Communication with the S7-300
5.4 S7 communication structure
5.4 5.4 S7 communication structure
5.4.1 Communication path of an S7 connection
An S7 connection is established when S7 modules communicate with one another. This
connection is the communication path.
Note
Global data communication and point-to-point links do not require S7 connections.
Every communication link requires S7 connection resources on the CPU for the entire
duration of this connection.
Thus, every S7 CPU provides a specific number of S7 connection resources. These are
used by various communication services (PG/OP communication, S7 communication or S7
basic communication).
Connection points
An S7 connection between modules with communication capability is established between
connection points. The S7 connection always has two connection points: The active and
passive connection points:
• The active connection point is assigned to the module that establishes the S7 connection.
• The passive connection point is assigned to the module that accepts the S7 connection.
Any module that is capable of communication can thus act as an S7 connection point. At the
connection point, the established communication link always uses
one S7 connection of the
module concerned.
Transition point
If you use the routing functionality, the S7 connection between two modules capable of
communication is established across a number of subnets. These subnets are
interconnected via a network transition. The module that implements this network transition
is known as a router. The router is thus the point through which an S7 connection passes.
Any CPU with a DP interface can be the router for an S7 connection. You can establish a
certain maximum number of routing connections. This does not limit the data volume of the
S7 connections.
The number of routing connections can be found in the Technical Specifications.
S7-300 CPU Data: CPU 315T-2 DP
5-14 Manual, 12/2005, A5E00427933-02
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