Rockwell Automation Logix5000 Controllers Controller Information and Status Programming Manual - Manual (Page 12)

Chapter 1 Connections
If the controller loses communication with a module, data from that device does
not update. When this occurs, the logic acts on the data in ways that may or may
not be correct. You can program the controller to manage faults safely and
efficiently.
Outputs respond to the last, non-faulted state of the controlling inputs. To avoid potential injury and
damage to machinery, make sure this does not create an unsafe operation. Configure critical I/O modules to
generate a controller major fault when they lose their connections to the controller, or monitor the status of
I/O modules.
Example: Loss of Communication
Controller B requires data from controller A. If communication fails between the controllers, controller B
continues to act on the last data that it received from controller A.
If communication with a device in the I/O configuration of the controller does
not occur for 100 ms, the communication times out. If this occurs, you have the
following options.
If you want the controller to Then
Fault (major fault) Configure a major fault to occur on page 13 .
Continue operating Monitor the health of a module on page 13 .
Manage a connection
failure
12 Rockwell Automation Publication 1756-PM015F-EN-P – October 2014