Siemens Automation System S7-400 - Manual (Page 105)

Networking
5-7
Automation System S7-400 Hardware and 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. To do this, use
the adhesive labels enclosed with the CPU. You can 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 off its 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.
• You connect 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.
To ensure the bus operates without interference, you should not switch off these
nodes.