Multiple Access; S900 And Dtm; Diagnostics; Redundancy - ABB S900 Manual

I/O System S900
Communication Interface for PROFIBUS DP, CI920

Multiple access

A separate SAP (Service Access Point) must exist for every non-cyclic link.
In the slave, a buffer must be provided for intermediate data storage. Since
the memory in the slave - or better said in the PROFIBUS ASIC - is limited,
the number of possible simultaneous links is limited as well. S900 provides
one SAP (plus buffer) for the Class_1 master and one SAP (plus buffer) for a
Class_2 master. If the master attempts to set up a second link or a second
Class_2 master is added, the slave will cancel any further communication
setup.

S900 and DTM

The DTM (Device Type Manager) is used as the S900 configuration and
parameterization tool. It can be integrated in stand-alone applications or
engineering tools via a standardized interface (FDT = Field Device Tool). The
FDT interface is not especially designed for the PROFIBUS and only
supports the services for communication setup (MSAC2_Initiate), reading,
writing, and communication interruption (MSAC2_Abort). Thus, the FDT
and DTM do not use the full DPV1 functionality.

Diagnostics

S900 additionally provides all diagnostic information via slots and indices in
a readable form. As a result, it is possible to extend the information content of
the diagnostics far beyond the "standardized" scope. Among the special
features are a time stamp for every event and a ring buffer for historical
diagnostic messages.

Redundancy

PROFIBUS line redundancy

To increase the availability of multi-channel remote systems the
communication link to these remote systems is implemented as a redundant
link. For this purpose usually two PROFIBUS cables are laid via different
routes to the PROFIBUS nodes. This way a redundant bus is established, and
the two PROFIBUS cables are physically isolated, so that the interruption or a
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