I was talking yesterday with Schneider Electric and they were mentioning that it’s possible to read the status of the system bits and Words (%S and %SW) provided you were using the UMAS protocol. Apparently, this is a special protocol that sits on top of the Modbus protocol, but it’s propriety for some crazy reason.
Can Ignition make use of this protocol by any chance? Or is there a way to directly read those system bits without having to map them to memory registers?
I ask because I’d like to get the %S12 bit (PLC running) status, but when the PLC isn’t running then it doesn’t update the status of the memory coil 
We don’t know anything about this protocol. You’ll have to stick to what you can get through regular Modbus.
This is a very old thread, but has UMAS been considered again for ignition? OFS is the only OPC Server that supports UMAS and thus reading symbolic tags from Schneider PLCs. It would be great if others could do this too.
No, even if it weren't old and obscure, proprietary and undocumented protocols are not generally up for consideration.
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If you can get Schneider to cough up a specification, I'd be happy to review it for inclusion in my alternate driver.
@pturmel I have been playing around with umas in the plc4x project, and have been able to get it working on a simulator ( at least read support anyway) If you are interested in developing a driver for it, it might be a good starting point.
There's also this series of articles by somebody who reverse engineered parts of it: Liras en la red: The Unity (UMAS) protocol (Part I)
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Yes that is super helpful
I'd also like to add that the ability to read symbolic tags out of Schneider PLCs even if it is only the M580 series would be a significant benefit especially from a maintenance perspective to a large install base in Australia. After many years of neglect (2009-2015) OFS from 2016 onwards has been worked on and updated constantly by Schneider electric.
I didn't find either link very helpful in the sense of making a driver I could stand behind. If someone gets Schneider to cough up a proper spec, I'd be interested.