PROFINET follows the provider/consumer model for data exchange. This means that both the IO controller and IO device spontaneously send cyclic data independently. The following device classes are defined for PROFINET (Figure 1):
IO controller: This is typically the Programmable Logic Controller (PLC) in which the automation program runs. The IO controller provides output data to the configured IO devices in its role as provider and is the consumer of input data.
IO device: An IO device is a distributed IO field device connected to one or more IO controllers via PROFINET. The IO device is the provider of input data and the consumer of output data from the IO controller.
IO supervisor: This can be a programming device (PG), personal computer (PC) or human machine interface (HMI) device for commissioning or diagnostic purposes.
A system unit contains at least one IO controller and one or more IO devices. IO supervisors are usually integrated only temporarily for commissioning or troubleshooting purposes.