Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 - Manual (Page 57)

Communication
3.3 S7 connections
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05
3-29
3.3.3 Distribution and availability of S7 connection resources
Distribution of connection resources
Table 3-10 Distribution of connections
Communication service Distribution
PG communication
OP communication
S7 basic communication In order to avoid allocation of connection resources being dependent only on
the chronological sequence in which various communication services are
requested, connection resources can be reserved for these services.
For PG and OP communication respectively, at least one connection
resource is reserved by default.
In the table below, and in the technical data of the CPUs, you can find the
configurable S7 connection resources and the default configuration for each
CPU. You "redistribute“ connection resources by setting the relevant CPU
parameters in STEP 7.
S7 communication
Other communication resources (e.g. via
CP 343-1, with a data length of
> 240 bytes)
Here you allocate connection resources which are still available and not
reserved for a specific service (PG/OP communication, S7-based
communication).
Routing PG functions
(only for CPUs with DP/PN interface) The CPUs provide a certain number of connection resources for routing.
These connections are available in addition to the connection resources.
The subsection below shows the number of connection resources.
Global data communication
Point-to-point communication These communication services do not use connection resources.
Open communication by means of TCP/IP This communication service does not occupy any connection resources.
Eight connections are available in parallel.
SNMP This communication service does not occupy any connection resources.