BECKHOFF BK3000 - Manual (Page 55)

Appendix
BK3xxx/LC3100 55
Combined operation with PROFIBUS DP
and PROFIBUS FMS
(only BK3000 and BK3100)
PROFIBUS is based on numerous recognized national and international
standards. The protocol architecture follows the OSI (Open System
Interconnection) reference model, which corresponds to the international
standard ISO 7498. The architecture of PROFIBUS FMS and the
PROFIBUS DP protocol is shown in the illustration "Protocol architecture of
PROFIBUS FMS and PROFIBUS DP”.
Both versions use the same protocol to access the bus (layer 2) and the
same data transfer technology (layer 1).
Protocol architecture of
PROFIBUS DP and
PROFIBUS FMS
Layers 3 to 6 are not developed in PROFIBUS FMS. Those facilities of
these layers that are necessary for this field of operation have been
grouped together in the lower layer interface (LLI). The LLI is an element of
layer 7.
The FMS (fieldbus message specification) includes the application protocol
and provides a large number of powerful communication services. FMS is
the interface to the application process. The FMS services are a subset of
the MMS services (MMS, manufacturing message specification, ISO 9506)
of the MAP protocol. The complex MMS services have been optimized to
suit the requirements of fieldbus operations and supplemented by the
addition of special functions for administering communications objects and
network management functions.
Layers 3 to 7 are not developed in PROFIBUS DP. The application layer
(7) is also omitted in order to achieve the necessary transfer rates. The
Direct Data Link Mapper (DDLM) provides the user interface with
convenient access to layer 2. The application functions which are available
to the user, the system behavior, and the behavior of the various
PROFIBUS DP device types, are all specified in the user interface.
One particular advantage of PROFIBUS is the ability to operate the
components PROFIBUS FMS and PROFIBUS DP together on a single
bus. For applications which are content with an increased system response
time, the combined operation of PROFIBUS FMS and PROFIBUS DP bus
couplers on a single bus is both possible and advantageous. It is even
possible to operate both versions of the protocol on a single bus coupler
simultaneously. These devices are then described as a "combislave”.