Communication to I/O
A redundant controller establishes a connection to I/O modules in a remote chassis through the
EtherNet/IP™
communication modules in the redundant chassis. Before entering Run mode, a redundant controller requires time to establish the connection to I/O. If this time exceeds 120 seconds, a major controller fault occurs (Type 2, Code 23).Concurrent Communication
Concurrent communication is a feature that enables synchronized, redundant controllers to maintain unicast, concurrent communication with the same I/O devices. Concurrent communication provides seamless failover for any redundant pair of hardware components. A 1756-EN4TR module is required in each redundant chassis for concurrent communication to I/O.
Not all I/O devices support concurrent communication. For concurrent communication system and configuration requirements, see Concurrent Communication.
Logix SIS Concurrent Communication
Redundant controllers that are configured for Logix SIS can exchange safety data with
FLEX 5000®
safety I/O modules via concurrent communication:- Both controllers receive safety inputs and agree on which data to use for each safety task cycle.
- Both controllers send safety outputs and cross-check to verify that the outputs match.
If a fault occurs on one of the controllers, a switchover or disqualification occurs and the other controller continues to execute the safety task alone. Because the concurrent connection is already established, there is no loss of service to the safety I/O module.
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