Note On S7400 Cpu: Connection Resources - Siemens S7-300 Configuration Manual

Characteristics of the Ethernet CPs
2.4 Slot rules for SIMATIC S7400
2.4.5

Note on S7400 CPU: Connection resources

Note that in the S7400 CPU, one S7 connection is reserved for a PG and a further one for an
OP (HMI = Human Machine Interface).
● Attaching the PG over MPI:
To run ONLINE functions from a PG (for example module diagnostics) on for, example an
S7400 CP, via the MPI interface, two connection resources (addressing of the interface
and the K bus) are required on the S7400 CPU. These two connection resources should
be taken into account in the number of S7 connections.
Example: The CPU 4121 has 16 free resources for S7 functions available. If a PG is to be
used for diagnostics on the S7400 CP and is connected to the MPI interface, two
connection resources are required on the S7400 CPU, so that 14 connection resources
remain available.
● PG connection via PROFIBUS or Industrial Ethernet
If the PG is connected to the LAN (PROFIBUS or Industrial Ethernet), to execute PG
functions on the S7400 CPU and diagnostics on an S7400 CP, only one connection
resource on the S7400 CPU is necessary.
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Configuring and commissioning S7 CPs for Industrial Ethernet
Configuration Manual, 09/2013, C79000-G8976-C182-13