ControlLogix & Prosoft module vs ModBus AOI

Brew Chip

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Oct 2013
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I've worked on a handful of projects that relied on a Prosoft module for Modbus comms with other systems (older PLCs, boilers, chillers, much older PLCs) but just recently stumbled across Rockwell's own Modbus AOI for ControlLogix & CompactLogix controllers. Has anyone compared these two options? If the AOI works reliably and doesn't create a performance hit, what's the value of using a Prosoft (or any other gateway device)? 🍺 Cheers
 
It works.

Caveats: fixed 5-transaction count per client and memory use.

I rewrote it to address the above stuff and improved re-connects. Also generalized and streamlined the interface to interoperate with AOIs written for Modbus devices.

You’ll still need a gateway to handle the TCP <-> RTU aspect, if the controller is communicating with such a device: ~$199 from AD.

If the endpoint is a MBTCP device, enjoy not paying for extra hardware, a device circuit breaker, another IP address, and another node burned from the Logix limit the Prosoft unit will charge you.
 
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The logic example from Rockwell prior to the AOI, was not reliable and cumbersome to use. I currently have a mixture of Prosoft cards, and the AOI in use. So far, I have had good luck with the AOI. But....I don't have a lot of data, usually around 10-50 words per client or server, and usually only two connections per PLC.

If you have a lot of connections, need to use word or byte swaps, then the Prosoft pays for itself in the ease of application, and less overhead in for your PLC. A few years ago, I commissioned a system with roughly 120 modbus servers each sending around 1000 words. I used 5 prosoft modules for that one.
 
<self-note to find the program>

There’s a decent program freely available that will let you instantiate as many Modbus TCP servers on your PC as you see fit (same IP, but unique port per). You can then create as many clients as memory permits on the controller and test performance.
 
I have used ProSoft in-chassis for Modbus RTU and TCP. It's nice having the communication handled by the module. Another possibility I used earlier this year for RTU to a boiler burner is the 5069-SERIAL. Setup of that was very nice, done inside the module definition.
 
Thanks for the feedback, everyone. I've been on some projects that are heavy on ModBus and there's no question a gateway is necessary, but it sounds like this is a good option for the lighter comms I'm dealing with this time around.

JeremyM: I'm not sure if you had a different program in mind, but I've used Modbus Examiner to help test & simulate the comms in the past, that was a huge help. I'm not too worried about the 5 connection limit, but I'm curious about your tweaks. What was the re-connect issue you were having?
 

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