MESSAGE Statement AB CompactLogix Controller

Hello,
I'm wanting to read Modbus registers from a Centurion controller back into the
1769-L32E CompactLogix Controller using the "Message" Data Type command.

I know I have to have some type of modbus PLC card installed, but my question is how do i configure the logix inside the PLC to read these modbus registers?

I have not used the message statement to read from another device & if anyone has any experience with it I would greatly appreciate any help or advise you could give me


Thanks,

Do you need to use Modbus RTU (serial), or Modbus/TCP (Ethernet) ?

First, the MSG instruction doesn't support any Modbus protocol natively in the CompactLogix.

Second the 1769-L32E doesn't support the "raw sockets" feature you would need to use application-specific logic inside the controller to use Modbus/TCP. It does support the serial version of that application-specific logic, but it's complex and difficult to use.

I would use a third-party network gateway device, like the Digi One IAP or a device from RTA Automation.

There are chassis-mounted Modbus modules from Rockwell and Prosoft, but I prefer the network devices.

We have used this unit - works very well!

https://www.anybus.com/products/gateway-index/specific-gateways/ethernet-ip-linking-devices/detail/ethernet-ip-to-modbus-tcp-linking-device

Thanks guys for the help
The anybus device looks very user friendly

After watching the video, it seems you add any
Register that you are wanting to read from the
Modbus device into your Compact Logix PLC

I’ll definitely try this device out, thanks again for your feedback!!

After doing some research most of our Modbus filed devices are Modbus RTU & some sites already have a 1769-sm2 PLC card installed, I called Anybus tech support and there device will not work with our setup because our devices are not Modbus/TCP and are PLC are not V21 or higher.


1. Has anyone had any experience with these 1769-SM2 Modbus/RTU cards?
2. How to configure the logix to read certain modbus registers from the end device? Is the "Message" command used?
3. How to configure the card for Baud rate, stop bits,....etc


thanks,

AB has sample code to use a ControlLogix for Modbus.
Go here http://search.rockwellautomation.com/search?client=samplecode&oe=UTF-8&ie=UTF-8&output=xml_no_dtd&proxystylesheet=samplecode&site=sample_code&getfields=*&lang=en&hl=en&sort=date:L:d1&wc=200&wc_mc=1&ud=1&filter=0&q=modbus

It's quite complicated tho and no guarantees it will work.

i use the Prosoft cards all the time and they work great. But I am only using them to talk to flow meters and Yokogawa chart recorders.

Yeah it does look complicated

I would have though reading modbus addresses into the PLC wouldn't been this complicated

I appreciate the help

I would have though reading modbus addresses into the PLC wouldn't been this complicated

Click to expand...

You can thank Group Schneider and their "Solaia" patent dispute for why it's so hard to use Modbus with Rockwell products. Folks have very long memories.

But back to the issue; the 1769-SM2 isn't too difficult to use. Read the user manual, and remember that it was designed to poll a handful of Holding Registers from AC drives, and you should be able to get it going.

Ken Roach said:

You can thank Group Schneider and their "Solaia" patent dispute for why it's so hard to use Modbus with Rockwell products. Folks have very long memories.

Click to expand...

Way OT, but you've piqued my interest. Care to share the story?

You can read a lot about it by Googling "Solaia 318 OPC Rockwell Schneider".

In short, Schneider Electric sold a patent regarding OPC-like technology to a "patent troll" law firm. I like how the OPC Foundation put it: "The '318 patent is as applicable to OPC as it is to a recipe for gumbo".

That firm expertly used litigation against major companies who used OPC with Rockwell products to bully them into settlements to buy "licenses" for the technology. Those companies were then encouraged to in turn sue Rockwell Automation to recoup their payments.

It took years, and millions of dollars in legal fees, to eventually get a court to rule that the patent was inapplicable.

For me, where the mistrust of Schneider comes in is that the judge in the final ruling learned that Schneider had sold the patent to Solaia for a dollar, with the explicit agreement that they would pursue only Rockwell customers, not Schneider customers.

Rockwell does not trust Schneider not to do something similar with Modbus, a technology to which they have a far better claim than they ever did to OPC, and for which Modbus.org could be turned into a vehicle for their endeavors.

There's also the matter of agreements with Prosoft for their creation of Modbus products for old PLC/SLC systems, and the exception of MicroLogix and SLC support.

But at the heart of it, Rockwell Automation doesn't trust Schneider Electric, and neither do I.

Hey Guys,
I'm revisiting this question in hopes to get some feedback on some hardware to interface to an existing modbus RTU controller.

just to refresh, I have a Allen Bradley 1769-SM2 Modbus RTU card that was setup before my time in the department to read a few Modbus registers from a Centurion contoller.

When this was setup there were some message statements configured to read a range of registers from the modbus controller and then a custom Add-On-Instruction built to make sense of these registers that was read.

Now that I'm trying to read more registers from this controller and troubleshoot communication issues to them, to me it just seems the process is more difficult than it should be. Maybe because I'm having trouble understanding the message read instruction & making sure I'm connecting to the correct modbus node because these are RS485 and there daisy chained all coming into the same 1769-SM2 card.

I do appreciate if someone had a link to help me better understand the message read instruction and the process of reading modbus RTU registers into a Compact Logix 1769-SM2 card.

I have read these Modbus registers just fine in previous projects into our SCADA software by just using a serial RS-232 interface to Ethernet device convertors, but this data needs to come into the PLC.

I found a device made by RedLion that will allow the read of 5 modbus protocols simultaneously to the controller, but its a $1000 per.

Here is a link to the modbus controller I'm trying to read registers from
Centurion-C4

Is there any other hardware out there cheeper to accomplish this?

thanks

https://www.youtube.com/watch?v=EnUIj-ShAYk

Weintek Controller might be a solution.

You might be able to use something like this to convert the Modbus RTU into Modbus Tcp and then use the anybus.

http://www.adfweb.com/home/products/modbus_TCP_RTU.asp?frompg=nav3_8&loc_phy=9022672&k001=e&en-k1=modbus%20rtu%20to%20modbus%20tcp&d=c&g=18226497969&pos=1t3&gclid=EAIaIQobChMI_J2-y6-A2wIVAylpCh0Rzg2aEAAYAyAAEgJF1fD_BwE

Ones_Zeros said:

I found a device made by RedLion that will allow the read of 5 modbus protocols simultaneously to the controller, but its a $1000 per.

Here is a link to the modbus controller I'm trying to read registers from
Centurion-C4

Is there any other hardware out there cheeper to accomplish this?

thanks

Click to expand...

Any Red Lion HMI can do this, even the lowly G304K2 which sells for about $400. I have done some pretty complicated protocol conversion with that little touchscreen, but it might be better to go with their newer CR1000 series which is about the same price. If your application has or will call for an actual HMI, then pick the appropriate size and use it for both HMI and protocol conversion.