Controlnet Topology

Hi, I have a control logix system with a pair of redundant CPUs, that are to communicate with remote I/O using Controlnet. I have attached a simple layout of the described system. However, in the documents I've seen for Controlnet and reducnacy systems say that at least 2 nodes in addition to the CNBs or the redundant pair is needed. Is this topology not correct? The system as it is hooked up now, is not communicating with the Controlnet modules and I/Os and I wanted to see if this was the reason. I'm not very experienced with Allen Bradley/Rockwell products. Can someone point me in the right direction?

That's a nice layout drawing !

You are correct: ControlLogix Redundancy requires at least two ControlNet nodes on the ControlNet network segment besides the two 1756-CNB or 1756-CN2 Series B modules that are in the redundant chassis, and those devices must have lower node numbers than the 1756 ControlNet bridges in the redundant chassis.

This requirement is related to the Moderator function of ControlNet and the way that the redundant ControlNet bridges switch node numbers during a Primary/Secondary switchover.

The absence of a second low-numbered ControlNet node will only prevent an uninterrupted redundancy switchover; if you were to force a switchover on the system you show, the I/O connections would go to their configured failure state for a few seconds then reconnect.

A system built as you describe should be able to successfully connect and run the remote I/O modules.

Troubleshoot this like any other ControlNet connection issue; look at the LEDs on the ControlNet modules in the redundant and the remote chassis, note the scrolling status messages on the 1756 ControlNet modules, and look at the status messages showing for the ControlNet modules in the I/O tree of RSLogix 5000.

You can get support on this system from your Rockwell Automation distributor, from your local Rockwell Automation office, or from Rockwell Automation Technical Support at (440) 646-3434. A TechConnect support contract is required for most RA support functions.

Thank you very much for your response!
I think I need to check out the configuration with RSNetworx. However, I only have the demo version from the Rockwell website and I'm getting a warning saying I need version 4.00 or higher. Do you happen to know if there is a higher demo version available?

RSNetworx for ControlNet is on version 10.0 now.

Edit: There is a Rockwell Software "downloads" site with 5-to-15-year-old software versions placed there for convenience, sometimes quite a long time ago. There is a link to the real RSI Software Updates site, but it might be easy to overlook if you didn't know how Rockwell Software provides real support and updates.


If you don't have RSNetworx for ControlNet, then the ControlNet network is almost certainly not scheduled, which is why the I/O connections aren't working. A licensed copy of RSNetworx is required to make a ControlNet schedule.

This is the link for where I got the demo software:
http://www.software.rockwell.com/support/download/result.cfm?product=37

It's an older demo version than 4.00.

Hi, I obtained a RSNetworx, and I followed the documentation of cnet-um001 to schedule and configure the system. However, the cnet modules and remote I/O are still not being recognized and there is still the code 16#0204 with yellow triangles next to the modules. Is there something might be missing in the configuration or system that maybe causing those modules to still not be "seen"?

sorry, just to add, the modules themselves are flashing green ok with an "ok" status. It seems to just not be able to connected and configured.

if I'm not mistaken flashing green means the individual module itself is OK but its not seeing the network. Solid green is when its communicating

Yes, that's what it means. I'm trying to figure out why it is not communicating with everything else. I looked in RSLinx and the modules are seen. However, the module on the remote I/O rack is seen at node 44 for some reason. I tried changing the module configuration in RSlogix 5000 and also the scheduling in RSNetworx to match that just to see if it would do anything and It didn't. The modules are still not communicating. Does anyone have any suggestions of something to try?

1756-CNB ControlNet bridge modules have their ControlNet node address set using rotary switches on the top of the module, not with software.

Pop that remote-chassis 1756-CNB out and check out the actual address that the rotary switches are set for.

Ken Roach said:

RSNetworx for ControlNet is on version 10.0 now.

Edit: There is a Rockwell Software "downloads" site with 5-to-15-year-old software versions placed there for convenience, sometimes quite a long time ago. There is a link to the real RSI Software Updates site, but it might be easy to overlook if you didn't know how Rockwell Software provides real support and updates.


If you don't have RSNetworx for ControlNet, then the ControlNet network is almost certainly not scheduled, which is why the I/O connections aren't working. A licensed copy of RSNetworx is required to make a ControlNet schedule.

Click to expand...

Ken

R u saying there are 2 seperate download sites? I am curious as i find it hard to find the real old versions on the download site. I do some lite programming on the side from my full time job and somtimes customers want you to make changes with the same version that they have mostly when they do not have a support contract so i try to keep old versions or that.

Hi All,
Good day!
It is mentioned in the manual and I quote…..
Don’t give the lowest addresses to the redundant chassis pair.
If you give the lowest address to a CNB module in the redundant chassis pair:

• On a switchover, you may temporarily lose communication with I/O modules, produced tags, and consumed tags.
• If you remove the CNB module from the primary chassis while chassis power is on, you may temporarily lose communication with I/O modules, produced tags, and consumed tags.
• If every ControlNet node powers down at the same time (e.g., aplant-wide power loss), you may have to cycle the power to the primary chassis to restore communication.

My question is:
One of our redundant chassis pair is configured to have the lowest node address i.e. (node 1 & 2) and the remote I/O’s are (node 3 & 4). We are experiencing few switchover but ‘till this time no lose of communication. Can you enlighten me? We are using CLX5555 F/W Rev 11.25