ControlLogix EtherNet/IP Module Tags

[sabre123]

Hi All,

First, although I've been involved in the automation industry for a quite a while, it's been as a software developer and content developer for training programs, not as a PLC programmer. So I apologize in advance for any shortcomings in the following questions.

Platform: ControlLogix
Software: Studio 5000 or RSLogix 5000
No hardware so I can't go online

I'm trying to understand module-defined tags for an EN2T or ENBT Ethernet/IP module. The first thing I noticed was, when I added an EN2T to the I/O Configuration folder, no tags were added to the Controller Tags as they would be for an I/O module or another communications module such as a DeviceNet module. It was not until I added another EN2T module to the network of the first EN2T that Controller Tags had been added. In simple terms, why is that?

The tags created also seem to be just structures as opposed to being module-specific tags like those of an analog I/O module, for instance.

Can someone give me a real-world example of a binary value for the SlotStatusBits and any relationship of that value to the corresponding [module_name]:I.SlotStatusBits.0 - .31?

Also, I'd like an example of the [module_name]:I.Slot[0-31].Fault and [module_name]:I.Slot[0-31].Data.

Lastly, for [module_name]:O.Slot[0-31].Data elements, I'd like a real-world example of a binary value and/or explanation of how these tags are used in the system. Just a high level look.

Thank you in advance. I really appreciate your time.

Mark

 

[Ken Roach]

When you add a 1756-ENxT module to the controller backplane in the I/O tree, that first module is a "bridge". ControlNet and EtherNet/IP bridges don't have I/O connections of their own, so there are no I/O module tags created.

When you then add a 1756-ENxT module to the EtherNet/IP network, you select either "no connection" or "Rack Optimized" connection.

You would use No Connection if the remote chassis was going to be used only for Produced/Consumed Tags to another controller, or if it had only modules that used a Module connection themselves, like analog or diagnostic modules.

Your example questions pertain to Rack Optimized connections, where all the Discrete modules in the chassis have their data gathered together and transmitted in one chunk with one RPI rate. This makes a ControlLogix chassis work like a classic 1771 or 1746 rack, where all the data is transmitted at once and is designated by its Slot number and Bit number.

 

[Ken Roach]

[module_name]:I.SlotStatusBits.0 - .31

The Slot Status bits indicate that there is a discrete module present in that slot. There are 32 bits just because it's simplest to be a DINT datatype, even though the biggest ControlLogix chassis is 17 slots.

[module_name]:I.Slot[0-31].Fault

The Fault bits indicate that there is a module present and that it has faulted. This could be a module that established a connection and then underwent an internal failure, or one that was removed from the chassis. If there is no module present at powerup, you won't get a Fault, but rather simply no true bit in the Slot Status tag.

[module_name]:I.Slot[0-31].Data

These are the actual data objects for the discrete modules that are part of the Rack Optimized connection.

Here's where my understanding gets a little unclear. These automatically-created tags aren't what you address in the program, but rather the tags created for each Module that you create underneath the Rack object. Those Module connections are configured as "Rack Optimized" for most discrete modules that don't have Diagnostic features.

Clear as mud yet ?

 

[sabre123]

Hi Ken,

You've really done a nice job with your explanations and this is a great foundation for me to work from.

If I modify the properties of the remote EN2T and set its rack connection to none, the controller tags are now gone. I'm assuming that is because now the remote EN2T becomes another 'bridge' module for communications. Is this correct?

Thanks again,

Mark

 

[Ken Roach]

Yes, the remote chassis 1756-ENxT module can perform a handful of different functions, including:

1. Endpoint for cyclic Rack Optimized I/O Connection.
2. Bridge for cyclic Produced/Consumed Tag connections to a ControlLogix in that chassis.
3. Bridge for cyclic Module Connection (analog, specialty, and diagnostic modules).
4. Bridge for unscheduled CIP messages to ControlLogix CPUs in that chassis, or to other network bridge modules.

 

[sabre123]

Perfect. Thanks for your help on this, Ken.