Modbus TCP Using 1756-L61 and 1756-EN2T

ticknert

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Join Date
Jul 2018
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Philadelphia
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Hi all,

I've been working on a Modbus TCP project using ControlLogix for a few days now and am hitting a wall. Before I start, I would like to say that we've looked into the Prosoft and other 3rd party modules and the client would prefer to keep it all Rockwell for now.

I'm using the Modbus TCP sample code from Rockwell that ships with the default 4 connections. I'm testing on the first connection, 0, but have not been able to pull information out of the device (a GE Multilin 469). It appears that the socket opens and connects successfully, but then resets when the NoReplyCounter[0] reaches 10.

To me, this means that the connection succeeds but the Modbus device is not responding to the request for information from the 'master'. If anyone has some ideas on where to go from here, that would be great. It could be something as little as changing a bit or two, thank you in advance!
 
You should locate an emulator and use that to see what its being sent. There are a few apps mentioned in other threads. One I have used is "Modbus Register Tester" from Square D.
 
Ahh yes, great point. I saw that at the bottom of the quick start but never got the chance to try it out. I'll do that and report back. Thanks!
 
What your customer is asking is going to cost him/her a lot of time and money (not to mention a lot of frustration on your part). I can't speak to all of the third party solutions but I know that the Spectrum Controls Gateway can be configured and operation (communicating between EtherNet/IP and Modbus TCP/Server) inside of 30 minutes with basic communications running inside of 5 to 10 minutes. It also does not require any software (other than a web browser) or PLC programming other than setting up the registers (Modbus) and Tags (EtherNet/IP). No ladder logic on either end. One of the advantages of that is in the future someone won't have to try to decipher how the ladder logic operates where as using the AB Modbus cheat code will require a huge learning curve in the future when someone has to maintain the system.
At the end of the day all that really matters is that the data is being exchanged.
Having said all of that, I don't want to imply that the Spectrum Gateway is the only way to go (although I think it's the best way to go:) )I.E. I'm not intending this to be a sales pitch for Spectrum. There are a lot of good devices out there almost all of which are simpler to use and more reliable than the Rockwell code which basically cheats it's way to communicate via Modbus TCP.
 
Thanks for the response and recommendation. I'll bring it up today and mention the ease of use - I can definitely vouch for the Rockwell Modbus TCP code being dense.

Do you have any experience with the Prosoft MVI56E-MNET? I know that the client has an existing relationship with Prosoft and has used their products in the past for B&R communication.
 
Thanks for the response and recommendation. I'll bring it up today and mention the ease of use - I can definitely vouch for the Rockwell Modbus TCP code being dense.

Do you have any experience with the Prosoft MVI56E-MNET? I know that the client has an existing relationship with Prosoft and has used their products in the past for B&R communication.

A little bit but only for comparison purposes. Check out the info on the Spectrum Controls web site about the Universal Gateway. It uses a web browser to configure and is very simple to setup and use. If you do search on YouTube for Spectrum Controls Gateway you'll find several videos some of which go through the configuration process.
One other thing worth mentioning is that the Spectrum Gateway supports multiple protocols in one box so you're not locked into Modbus TCP to EtherNet/IP. It gives you/your customer flexibility down the road to add to or change the system.
Now, to be "un-bias", if the customer likes the Prosoft device, I'd look at that as well (but I think you'll find the Spectrum Gateway much easier to use;)).
 
As it was said earlier - take your device out of equation for now.
I recently did a demo for a customer where I had Master code running on one controller and Slave on another.
If you don't have two controllers, then you can use both in your L61 with two EN2T cards.

Please follow Quick Start exactly to get Master working.
Once you get it working, you can reduce polling rate from 10 down to 2 or 3 to make update faster, but it will not be faster than 100ms for one transaction.
 
Try moving your read start register By + or - 1 as modbus can be strange and sometimes one node can start counting at Zero rther than 1. Also have you looked at the request in WIRESHARK to see if its fromated correcly.

Try MDBus https://www.calta.com/mdbus.htm as a similulator
 
I feel for you, had to use that logic in a Compact to a Siemens 1200. Brutal.

I never understood how a ML1400 can do Modbus out of the box, but the higher end products cannot.
 
Thanks for posting your trouble with the Native rockwell solution, i have to install this gateway in my plant soon and i am strongly tending towards the spectrum gateway as Firejo has mentioned (he suggested same to me) it looks so simple that you would be crazy not to go that way.


its not certified by my local agent in Oz at present but should be by end of month.


by comparison the Prosoft GUI is showing its age and definitely needs a GUI upgrade compared to the Spectrum unit
 
I have used the Prosoft module several times and although as said above the GUI could use an upgrade, it is quite simple to use. I have used it to talk to Yokogawa paperless chart recorders, flow meters, batch controllers and older VFDs. It is good if you want a full in-rack solution but in the future I will probably use the Prosoft Gateway. Even though it is not in-rack it looks a lot simpler to use, and could be used for several PLCs at the same time.
 
I have used the Prosoft module several times and although as said above the GUI could use an upgrade, it is quite simple to use. I have used it to talk to Yokogawa paperless chart recorders, flow meters, batch controllers and older VFDs. It is good if you want a full in-rack solution but in the future I will probably use the Prosoft Gateway. Even though it is not in-rack it looks a lot simpler to use, and could be used for several PLCs at the same time.

Are the "Prosoft module" and "Prosoft Gateway" two different devices from Prosoft?
 

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