Communication between CompactLogix and Modbus protocol Devices

Hi, Anyone can help me?

I need to make compactLogix PLC program to communicate with the modbus device( SEL, Intelligent Motor Protection Relay ) over the modbus protocol.

Is Compact Logix support Modbus protocol without putting a Prosoft Hardware modules ?

I want to communicate compact logix PLC with the modbus devices without the use of any hardware module, by writing the read and write functions for modbus in ladder logic program.

I don't know where to start, Can anyone give me a guideline ? Thank.

Not that i am aware of. Ive asked myself why don't these big name manufactures make their own modules but i guess its a business decision or something else. Another thing you should also figure out is what kind of modbus protocol your modbus devices support, is it Modbus TCP/IP, RTU, etc.... I think prosoft is your best bet but you need to verify and understand what type of modbus protocol your field devices support first.

We always use Prosoft. Pricey but easy.

http://www.prosoft-technology.com/Products/Rockwell-Automation-In-chassis

I very strongly recommend the Prosoft modules or another Ethernet/Modbus RTU bridge device.

ControlLogix and CompactLogix controllers do not have native support for Modbus RTU, Modbus ASCII, or Modbus/TCP protocols.

There are sample programs that implement Modbus via the serial port of the controller; they are included in the Sample programs that are installed along with RSLogix 5000.

This program is also available in the RA Knowledgebase as Answer ID # 42662:

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/42662

In addition there is a document that describes this examples in detail, Rockwell Automation Publication CIG-AP129A:

http://literature.rockwellautomation.com/idc/groups/literature/documents/ap/cig-ap129_-en-p.pdf

While these example programs have been around for about 10 years, and are very well documented, I still don't use them because they consume too much memory and cannot be used with modern ControlLogix and CompactLogix that do not have RS-232 serial ports.

you will save yourself alot of headache if you use something like a red lion datastation plus or a digi one iap, that is if you are dead set against using the prosoft due to pricing.

I agree that using a module as other have suggested is a better approach, but they do have sample code to do modbus TCP on the Rockwell Sample code website, just search for "ControlLogix/CompactLogix Modbus TCP Program" on the sample code website.

I have used this with success, It's not a bridge, only one instrument can be connected to it. Support is great.
http://gridconnect.com/modbus-to-ethernet-ip.html

ProSoft has some newer CompactLogix Modbus modules that are a lot more cost competitive when compared to gateways.

I didn't know about the "Lite" module for the CompactLogix platform. Thanks for the link !

Thank to you all for replies and info,

I looked into sample programs and found that it is too much complicated if compare to logix500.

i wondering why this type of application can be done easily with logix500 controller but not with logix5000 controllers.

I had an old project using Micrologix1400.
I used Msg instruction to communication with Modbus (TCP/IP) devices via Ethernet Switch.The program is simple and get the job done easily.

Now my boss want me to upgrade the same project by using Compactlogix and i found the different story.

No choice, Once i have no budget from my management for external modules, such as prosoft, i need to try with software code first.
Try my luck.

It's a learning experience, I suppose. MicroLogix has some built-in Modbus features and CompactLogix doesn't.

I use MicroLogix 1400 for just one of my machines for exactly this reason; there's another device that requires Modbus/TCP and it's included in the MicroLogix 1400 Series B controller.

Be sure to keep track of the time you spend testing this logic implementation and compare that cost to the hardware cost of the Prosoft module.