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Message (MSG) instructions are used to control data exchange between these controllers, and each MSG instruction has a data block that holds its configuration and status.
In the SLC, that's an Integer (N) data file or an MG (Message Configuration) data file. In the CompactLogix, it's a MESSAGE datatype.
Both of those have an Error bit that you can examine in your logic to determine that the message has failed.
You can also use logic that examines the Enable and Enabled-Waiting bits if you want to manually override the timeout features in the firmware.
It's a pretty flexible process. If you post some more about the network type you are using and which controller is initiating the message, folks make be able to give you more detailed advice.
