Siemens SIMATIC C7-626 Installation, Assembly, Wiring page 53

Recommendation The MPI addresses set at the factory should not be assigned as fixed node
for MPI Addresses
addresses since, otherwise, address conflicts (double MPI addresses) can
in the Network
arise when devices are replaced or the network is expanded.
This avoids double assignment of MPI addresses after installing a further
preset C7 or S7-300 in the MPI network (for example, when replacing a C7).
Recommendation
Reserve the L2 address "0" for a service programming device which may be
for PROFIBUS
temporarily connected to the L2-DP network at a later stage if required. You
Addresses
should therefore assign other L2 addresses to the programming devices
included in the L2-DP network.
Components You connect the individual nodes via the bus connectors and the PROFIBUS
bus cable. Remember to provide for the nodes a bus connector with
programming device socket to which a programming device can be
connected if required (see also Section 3.5).
Use the RS 485 repeater for connections between segments or for extending
cables.
Using the RS 485
See the reference manual /71/ for details of how to install and use a repeater.
Repeater
Terminating
A cable must be terminated with a surge impedance. To do this, switch on the
Resistance
terminating resistance at the first and last node of the network.
At least one of these two nodes must be supplied with power.
Terminating
Figure 3-2 shows you where to connect the terminating resistance on the bus
Resistance On Bus connector.
Connector
Figure 3-2
C7-626 / C7-626 DP Control Systems
C79000-G7076-C626-01
Configuring MPI Networks and PROFIBUS-DP Networks
Reserve the MPI address "0" for a service programming device.
Reserve the address "1" for the C7 OP.
Reserve the address "2" for the C7 CPU.
Terminating
resistance
on
switched on
off
Terminating Resistance on the Bus Connector
Terminating
on
resistance
off
switched off
3
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