According to the specification developed by the “Fieldbus Foundation”, control of the communication processes within the fieldbus is performed by two types of transmission:
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Clocked data transmission: This mainly controls tasks which are evaluated as time-critical. A fixed processing schedule is set up to perform execution of the resulting tasks in due time and without access problems. This schedule is created by a system administrator during configuration of the bus system in accordance the the FF specification. During the clocked data transmission, all devices run synchronized in time, whereby the point in time and the sequence are specified in advance. This is also known as a deterministic system.
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Non-clocked data transmission: Here, parametrization and diagnosis especially takes place within the communication control. After all, transmission of this information and data must be possible when it is required. However, the transmission of the device parameters and the diagnosis information is not time-critical, i.e. acyclic, so that with Foundation FB the non-clocked data transmission takes place exclusively in the time gaps of the clocked transmissions.