Siemens Automation System S7-400 - Manual (Page 103)

Networking
5-5
Automation System S7-400 Hardware and Installation
A5E00850741-01
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
station
One connection
resource occupied
One connection
resource occupied
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.