ABB S900 Manual page 31

short circuit in one of the two cables does not influence the other cable. In the
following text, the individual cables and the connected PROFIBUS nodes are
referred to as a PROFIBUS line. A logical PROFIBUS structure with a
common PROFIBUS address space is usually called a PROFIBUS trunk. A
trunk or line can consist of one or several segments. Segmentation is done due
to physical limitations of the PROFIBUS, and the number of nodes, the baud
rate, and the cable lengths are taken into consideration. Since the S900
Communication Interface has only one PROFIBUS connector for reasons of
space, cost, and energy balance (Ex), a separate Communication Interface
must be used for each line to achieve line redundancy. PROFIBUS line
redundancy only considers failures of the PROFIBUS line and assumes that
both Communication Interfaces are fully operational. As the S900 is a
PROFIBUS slave, both Communication Interfaces are passive PROFIBUS
nodes (as seen from PROFIBUS), they must not be active on the bus on their
own initiative. Furthermore, for the function within the S900 system, active
and
Communication Interface exchange cyclic or non-cyclic data with the
PROFIBUS master(s) and control the I/O modules on the internal bus (CAN
bus). The redundant Communication Interface, which in broad sense could
also be called passive Communication Interface, communicates with the
cyclic master exclusively for diagnostic purposes of the redundant
PROFIBUS line. For improved scalability and matching to the master system
there are two operating modes available at present.
•
Off (0)
•
Mode 1
As seen from the control system these redundancy operating modes work
according to the single-machine model, i. e. the master/the control system
only has to consider one slave in the engineering for the user data (I/O data)
exchange. The decision for a redundancy toggle is made by the slave itself.
Because of the master-slave relationship the slave cannot diagnose the lines
without the support of the master; therefore, additional functions are used in
the master system depending on the selected operating mode.
The two lines are physically isolated via a voter (RLM01). For the DP master
respectively the DCS the voter is not visible. When the master is transmitting,
both lines are active. For receiving the line that receives the first valid
character is switched through to the master. Thus, a master can communicate
with the slaves of both lines without a connection between the lines. The
3BDD010422R0101
Communication Interface for PROFIBUS DP, CI920
passive Communication Interface are distinguished.
I/O System S900
Active
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