Configuring Hardware and Communication Connections STEP 7.pdf

Configuring Central Racks
2.3.8 Assigning Addresses
There is a difference between assigning addresses to nodes and assigning
input/output addresses (I/O addresses).
Node addresses are addresses of programmable modules (MPI, PROFIBUS,
Industrial Ethernet addresses); they are required in order to be able to address the
various nodes in a subnet, for example, in order to download a user program to a
CPU. You will find information on assigning node addresses in the subnet in the
chapter on networking stations.
Input/output (I/O) addresses are required in order to read inputs and set outputs in
the user program.
Special Feature: MPI Addresses of FMs and CPs (S7-300)
Communications processors (CPs) and function modules (FMs) with their own MPI
address have a special feature: their MPI address is determined automatically by
the CPU and assigned according to the following pattern:
• First CP/FM after the CPU: MPI address of the CPU + 1
• Second CP/FM after the CPU: MPI address of the CPU + 2
The newer S7-300 CPUs (see CPU manual or Product Information) permit free
MPI address allocation for such CPs and FMs (via the "General" tab for the
module).
Configuring Hardware and Communication Connections with STEP 7
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