Message frozen on Enable

leighigh

Member
Join Date
Dec 2012
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Colorado
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81
I have a read and write message in a 1768-L43 Micrologx5343 they are writing too and reading from a SLC5/05.

The messages are frozen on enable and do not change state or time out, they just sit there I have never seen this before has anybody else.
The customer says the com between the two processors worked before.
I can see the target Processor on links. Any Ideas.
 
Put a AFI in front of the messages.... They will eventually timeout and give you the error message.

This is of course only if your messages instructions are setup with the .err bit or timer to keep trying.
 
so now my other messages that were working have stopped. I will try a complete power down and reboot and let to the plant scream. I hope it works.
 
Would throwing an SVC somewhere halfway through the scanned routines help? Maybe an SVC in the SLC program as well...

Has there been a change to the network infrastructure? A router added, reconfigured, anything like that?

I've never run into this problem either.
 
I powered the PLC down waited a minute powered it back up things are working again.
I have never seen this before. I recommended the customer get a spare PLC on site.
 
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I had a similar circumstance where the 5/05 was in Run mode and everything else was working, but the timer that was used for the messaging was not changing it's ACC value.

The line was being scanned, I put in a test OTE on a branch and it went high. When I cycled power to the machine it started timing correctly. The timer was not used anywhere else, reset or had the ACC written to in the program.

I have also found the 5/05 messages to and reads from another PLC that is in Program mode, so if I want to make sure it is running I have the remote PLC write the heartbeat integer, that is constantly incremented, to an integer the 5/05 reads so both PLC's can time out if the number has not changed in a reasonable amount of time.
 
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I had a Micrologix do that after I updated my RSLogix 500 to version 10 (I think) and made an edit to the program. There was a bug with one of the versions where it would corrupt the messaging files. Sometimes it would work on power-up, other times it wouldn't and all of the messages would stay locked up. Lots of fun trying to figure that one out!

I downgraded the RSLogix back to 9 and re-downloaded the program where I had the messaging issues - they never appeared again.
 
I can't tell what's going on without reviewing the logic in detail (and even then, maybe not).

But I've definitely seen this sort of logic behavior when routines are written to trigger MSG instructions on a timer without considering whether or not they are already enabled. When the destination device doesn't answer right away (or there's a disconnection of a cable or a loss of a switch), the buffers fill up and don't empty out in a reasonable period of time, and they look like they're "frozen".

Always write your logic so that it does not trigger a new MSG until the previous one is complete. Set the .TO bit in order to manually time out a message, if you don't want to wait for the default timeout period.
 
BlueAltezza, that was almost certainly a bug that corrupted the Routing Tables (RIX files) in RSLogix 500 version 10. It's been patched.


My understanding of this issue is that the messages are in the CompactLogix, so of course that doesn't apply.

Yes, there can still be bugs in the CompactLogix controller firmware, but I'd make sure the logic itself is sound before investigating those.
 
Yup; the .TO bit is the only status bit you should ever manipulate in a Logix-platform MSG instruction.

Setting that bit with an OTL instruction will cause the MSG to behave as though it has timed out on its own, with the same error code as an actual timeout.
 

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