Rockwell Automation 865 Differential Protection Relay - Manual (Page 135)

Communications 7-9
865-UM001A-EN-P – July 2009
Profibus DP
The Profibus DP protocol is widely used in industry worldwide. An
external or internal Profibus module 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 Allen-Bradley 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 more it is not possible to read continuously only
one single data item. At least two data items must be read in turn to
get updated data from the device.
Available Data
SetPointPS will show the list of all available data items for both
modes.
The Profibus DP communication is activated usually for remote port
via a menu selection with parameter "Protocol".