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4.7.6
Connection rules in the PROFIBUS subnet
Introduction
There are a number of rules for configuring and installing cables for PROFIBUS networks to
ensure seamless communication over PROFIBUS. These rules apply to both configuring and
cabling as well as address assignment for the different network nodes.
Connection rules
● Before you interconnect individual nodes in a subnet, you must assign a unique PROFIBUS
address to each node.
● Narrow down the number of nodes by limiting the PROFIBUS addresses to the highest
address in the network.
Tip: Mark the address on the housing of all nodes in a subnet. Then you can always see
which address is assigned to which node in your system.
● Connect all nodes in a subnet "in series". No spur lines may be routed to the PROFIBUS DP.
In addition, integrate the programming devices and SIMATIC HMI devices for
commissioning or servicing in the subnet in series.
● If you operate more than 32 nodes on a subnet, you must use RS 485 repeaters to connect
the bus segments. More detailed information can be found in the description of the RS 485
repeater, see the
In a PROFIBUS subnet, all 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.
This means that when a bus segment contains an 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 10 segments can be connected in a row (max. 9 repeaters).
● At least one terminator must be supplied with 5 V.
To accomplish this, the PROFIBUS DP connector with an activated terminating resistor
must be connected to a device that is switched on.
● Before inserting a new node on the subnet, you must switch off its supply voltage.
The station must be inserted first and then switched on.
When a station is disconnected, the connection must first be deactivated and then the
connector withdrawn.
● The bus line of a segment must be terminated at both ends. This is achieved by switching
on the terminating resistor in the PROFIBUS DP connector at the first and last node and
switching off the other terminating resistors.
SIMOTION D4x5-2
Commissioning and Hardware Installation Manual, 03/2018, A5E33441636B
S7‑300 Automation Systems, Module Data Manual.
Connecting
4.7 Connecting PROFIBUS/MPI
81
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