Specifications

PROFIBUS
System Overview
Process or field communication
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Siemens LV 1 · 2007
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DP device types
PROFIBUS DP differentiates between two different classes of
master and various DP functionalities:
• DP master class 1
The DP master class 1 is the central component of PROFIBUS
DP. In a fixed, continuously recurring message cycle the cen-
tral controller or PC exchanges information with distributed
stations (DP slaves).
• DP master class 2
Devices of this type (programming, configuring or operating
devices) are used during start-up, for configuring the DP sys-
tem or for operating the plant while it is running (diagnostics).
A DP master class 2 is able, for example, to read the input
data, output data, diagnostics data and configuration data of
slaves.
• DP slave
A DP slave is an I/O station which reads in input information
and sends out output information to the other peripherals. The
amount of input and output information varies from device to
device but is limited to a maximum 244 bytes per device. The
functional scope of DP masters class 1 and 2 and of DP slaves
can vary. A communications processor can be accordingly
efficient and versatile.
•DP-V0
The DP master functions (DP-V0) are: Configuring, parameter-
izing, cyclic reading of input data and writing of outputs, and
reading of diagnostics data.
•DP-V1
The additional DP function expansions (DP-V 1) enable acy-
clic read and write functions and alarm acknowledgment in
parallel with the cyclic data traffic. These expanded DP func-
tions also include acyclic access to the parameters and mea-
sured values of a slave (e.g. field devices of the process auto-
mation, intelligent operating and monitoring devices). Slaves
of this type must be supplied with comprehensive parameter
data during start-up and while running. The acyclically trans-
mitted data (e.g. parameterizing data) are changed only rarely
compared to the cyclic measured values and are transmitted
with low priority in parallel with the fast cyclic transfer of useful
data. Alarm acknowledgment on the master provides for the
assured transmission of alarms from DP slaves.
• DP-V2
The DP master functions (DP-V2) are: cycle synchronization
and cross data traffic between DP slaves.
• Cycle synchronization
Cycle synchronization is realized through the use of an equi-
distant cycle signal on the bus system. This cyclic, equidistant
cycle is sent as a global control message frame from the mas-
ter to all stations. Master and slaves can thus synchronize their
applications on this signal. For typical drive applications it is
necessary for the jitter of the cycle signal to be smaller than
1µs.
• Cross data traffic between DP slaves
The publisher/subscriber model is used to implement the
cross traffic between slaves. Slaves which are declared to be
publishers make available their input data (equivalent to a re-
ply message frame to their own master) to other slaves, the
subscribers, for them to read as well. The cross traffic commu-
nication takes place cyclically.
© Siemens AG 2007