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Old April 19th, 2019, 11:43 AM   #1
JLand
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ControlLogix Modbus TCP/IP Master >4 Devices

I have 6 Modbus devices that I need to get communicating with an L72. Rockwell supplies a program that allows one of their controllers to act as a Modbus master, but it only supports 4 devices out of the box. They do have a rung comment that claims more than 4 devices is possible with modification. Rockwell support (understandably) is not useful for using their program like this, outside their specifications.

So far, I have increased array sizes and added tags appropriately, added rungs, and modified labels. I have gone through the code a dozen times over the past few weeks and just can't hack it. I am pointing all my connections to the same device, connections 0-3 are working fine, 4-5 (the ones I added) are not. Disabling one or more of the working connections does not fix either of connection 4 or 5.

My question is, does anyone have experience with this program and can help? Has anyone successfully modified it to work with more than 4 devices? I am at wits end, I am starting to think it was better to just import RA's supplied program twice and run two instances of it in parallel using local tags instead of global tags where necessary.

Any help would be appreciated enormously, thanks. Let me know if there is anything I can do to help with this process.
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Old April 19th, 2019, 02:28 PM   #2
Firejo
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The Spectrum Controls Gateway will do the job and you won't need any ladder logic or messaging of any type in the Logix or the Modbus devices.

https://www.spectrumcontrols.com/pro...ersal-gateway/
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Old April 19th, 2019, 02:30 PM   #3
JLand
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Quote:
Originally Posted by Firejo View Post
The Spectrum Controls Gateway will do the job and you won't need any ladder logic or messaging of any type in the Logix or the Modbus devices.

https://www.spectrumcontrols.com/pro...ersal-gateway/
That looks nice, but only as a backup, as a programmatic solution is more inline with what the budget allows. Thanks, I will keep it in mind.
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Old April 19th, 2019, 03:14 PM   #4
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True however you might spend more cost in time creating/editing the logic than the cost of the Gateway.
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Old April 19th, 2019, 05:21 PM   #5
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I am familiar with this code and would not recommend you to try to make changes.
There are multiple places in the Master code that have number of connections and transactions hard coded instead of been a parameter through the tag.
You can go rung by rung and see if there is boundary check.
My recommendation is to use Prosoft module.
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Old April 19th, 2019, 06:35 PM   #6
harryting
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Quote:
Originally Posted by Firejo View Post
The Spectrum Controls Gateway will do the job and you won't need any ladder logic or messaging of any type in the Logix or the Modbus devices.

https://www.spectrumcontrols.com/pro...ersal-gateway/
Interesting, they are getting in on this game as well. The protocols supported and # of ports supported is still on the short side compared to RedLion's Edge though. Edge can act as OPC UA server and MQTT, for example not to mention the dreaded DNP3 that's common in my world.
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Old April 19th, 2019, 06:47 PM   #7
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Interesting, they are getting in on this game as well. The protocols supported and # of ports supported is still on the short side compared to RedLion's Edge though. Edge can act as OPC UA server and MQTT, for example not to mention the dreaded DNP3 that's common in my world.
There is more to come in future firmware releases (which will be field up-gradable). I'm not familiar with the Red Lion product however I can say that Spectrum's Gateway supports all of the listed protocols in one version and you can use them simultaneously (I.E. EtherNet/IP and Modbus/TCP via the same Enet port at the same time) and it doesn't require any software to configure (just a web browser).
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Old April 22nd, 2019, 12:04 AM   #8
rdrast
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Seriously, the AB Modbus code is horrendous. It is also HUGE. Using a dedicated gateway probably ends up being much cheaper then upgrading an AB CPU for more memory.


Use a gateway. Spectrum's is awesome, Real Time Automation also makes excellent ones. No hassle, no fuss, no sucking up memory, scan time, no problems with large numbers of end devices...
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