Unconditioned Message Instruction

[tsalheiser]

Hello,

We recently upgraded one of our PLC-5's to Controllogixs 5k. Everything has come up and ran fine. Scrolling across the processor I see "Unconditioned Message Instruction".

We have both controllogixs and PLC-5's talking to this processor via MSG reads and writes. We have verified all of them are configured correctly with no errors and all data is passing too and from each fine.

Google searching and looking through the manuals are no help so any help is appreciated. Thank you!

 

[Ken Roach]

That's a pretty cool notification; I've never seen that one before.

Obviously, it's warning you about a MSG instruction that's on an unconditional rung. Search for all the MSG instructions and see how they are coded.

Some programmers do repeating MSG instructions by making the instruction on an unconditional rung then doing a OTU instruction to un-latch the /EN bit later, which causes the unconditional rung to re-enable and re-execute the MSG on the next scan.

While this was traditional in the PLC-2 and the SLC-5/02, and it still works in the PLC-5 and ControlLogix, it has not been a recommended method for decades, mostly because it's harder to troubleshoot.

 

[tsalheiser]

Thanks for the reply Ken!

All of our MSG instructions are on a periodic task set for 100ms. They are all set up like the following:

 

[Ken Roach]

Interesting; thanks for the followup !

Obviously those messages are not "Unconditioned". Are you sure that phrase is not the name of the user program ?

The method of retriggering every MSG with its own enable bit does give you the fastest re-transmission but I don't use it because it also uses up as much communication bandwidth as it can.

ControlLogix Produced/Consumed Tags were a feature developed largely to replace that kind of rapidly-repeating MSG instruction.

 

[Contr_Conn]

Are you sure this is a text and not the "Unconnected Message... "?
I don't recall this message in Logix PLC before - will you be able to post your code?
If not, what version of Logix used?