A diagnostic device that may be included in a superior-level application, for example as an ActiveX component with a software interface standardized for this purpose. The superior-level application may be a visualization application of a control application or a visualization at the control level. The diagnostic device receives diagnostic data for a field bus from a field bus switching component. The diagnostic data is transmitted via a PLC I/O bus and interfaces provided in the PLC, without the need to parameterize or program either the control application or the visualization application.