Wiring the S7-400
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, Chapter 11).
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.
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Data Packets in the MPI Network
Observe the following feature in the MPI network:
Note
If you connect an additional CPU to the MPI network during operation, data may be lost.
Remedy:
1. Disconnect power from the nodes to be connected.
2. Connect the nodes to the MPI network.
3. Switch on the nodes.
Recommendation for MPI Addresses
Reserve MPI address “0” for a service programming device and “1” for a service OP, which will later be briefly connected to the MPI network as required. Thus you assign different MPI addresses to the programming devices / OPs incorporated in the MPI network.
Reserve MPI address “2” for a new CPU. You thus avoid the duplication of MPI addresses after a CPU with a default setting has been installed in the MPI network (for example, when replacing a CPU). Thus you assign an MPI address higher than “2” to all CPUs in the MPI network.
Recommendation for PROFIBUS-DP Addresses
Reserve PROFIBUS-DP address “0” for a service programming device, which will later be briefly connected to the PROFIBUS-DP network as required. Thus you assign other PROFIBUS-DP addresses to all the programming devices
incorporated in the PROFIBUS-DP network.
Components
You connect the individual nodes via bus connectors and the PROFIBUS-DP bus cable. Remember to provide a bus connector with PG female port for nodes into which a programming device may be plugged if required.
Use RS 485 repeaters for the connection between segments and for extending the cable.
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Terminating Resistor on the Bus Connector
on off
Terminating resistor switched off
on off
Terminating resistor switched on
Terminating Resistor on the RS 485 Repeater
DC 24 V
L+ M PE M 5.2
A1 B1 A1 B1
A2 B2A2 B2 SIEMENS RS 485 REPEATER
ON ON
Terminating resistor for bus segment 1
Terminating resistor for bus segment 2
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Example: Terminating Resistor in the MPI Network
The figure below shows where you have to connect the terminating resistor in a possible configuration for an MPI network.
RS 485 repeater À
À
À
À Terminating resistor switched on
S7-400 S7-400
S7-400
Spur line
S7-300 À
OP OP
Programming device
Programming device
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Example of an MPI Network
* Only connected via spur line for startup/maintenance (with default MPI address)
** Connected to the MPI network later on (with default MPI address) 0 to x MPI addresses of nodes
À Terminating resistor switched on
S7-400** S7-400 S7-400 S7-400
S7-400 S7-400
0
11 10 9 8 7
1
2 3 4 5 6
OP OP
OP**
À À
S7-300
Programming device
Programming device*
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Example of a PROFIBUS-DP Network
* Only connected via spur line for startup/maintenance (with default PROFIBUS-DP address = 0) 0 to x PROFIBUS-DP addresses of nodes
S7-400 with CPU 414-2-DP
as DP Master ET 200M
0 8 7 6
1 2 3 4 5
Programming device* OP
ET 200M S5-95U
ET 200B ET 200B
À
À Terminating resistor switched on À
Programming device
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Example Using a CPU 414-2
The figure below shows an example of a configuration with CPU 414-2 DP which is integrated in an MPI network and simultaneously used as DP master in a
PROFIBUS-DP network.
In both networks, the node numbers can be assigned separately without conflicts resulting.
À Terminating resistor switched on
* Only connected via spur line for startup/maintenance MPI network
OP S7-400
S7-400 with CPU 414-2 as
DP master ET 200M
ET 200B
Programming Device Access Beyond Network Limits (Routing)
You can access all modules beyond network limits using a programming device.
PROFIBUS-DP network 2 MPI network 1
S7-400 with CPU 417
ET 200 S7-400 with
CPU 416
Programming device / PC 1
S7-300 with CPU 318
Programming device / PC 2 Programming device / PC 3
S7-300 with CPU 318 MPI network 3
Requirements
Use STEP 7 from version 5.0 onwards
Assign STEP 7 to a programming device or PC on the network (SIMATIC Manager, Assign programming device/PC)
The network limits are bridged by modules with routing capability.
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