A client request addresses objects in the Computational Model, defined by device name and attribute name parameters. This de-coupling makes the FEC software portable. The PIOser thread Network Agent receives client requests using an in-house developed protocol based on Ethernet, and either stores them to the client request queue, or produces client replies with error indication. The List Handler thread extracts client requests from the queue, and processes device lists by calling the Computational Model and communicating with the Field-Bus Driver. If defined as such, client requests are initially scheduled for the repetitive execution.
Incorrect lists result in client replies indicating an error.
The Scheduled List Execution thread executes repetitive defined lists and produces client replies. The Field-Bus Driver provides a single interface for various types of field access. It accepts requests in the form of field lists, which consist of field cells containing field operations. The routines, implementing procedural interfaces between three sub-domains, consist of a set of routines for translating device cells to field cells, and translating results back to the device cell form. In this way, en bloc field bus access per defined list is introduced, reducing multiple driver call overhead where possible.