Connecting
5.2 Networking
SIMOTION C
Operating Instructions, 02/2012
123
Segment
A segment is a bus cable between two terminating resistors. A segment with SIMOTION C
as the master can contain up to 64 slaves. In addition, a segment is limited by the permitted
cable length according to the baud rate (see chapter Onboard measuring system interface
(C230-2, C240) (Page 52)).
Rules for connecting nodes in a subnet
● Connect all nodes in a subnet "in series". In addition, integrate the programming devices
and SIMATIC HMI devices for commissioning or servicing in the subnet in series.
● If you are operating more than 32 nodes in one subnet, you must use RS 485 repeaters
to connect the bus segments (see also the description of the RS 485 repeater in the
S7-
300 Automation Systems, M7-300, Module Data Manual).
In a PROFIBUS subnet, all bus segments combined must have at least one DP master
and one DP slave.
● Use RS 485 repeaters to connect ungrounded bus segments and grounded bus
segments.
● The maximum number of nodes per bus segment decreases with each RS 485 repeater.
That is, if a bus segment contains one RS 485 repeater, the bus segment can contain no
more than 31 additional nodes. However, the number of RS 485 repeaters does not affect
the maximum number of nodes on the bus.
Up to ten segments can be connected in series.
● Switch on the terminating resistor at the first and last node of a segment.
Components
Connect the individual nodes using bus connectors and the PROFIBUS cable, also refer to
chapter Network components for a PROFIBUS subnet (Page 125). Remember to provide a
bus connector with a programming device socket at the ends of the subnet. This will give you
the option of expanding the subnet if required (for example, for a programming device or
SIMATIC HMI device).
Use RS 485 repeaters for the connection between segments and for extending the cable.
Terminating resistor
A cable must be terminated with its own surge impedance to prevent line disturbances
caused by reflections. To this end, activate the terminating resistor at the first and last node
of a subnet or segment (see figure "Bus connector (6ES7...): Terminating resistor connected
and disconnected" in chapter Network components for a PROFIBUS subnet (Page 125)
Make sure that the nodes to which the terminating resistor is connected are always supplied
with voltage during power-up and operation.
