Networking
5-7
AutomationSystem S7-400 Hardwareand Installation
A5E00850741-01
5.3 Rules for Configuring a Network

Rules

Observe the following rules for connecting the nodes of a network:
•Before you interconnect the individual nodes of the network, you must assign to
each node the MPI address and the highest MPI address or PROFIBUS-DP
address.
Tip: Mark the address of each node in a network on the housing. Todo this, use
the adhesive labels enclosed with the CPU. Youcan then always see which
address is assigned to which node in your plant.
•Before you insert a new node in the network, you must switch offits supply
voltage.
•Connect all the nodes in the network in a row.In other words, include the fixed
programming devices and operator panels directly in the network.
Only use spur lines for connecting the programming devices / OPs to the
network which are needed for startup or maintenance.
•If you operate more than 32 nodes in a PROFIBUS-DP network, you must
connect the bus segments via RS 485 repeaters.
In a PROFIBUS-DP network, all bus segments together must have at least one
DP master and one DP slave.
•Youconnect ungrounded bus segments and grounded bus segments via
RS 485 repeaters (see Reference Manual CPU Data, Chapter 10).
•The maximum number of nodes per bus segment decreases with each
RS 485 repeater.This means that if there is an RS 485 repeater in a bus
segment, there may only be a maximum of 31 other nodes in a bus segment.
However,the number of RS 485 repeaters has no effect on 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.
Toensure the bus operates without interference, you should not switch off these
nodes.