SIEMENS
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Siemens PM 21 · 2017
Communication
PROFIBUS
4
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Overview
PROFIBUS – The proven, rugged bus system for
automation engineering applications
The demands of users for an open, vendor-independent com-
munication system resulted in the specification and standardiza-
tion of the PROFIBUS protocol.
PROFIBUS defines the technical and functional features of a
serial fieldbus system with which distributed programmable field
controllers of the low-end (sensor/actuator level) to mid perfor-
mance range (cell level) can be networked.
Standardization according to IEC 61158/EN 50170 provides
future protection for your investments.
Through the conformity and interoperability test performed by
the test laboratories authorized by PROFIBUS & PROFINET In-
ternational (PI) and the certification of the devices by PI, the user
can rest assured that quality and functionality are also ensured
for multi-vendor installations.
PROFIBUS variants
Two different PROFIBUS variants have been defined to fulfill the
wide range of different requirements at the field level:
•
PROFIBUS PA (P
rocess A
utomation) – the variant for
applications in process automation. PROFIBUS PA uses the
intrinsically safe transmission technology specified in
IEC 61158-2.
•
PROFIBUS DP (D
istributed P
eripherals) – this variant, which is
optimized for speed, is tailored especially for the
communication of automation systems with distributed
IO stations and drives. PROFIBUS DP is characterized by its
very short response times and high degree of fault tolerance
and replaces cost-intensive parallel signal transmission with
24 V and the measured value transmission with 0/4 … 20 mA
technology.
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Design
Bus nodes for PROFIBUS DP
PROFIBUS DP distinguishes between two different master
classes and one slave class:
DP master class 1
The DP master class 1 is the central component in
PROFIBUS DP. The central master station exchanges informa-
tion with distributed stations (DP slaves) in a fixed, consistently
repeated message cycle.
DP master class 2
Devices of this type (programming, configuration or control de-
vices) are used during start-up, for configuring the DP system,
for diagnostics or controlling the plant during normal operation.
A DP master class 2 can be used, for example, to read the input,
output, diagnostics and configuration data of the slaves.
DP slave
A DP slave is an I/O device which receives output information or
setpoints from the DP master and sends input information,
measured values or actual values to the DP master in response.
A DP slave never sends data automatically, it must always be
prompted by the DP master.
The volume of input and output data depends on the device and
can be up to 244 bytes per DP slave and transfer direction.
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Function
Functional scope in DP masters and DP slaves
The functional scope can differ between DP masters and
DP slaves. The functional scope is different for DP-V0, DP-V1
and DP-V2.
DP-V0 communication functions
The DP-V0 master functions comprise the functions "Configura-
tion", "Parameter Assignment", "Read Diagnostics Data" as well
as cyclic reading of input data/actual values and writing output
data/setpoints.
DP-V1 communication functions
The DP-V1 function expansions make it possible to perform
acyclic read and write functions as well as processing cyclic
data communication. This type of slave must be supplied with
extensive parameterization data during start-up and during nor-
mal operation. These acyclically transferred parameterization
data are only rarely changed in comparison to the cyclic set-
points, actual values, and measured values, and are transferred
at lower priority in parallel with the cyclic high-speed user data
transfer. Detailed diagnostic information can be transferred in
the same way.
DP-V2 communication functions
The extended DP-V2 master functions mainly comprise func-
tions for isochronous operation and direct data exchange be-
tween DP slaves.
•
Isochronous mode:
Isochronous mode is implemented by means of an equidistant
signal in the bus system. This cyclic, equidistant cycle is sent
by the DP master to all bus nodes in the form of a Global
Control Telegram. Master and slaves can then synchronize
their applications with this signal. The signal jitter between
cycles is less than 1 μs.
•
Slave-to-slave communication:
The "publisher/subscriber" model is used to implement slave-
to-slave communication. Slaves declared as publishers make
their input data/actual values and measured values available
to other slaves, the subscribers, for reading. This is performed
by sending the response frame to the master as a broadcast.
Slave-to-slave communication is therefore a cyclic process.
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Integration
PROFIBUS for SIMOTION
SIMOTION uses the PROFIBUS protocol PROFIBUS DP. SIMO-
TION can be used both as a DP master and a DP slave. The
DP-V0, DP-V1 and DP-V2 communication functions are sup-
ported.
G_PM10_XX_00144
© Siemens AG 2017