Profibus devices communicate using the standardized PROFIBUS DP (Decentralized Periphery) communication profile which defines the rules governing communication.
PROFIBUS communication
At the heart of the communication profile is what is known as the master/slave concept, whereby a master (active communication peer) polls the associated slaves (passive communication peers) cyclically. When polled, a slave will react by sending a response frame to the polling master.
A request frame contains the output data, e.g., setpoint speed of a drive, and the associated response frame contains the input data, e.g., the latest measured value from a sensor. In one bus cycle, the master polls, e.g., exchanges I/O data with, all associated slaves. This polling cycle is repeated as fast as possible.
In parallel with this type of communication, which is described as cyclic and supports the regular exchange of input and output data between a master and its slaves, parameter data, e.g., device settings, can also be transmitted via PROFIBUS.
This action is initiated by the master (typically under user program control) between I/O cycles to read and/or write slave parameter data. This type of communication is referred to as acyclic communication. There can be more than one master on a PROFIBUS system.
In such systems, access rights are passed from one master to the next (token passing). In order to meet the specific requirements of the various fields of application in the best ways possible, the PROFIBUS communication system has been expanded beyond its basic functionality to include a number of additional levels supporting special functions. There are currently three such protocol levels: DP-V0, DP-V1 and DP-V2.