Allen Breadley PLC5/40E communication with Controllogix 1756 IO's

Adil.saleem

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Oct 2018
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Lahore
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In one of my project, end-user wants to connect Controllogix 1756 IO's with PLC 5/40E controller on DH+ protocol. 1756 DHRIO card is installed in 1756 IO chassis and a "EtherNet/IP to Allen Bradley Remote I/O or DH+ Gateway" is installed in 1756 IO cabinet.

My question is that, is it possible to connect 1756 IO's with PLC 5 controller on DH+ protocol?

if it is possible, what modifications are required in PLC 5 program to define 1756 IO's?

Is it possible to implement this solution on running plant or i need shutdown?
 
Welcome to the PLCTalk forum community !

The network and control architecture you have described is not possible.

First, a common misunderstanding: Data Highway Plus (DH+) and Allen-Bradley Universal Remote I/O (RIO) are different protocols.

They run on the same physical interfaces and use the same cable types, and many devices (like the 1756-DHRIO module) can be software-configured to run either protocol.

But DH+ is a peer-to-peer messaging protocol, and RIO is a master/slave I/O transport protocol. You can never connect I/O devices to a DH+ network.

Second, the functionality of 1756 series I/O modules and the 1756-DHRIO module do not support what you describe. 1756 I/O can never directly be "slave" devices to a PLC-5 on any protocol, and the 1756-DHRIO does not support an "adapter" mode that would make it behave like a 1771-ASB RIO adapter for a PLC-5 style I/O chassis.

It is possible to exchange data between ControlLogix CPUs and PLC-5 CPUs in various ways (including the RIO and DH+ protocols), but not the way you have described.

What is the overall goal of this system expansion/modification ?
 
Ouch.
You can put a controller in the 1756 rack, even one of the old 5550's would work, and MSG back and forth, but that isn't going to be fast... it might be fast enough depending on the application.
I'd seriously just dump the PLC5 rack; you would probably come out ahead getting rid of the 5, and if you have to keep the IO intact, use the 5 rack with an RIO adapter, controlling it from the Logix rack.
 
Ouch.
You can put a controller in the 1756 rack, even one of the old 5550's would work, and MSG back and forth, but that isn't going to be fast... it might be fast enough depending on the application.

I can confirm that it's not fast... Currently working on a project using exactly a PLC5 messaging to a CLX and the update times are pretty slow.
 
I very strongly recommend against a system that attempts to replicate the function of an I/O network by using a peer-to-peer network and a controller.

At the most, make the ControlLogix system in charge of the local devices that its I/O modules are connected to, and interlock the appropriate amount of data with the master system.

I'm doing that right now; I have a set of modern EtherNet/IP connected servos that will connect to a ControlLogix, which will exchange MSG instructions with the servo "go" and status info with an old SLC-5/05 that previously connected to the obsolete servos directly.

But I'm not approaching it by making the ControlLogix work like a dumb I/O server; it's in full control of the servos and the associated mechanisms, and only takes its setpoints and interlocks from the master controller.

Most retrofits like this go the other way around; the ControlLogix takes over as the main CPU and treats the old 1771 I/O as slave devices on RIO or ControlNet.
 
We did it a long time ago... it was the first jog I had Tim do for me, we did a peer to peer and he also wrote everything in the CLX to control the SLC once we put the CLX as the master, it worked for a just a temp before I wanted to go live and had a weekend for a shutdown and restart, I had the CLX running everything new then did the swap

The only issue was it took a few months before we went live and I forgot about the changes made in the SLC needed to be updated in the CLX also

Sounds like a good time to upgrade
 
Thank roach for your reply and recommendation.


if i install controllgix controller in the RIO cahssis then what would be the communication architecture between PLC5 controller and RIO rack? Please note that PLC5 is the master controller for the plant and end-user don't want to upgrade to controllogix at this stage.

The distance between RIO chassis and PLC5 controller is more than 2Km. So, I need a media converter, because fiber is already layed between the two buildings.

what media converter i need to use for this communication.
 
...if i install controllgix controller in the RIO cahssis then what would be the communication architecture between PLC5 controller and RIO rack?...

This opens the possibility of using a 1756-RIO (different from -DHRIO) module to facilitate a Remote I/O connection where memory in the ControlLogix processor can appear as a "remote rack" to the PLC-5 with mapped I/O and RIO block transfers. You would move the 1756 module data into this shared memory at an appropriate rate (e.g., every CLX processor scan).

However, the 2 Km could be a problem. I am not familiar with RIO extenders
 
if i install controllgix controller in the RIO cahssis then what would be the communication architecture between PLC5 controller and RIO rack? Please note that PLC5 is the master controller for the plant and end-user don't want to upgrade to controllogix at this stage.

The distance between RIO chassis and PLC5 controller is more than 2Km. So, I need a media converter, because fiber is already layed between the two buildings.

what media converter i need to use for this communication.

Reasons like this is why I have walked (or ran) away from jobs and told the customer I can not help them on this project... the only way to do this job is a hourly rate as it will be a huge headache
 
Check out SoftPLC's Smart Gateway. It can look like RIO racks to the PLC-5 and then drive the 1756 I/O via Ethernet. Speed would be limited by the RIO limitations. You shouldn't need to modify the PLC-5 logic, unless the new I/O is added/different from what you had before.
 

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