Multiple Controllers in RSLogix5000


Thread Starter


I have just been informed that we are using at least 2 controllers on a single rack for a controllogix5000 project. I have trawled the interweb and all I get is - yes you can. No instruction on how to configure, do I need to communicate between the cpu's to manage tasks etc.. Just hoping someone else has done this and might have some insight.

Thanks in advance


Kevin Cooper

Yes you can have multiple processors in the same rack, and there is no real configuration issues. Communications between the processors can be achieved just like processors in separate racks: messaging, producer-consumer tags, etc. Here is some information from Allen Bradley:

<b>Moderator's note: it looks like you need a login to access these web pages</b>

If this is not a Redundancy system, the only limit on amount of controllers in the same chassis is the rack size (minus number of communication and other modules when applicable). You still need to calculate total power consumption vs power supply specifications.

With Redundancy system the limit is two controllers in the same rack.

The Logix architecture allows (does not prohibit) configuring multiple owners to the same connection target.
However, the RSLogix 5000 project does not have any source of information about connections configured by other connection originators.

All non-redundant connections can be classified by the relationships of ownership between connection target and connection originator in three groups:
- Owner Connection,
- Listen Only Connection,
- and Input Only (Multicast) Connection.
These are also called connection transport types.

For Input Modules - There can be multiple owners of input modules as long as each owner has selected exactly the same configuration for the input module.

An Input Only connection can be shared between multiple controllers.
Input Only connection continues to receive input data even if the owner connection fails.
The input module will continue to produce its input data even though some of the controllers sharing the inputs have been powered down.

A Listen Only connection can be established only in addition to an Owner connection and only after the Owner connection has already launched.
A Listen Only connection will be closed immediately after the Owner connection closes, which the 'Listen Only' connection monitors.
Even if heartbeat produced for this connection, it will be ignored by I/O target.

For Output Modules - In the case where more than one Owner for the connection was configured the one that established the connection first will control the outputs and configure the target.
Another controller cannot be an Owner of the same Output Module and even input data cannot be consumed by the second controller.

Kevin Cooper

The moderator is correct, I went back and checked and even though the first link has "Access Level: Everyone" you still have to log in. So,to summarize you can have as many NON-REDUNDANT controllers in the rack as there are slots, (as long as you have the power budget). each controller is programmatically separate. you have the ability to communicate between controllers, and even some sharing of local and remote i/o. There is nothing special that needs to be done. You can even plug a new controller in to the rack, while the other controller(s) are up and running with no negative results.

Gerald Beaudoin

We have such a configuration....2 processors in the same rack using produce/consume data exchange between them. One was set up to handle a critical motion application and the other processor handles everything else. In retrospect, it might have been overkill, but it certainly was not a problem to set up. In our case there was no common direct I/O, other than by the produce/consume exchange. Also, last year we upgraded one of the processors to a more recent hardware version and they are no longer even running the same firmware version. Everything continues to play very nicely together as it has for the past 7 years.

Gerald Beaudoin

David Ferguson

First of all, like most things controls "Its easy like a Rubiks cube"I am assuming you know something about Controllogix (basics)....

Yes you can put two controllers in one chassis, in fact if you want you can put 17 of them in a 17 slot chassis (probably wouldn't), when you assign I/O all of the processors can "consume" the inputs and have logic that uses them but only one controller can control and "own" the outputs. So you could have 10 processors using a photo eye and all 10 of them controlling their own outputs based on that eye. Just another way to further divide the processing of things..............then all of the controllers can communicate with each other either with MSG message instructions or using "producer"/"Consumer" etc.

Topic can quickly get deep......

Dave Ferguson
Control Systems Engineer

William Sturm

I have not tried using multiple controllers, but I'm pretty sure the two controllers just share global resources, such as controller tags and I/O. Why do you think that you need two controllers? If it were my project, I would do my best to get it done with one controller. Why add complexity if you don't need to?

Bill Sturm