6.2 Communication protocols
6 Communication
Technical description
128
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VM55.EN005
6.2.3.
Profibus DP
The Profibus DP protocol is widely used in industry. An
external VPA 3CG is required.
Device profile “continuous mode”
In this mode the device is sending a configured set of data
parameters continuously to the Profibus DP master. The
benefit of this mode is the speed and easy access to the data in
the Profibus master. The drawback is the maximum buffer size
of 128 bytes, which limits the number of data items transferred
to the master. Some PLCs have their own limitation for the
Profibus buffer size, which may further limit the number of
transferred data items.
Device profile “Request mode”
Using the request mode it is possible to read all the available
data from the VAMP device and still use only a very short
buffer for Profibus data transfer. The drawback is the slower
overall speed of the data transfer and the need of increased
data processing at the Profibus master as every data item must
be separately requested by the master.
NOTE! In request mode it is not possible to read continuously only one single
data item. At least two different data items must be read in turn to get
updated data from the device.
There is a separate manual for VPA 3CG with the code
VMVPA.ENXX available for the continuous mode and request
mode.
Available data
VAMPSET will show the list of all available data items for both
modes. A separate document “Profibus parameters.pdf” is also
available.
The Profibus DP communication is activated usually for remote
port via a menu selection with parameter “Protocol”. See
chapter 6.1.