Control Logix IO not Responding

whussain6

Member
Join Date
Oct 2013
Location
Newcastle
Posts
108
Hi Engineers,

I have two PLCs talking on Ethernet through a switch(Moxa). I am transferring data between two (via messages) and it has been working for ages till today.

The data transfer is still working but on my main PLC which has got message instruction, under the IO tree it shows exclamation mark on remote module with error code 16#0203 Connection Timeout.

moon2:

Not sure why the messages are successful even when the module says timeout.

On remote PLC I have the Main PLC in its tree which has no error.

Left is Main PLC and Right is Remote PLC.

IO Not Responding.jpg
 
Well someone been playing with network security. making it more secure. But if it has been affected by that then the messages should have stopped the data transfer. By the way could not open the link you posted.
 
Here is what I would try:
-cycle power to both PLC's
-cycle power to the Moxa switch
-try a different Moxa switch if you have a spare one available
 
someone been playing with network security.

This is going to be a good opportunity for your network administrators to learn how to cooperate with the automation system engineers.

Are these controllers on the same subnet, or on different sides of a router ?

My guess is that the network administrators have enforced some timeouts or blocked comms that allow controllers to talk to one another.

A common example is when a router is configured to block Multicast traffic, but two controllers rely on that for Produced/Consumed Tags. I can't tell if that's the case from just these screenshots.
 
Edit: I looked more closely and see that the left-side controller has a "Rack Optimized" connection to the remote 1756-ENBT chassis that contains the right-side controller.

That would create a cyclic I/O connection, and maybe it would do it with Multicast (you would have to look more closely to see). That's commonly blocked by routers.

The right-side controller has a connection type of "none", which would not create a cyclic I/O connection.

In general, you don't need a Rack Optimized connection unless you're communicating with discrete I/O modules in that chassis. The left-side controller might only to have the right-side controller in the I/O tree to create a MSG instruction target or a Consumed Tag source target.
 
Sorted

Thanks Ken

You are right 'Rack Optimization' removed and it all works.

Because the router was open with no restrictions before and now we are making it secure and putting restrictions etc which caused this. But disabling Rack optimization solved the issue.

Thanks again
 
The left-side controller might only to have the right-side controller in the I/O tree to create a MSG instruction target or a Consumed Tag source target.

No controllers need to be put into the I/O tree for messaging, because there is no need to maintain a "connection", as is the case with Produced/Consumed tags.

Unless the message is cached, a connection is established, the message is transferred, and the connection is broken

The path to the target can be expressed explicitly, so there's no need for it to be in the I/O tree for selection. This can be a god-send on large networks with many messages being used.
 

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