Siemens S7-400 Rules for MPI Addresses, PG / OP -- Module communication without MPI

Networking

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.

PG or OP

CPU

MPI

CP or FM

C bus

S7-400 station

One connection	Two connection resources	One connection
resource occupied	occupied in the CPU	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.

Automation System S7-400	Hardware and Installation	5-5
A5E00850741-01