Configuring a Network

Subnets

You can connect an S7-400 device to various subnets:

• Via Simatic Net CP Ethernet to an Industrial Ethernet subnet

• Via Simatic Net CP PROFIBUS to a PROFIBUS-DP subnet

• Via the integrated MPI interface to an MPI subnet

• Via the integrated PROFIBUS-DP interface to a PROFIBUS DP subnet

Same Configuration

We recommend you use the same bus components as for a PROFIBUS DP network configuration when configuring an MPI network. The same configuration rules apply.

Multipoint Interface (MPI)

This interface of the CPU uses a Simatic S7-specific protocol for the

communication with programming devices (by means of STEP 7), operator panels, and other S7 CPUs. The bus structure corresponds to PROFIBUS.

Configuring Communication

In order that the individual nodes of an MPI or PROFIBUS-DP network can communicate with each other, you must assign MPI or PROFIBUS-DP addresses to them. The Manual Configuring Hardware and Communication Connections STEP 7 describes how to assign these addresses and what you must take into account.

All the CPU-related data you need to know to configure communication can be found in the Reference Manual CPU Data.

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5.2 Fundamentals

Station = Node

Declaration: All the stations you connect in a network are referred to as nodes in the following.

Segment

A segment is a bus cable between two terminating resistors. A segment can contain up to 32 nodes. Furthermore, a segment is limited by the permissible cable length according to the transmission rate.

Baud Rate

The baud rate (transmission rate) is the speed at which data is transmitted, expressed in terms of bits per second.

• Baud rates of 19.2 kbps to 12 Mbps are possible for interfaces of the type MPI/DP.

• Transmission rates of 9.6 kbps to 12 Mbps are possible for interfaces of the type PROFIBUS-DP.

Note

If you change the parameter assignment of the MPI/DP interface transmission rate, the new transmission rate remains set even after memory reset, voltage failure or removing/inserting the CPU.

Connectable Nodes

MPI PROFIBUS DP

Programming devices (PGs) Programming devices (PGs) Operator interfaces (SIMATIC-OP),

WinCC Operator panels (OPs)*

S7-400 PROFIBUS-DP master, PROFIBUS-DP slaves

S7-300 PROFIBUS-DP slaves

* Not recommended in DP operation

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Number of Nodes

MPI PROFIBUS DP

127 127 *

(default: 32) of which: 1 master (reserved)

1 PG port (reserved) 1 PG port (reserved)

125 slaves or other masters

* Observe the CPU-specific maximum numbers in the Reference Manual CPU Data

MPI/PROFIBUS-DP Addresses

In order for all nodes to be able to communicate with one another, you must assign them an address:

• In the MPI network, an MPI address

• A PROFIBUS-DP address in the PROFIBUS-DP network

Default MPI Addresses

The following table shows the default MPI address and the max. MPI address with which the devices are shipped:

Node (Device) Default MPI Address Default Highest MPI Address

Programming device 0 31

OP 1 31

CPU 2 31

Note

If you change the parameter assignment of the highest MPI address of the MPI/DP interface, the new address remains set even after memory reset, voltage failure or removing/inserting the CPU.

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Rules for MPI Addresses

Observe the following rules before assigning MPI addresses:

• All MPI addresses in an MPI network must be different.

• The highest possible MPI address must be equal to or higher than the highest actual MPI address and must be set to the same value for all nodes. (Exception:

connecting a programming device to two or more nodes.) PG / OP -- Module communication without MPI

If one of the programming devices or operator panels connected to a multipoint interface (MPI) communicates with an S7-400 module which does not have an MPI connection (for example, SIMATIC NET CPs, FM 456 etc.), this module can be reached via the CPU to whose MPI the programming device or operator panel is connected. In this case, the CPU simply acts as an intermediary for the transfer.

This type of connection between a programming device or operator panel and a module only communicating via the communication bus occupies two connection resources in the CPU.

CPU CP or FM

MPI

C bus PG or OP

Two connection resources occupied in the CPU

S7-400

Figure 5-1 Communication between Programming Device/Operator Panel and a Module without MPI

Maximum Number of Connections via MPI

When configuring the connections of a CPU 41x via MPI, remember to include the PG connection in the maximum number of possible connections.

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PG Access

A CPU exchanges data with other systems using communication mechanisms, for example with other programmable controllers, with operator interface stations (OP, OS) or with programming devices (see Figure 5-2).

CPU

SIMATIC NET

MPI

PG OS PLC

PG OS Slave

PG OS PLC

DP network

Figure 5-2 Data Exchange

Process communication, including communication services for data exchange between programmable controllers (PLC - PLC) and between programmable controllers and operator interface stations (PLC - OS/OP), has priority in CPUs over communication between programming devices and CPUs.

The CPUs have different characteristics. One of these characteristics is their communication performance. If the communication resources of a CPU are occupied completely by process communication, this can severely hamper access to the CPU from the programming device.

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