Communication
11.3 PROFIBUS
S7-1200 Programmable controller
968 System Manual, V4.2, 09/2016, A5E02486680-AK
A PROFIBUS system uses a bus master to poll slave devices distributed in a multi-drop
fashion on an RS485 serial bus. A PROFIBUS slave is any peripheral device (I/O
transducer, valve, motor drive, or other measuring device) which processes information and
sends its output to the master. The slave forms a passive station on the network since it
does not have bus access rights, and can only acknowledge received messages, or send
response messages to the master upon request. All PROFIBUS slaves have the same
priority, and all network communication originates from the master.
A PROFIBUS master forms an "active station" on the network. PROFIBUS DP defines two
classes of masters. A class 1 master (normally a central programmable controller (PLC) or a
PC running special software) handles the normal communication or exchange of data with
the slaves assigned to it. A class 2 master (usually a configuration device, such as a laptop
or programming console used for commissioning, maintenance, or diagnostics purposes) is
a special device primarily used for commissioning slaves and for diagnostic purposes.
The S7-1200 is connected to a PROFIBUS network as a DP slave with the CM 1242-5
communication module. The CM 1242-5 (DP slave) module can be the communications
partner of DP V0/V1 masters. If you want to configure the module in a third-party system,
there is a GSD file available for the CM 1242-5 (DP slave) on the CD that ships with the
module and on Siemens Automation Customer Support
(https://support.industry.siemens.com/cs/ww/en/ps/6GK7242-5DX30-0XE0) pages on the
Internet.
In the figure below, the S7-1200 is a DP slave to an S7-300 controller:
The S7-1200 is connected to a PROFIBUS network as a DP master with the CM 1243-5
communication module. The CM 1243-5 (DP master) module can be the communications
partner of DP V0/V1 slaves. In the figure below, the S7-1200 is a master controlling an
ET 200SP DP slave:
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