Networking

5.3Rules 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.

Automation System S7-400

Hardware and Installation

5-7

A5E00850741-01

 

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Siemens S7-400 installation manual Rules for Configuring a Network