Siemens SENTRON VL Series

Introduction and overview
1.2 Bus systems
3WL/3VL circuit breakers with communication capability - PROFIBUS
System Manual, 03/2011, A5E01051353-02
13
The following figure shows communication on PROFIBUS:
● Token passing between the available masters
● Polling between master and slave nodes
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Figure 1-1 Communication on PROFIBUS
The figure above shows an example with three master modules and seven slaves. The three
master devices form a logical ring. The token is controlled by the MAC (media access
control). It generates the token in the startup phase and checks if actually only one token
circulates in the logical ring.
Master classes
Each slave that communicates cyclically via PROFIBUS DP is assigned to a class 1 master.
Cyclic data traffic takes place in accordance with the DP standard profile (DPV0).
Master class 1 A class 1 master is used primarily for performing automation tasks. In
addition to cyclic data exchange, a class 1 master can also establish an
acyclic communication connection with its slaves and thus make use of the
expanded functions of a slave.
Master class 2 A class 2 master is especially suitable for commissioning, diagnostics and
visualization tasks. It is connected to PROFIBUS DP in addition to the class
1 master and can access slaves via acyclic services and exchange data,
provided the slaves permit it.