Load shared - non-redundant I/O data source - using DIObjects

Both AOS nodes host active and backup engines for each other. If one node fails, the remaining one hosts all active engines for both nodes. The following figure shows System Platform communication drivers with OPC Client or DDE/Suitelink client objects (DI client objects).

When both AOS nodes use the same communication driver to communicate with the PLC, the DI client object in the new active engine refers to the server running in that node when the failover occurs. The DI client objects on each node are configured to point to the local communication driver, leaving the node name blank in the DI client object editor. When a failover occurs, the DI client object in the new active engine will refer to the local existing instance of the communication driver that is currently running in that node.

When the AOS nodes use different communication drivers, both drivers must be installed on each node. One of the communication drivers will provide data to the local active DI client object (i.e. DI1), while the other server feeds data to the other DI client object (i.e. DI2) after the failover.

Use the Redundancy.ForceFailoverCmd AppEngine attribute in a script (in the corresponding DI client object) to trigger the failover in the event of a communication failure with the PLC Network.