ILX56-PBS
PROFIBUS DP
ControlLogix® Platform
User Manual
Page 67 of 87
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.
Acyclic communication
In addition to the cyclic data exchange, the PROFIBUS protocol has the option of acyclic
communication. This service is not configured. There are 2 different communication channels
possible between the requested master and the slave:
o
MS1 channel
(MS1 connection): can only be established if cyclic data
exchange is taking place between that master (DPM1) and the slave
o
MS2 channel
(MS2 connection): is possible with several masters
simultaneously, but the connection must be established explicitly by the master.
Acyclic reading and writing of data requires an established MS1 or MS2 connection.
For the MS1 channel, 3 conditions must be satisfied:
o
The slave device must support the MS1 channel (key
C1_Read_Write_supp
at
1 in the GSD file)
o
The DPV1_enable bit must be set during the parameter assignment
o
Data exchange is taking place
For the MS2 channel, the connection must be explicitly initiated by the master. The maximum
number of possible MS2 connections to the slave must not be reached. The connection can
be closed by either the master or the slave device.
Topology of PROFIBUS DP
PROFIBUS devices are connected in a bus structure. Up to 32 stations (master or slaves) can
be connected in one segment. The bus is terminated by an active bus terminator at the
beginning and end of each segment. Both bus terminations must always be powered. When
more than 32 stations are used, repeaters (line amplifiers) must be used to connect the
individual bus segments.
