The PROFINET Controller is equipped with an internal buffer for diagnostic data. This "shadowing database" is constantly updated in the background (transparent for the user) by alarms sent from the devices and by acyclic services for establishing the connection. In this way, with a minimum delay the actual diagnosis status of all devices is mirrored in the host application and can be evaluated there at any time. Alternatively or additionally, the application can receive the individual alarms (‎CommFB.RALARM‎) or re-read the diagnosis data (‎CommFB.RDREC‎).