Siemens SIMATIC S7-300 Series Reference Manual page 147

Connection resources
CPU 318-2 provides a total of 32
communication resources, that is, 32 of
those via MPI/DP interface or 16 via DP
interface.
Those connection resources are freely
available for
S
PD/OP communication
S
S7 basic communication
S
S7 communication and
S
Routing of PD communication
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
CPU Function, depending on CPU and STEP 7 Version
CPU 318-2 CPUs 312IFM to 316-2DP
The CPUs provide a specific number of
connection resources.
For
S
PD communication
S
OP communication and
S
S7 basic communication
you can reserve connection resources
which can then not be used by any other
communication function.
The remaining connection resources are
then available for PD/OP/S7 basic and S7
communication.
For routing, the CPUs 315-/316-2 provide
additional connection resources for 4
routing connections.
4-5