ProSoft Technology PLX51-PBS, User Manual

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PROFIBUS DP
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PROFIBUS MASTER CLASS 1 (DPM1) OR CLASS 2
(DPM2)
PROFIBUS DP Master class 1 (DPM1)
A class 1 master handles the normal communication or exchange of data with the slaves
assigned to it. This is typically a PLC.
It uses cyclic communication to exchange process data with its associated slaves. The class 1
master sets the baud rate and the slave’s auto-detect this rate. Each slave device is assigned
to one master and only that master may write output data to that slave. Other masters may
read information from any slave but can only write output data to their own assigned slaves.
PROFIBUS DP Master class 2 (DPM2)
A class 2 master is a special device primarily used for commissioning slaves and for diagnostic
purposes. This is typically a Supervisor. It uses acyclic communication over what is known as
the MS2 channel. A DPM2 does not have to be permanently connected to the bus system.
CYCLIC COMMUNICATION
The DP master class 1 cyclically exchanges data with all of the slaves assigned to it. This service
is configured. During the configuration process, master and slave addresses are assigned, the
bus parameters are defined, the types and numbers of modules (in the case of modular
slaves) are specified, user-selectable parameter choices are made, etc.
Before data exchange can take place, the master will send parameterization and configuration
telegrams to all of its assigned slaves. These parameters and configuration data are checked
by the slaves. If both are valid, the master will initiate cyclic I/O data communication with the
slave devices.