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In any installation it is frequently necessary to adjust device parameters during runtime. For this purpose, PROFIBUS provides communication with acyclic parameter data.


A parameter master, which PROFIBUS calls a class 2 master, can establish a connection with a slave and exchange data acyclically. This is known as MS2.


Several class 2 masters may exist in a network alongside the class 1 master or masters and can simultaneously exchange data with the same slave. Any class 1 master can also simultaneously be a class 2 master.


Any class 1 master that has a cyclic MS0 relationship with a slave can also exchange data with it acyclically as MS1. In addition, an alarm model has been defined. Each slave has a status machine for alarms and checks the variously caused incoming and outgoing alarms, verifying acknowledgement by the class 1 master.  


These protocol extensions for acyclic data exchange are part of the DP-V1 extensions and are optional.