To increase the availability of the system, you can use a second controller with a redundant PROFINET controller combined with CODESYS Redundancy. CODESYS Redundancy acts as a "backend" to synchronize the application on the two controllers. The native PROFINET system redundancy (SR) ensures smooth data exchange with the field devices.
With the PROFINET system redundancy, both controllers each maintain a connection (AR = application relation) to each PROFINET field device which supports S2 system redundancy. One of the connections has the PRIMARY role, and the other connection has the BACKUP role. Here, only the connection with the PRIMARY role transmits valid data. If the connection with the PRIMARY role fails, then it is possible to smoothly switch to the connection with the BACKUP role, which now becomes the new PRIMARY connection, in the shortest possible time. Mixed operation with PROFINET field devices which do not support S2 system redundancy is possible. However, in this case data transmission is briefly interrupted when the connection fails because a complete, new connection is established. PROFINET system redundancy can be extended with other redundancy mechanisms, such as MRP ("line redundancy").