaruk said:

Once you have the I/O tree definitions in each PLC program for the other PLCs, research Produce-Consumed tags. Much easier then using the message instructions.

Click to expand...

As far as I know people're getting rid of Produce-Consume tags these days, reverting back to messanging. Even Rockwell pushes people away from them.

alexbeatle said:

As far as I know people're getting rid of Produce-Consume tags these days, reverting back to messanging. Even Rockwell pushes people away from them.

Click to expand...

That is very surprising and I had not heard that. Can you provide a reference?

alexbeatle said:

As far as I know people're getting rid of Produce-Consume tags these days, reverting back to messanging.

Click to expand...

That is one of the most absurd statements I have ever heard!...

alexbeatle said:

Even Rockwell pushes people away from them.

Click to expand...

And that's the most egregious 'alternative facts' type piece of information ever posted on the web...Et tu Canada?!...

alexbeatle said:

As far as I know people're getting rid of Produce-Consume tags these days, reverting back to messanging. Even Rockwell pushes people away from them.

Click to expand...

????????????????????????????????????????????

It's entirely possible that some Rockwell support persons are recommending unscheduled messaging for a specific system with specific needs.

But I'm confident that Rockwell isn't attempting to down-sell one of the core features of the ControlLogix family controllers.

Back to your original question: it sounds like you want to communicate between controllers that are in the same backplane, but via an Ethernet module.

This will work only if you add another Ethernet module.

A 1756-ENBT module (or similar module) cannot send an Ethernet message to itself.

There is no "loopback adapter" feature (at least, none that is accessible to the user) in the 1756 Ethernet modules.

As you have discerned, the fastest way to communicate between CPUs in the same chassis is to use Produced/Consumed Tags. In most cases, this is also the simplest method.

The question of messaging vs. produce consume is one issue. They each have their advantages and disadvantages.

The question of routing either one across the backplane vs. thru an Ethernet module is a separate issue. You have exactly the same problem with messages or produce consume. You need a route. As Ken pointed out, you can't route through the Ethernet with only one card. You need to actually go out the Ethernet port and into a different Ethernet card.

Installing two Ethernet cards and routing between them is useful if you are testing a system where the processors will eventually be placed in separate chassis. I've done this pretty often. Otherwise it is simply a waste of time and equipment.

Technically P/C wasn’t intended to be used the way a lot of people are using it. It wasn’t designed to replace message instructions but rather create “real time” I/O. Messaging takes more time to accomplish and there is a need out there to have I/O connections that are very close to real time. With P/C the Ethernet connection is opened and left open so exchanging data doesn’t involve that part of the process (open the connection, pass the data, close the connection). It gets more complicated but that’s the short version. However once programmers found out that they could exchange data without having to write ladder logic (I.E. message instructions), that all they had to do is get the data from the tag within the PAC, P/C took off and has turned into a “gotta have it (even if I don’t need it)”. Having said that when you have a solid Ethernet connection between the devices exchanging the data there really isn’t a lot of reasons to not use it. Having said THAT, if you don’t have a reliable network and/or it’s crowded then you should message to exchange the data (not a scenario you see too often anymore). If you are going to use wireless, then you really need to message unless it is absolutely not possible and if that’s the case you should either rethink how the application is being put together or be very careful when designing it.
Just my 2 cents based off of my experience in the wireless world