S7 Communication - Siemens SIMATIC S7-1500 Function Manual

S7 communication

Characteristics of S7 communication
S7 communication as homogeneous SIMATIC communication is characterized by vendor-
specific communication between SIMATIC CPUs (not an open standard). S7 communication
is used for migration and for connecting to existing systems (S7-300, S7-400).
For data transfer between two S7-1500 automation systems, we recommend that you use
open communication (see section Open User Communication (Page 65)).
Properties of S7 communication
Using S7 communication, the CPU exchanges data with another CPU. Once the user has
received the data at the receiver end, the reception data is automatically acknowledged to
the sending CPU.
The data is exchanged via configured S7 connections. S7 connections can be configured at
one end or at both ends.
S7 communication is possible via:
● Integrated PROFINET or PROFIBUS DP interface of a CPU
● Interface of a CP/CM
S7 connections configured at one end
For an S7 connection configured at one end, the configuration for this connection takes
place in only one communication partner and is only downloaded to it.
A one-sided S7 connection can be configured to a CPU that is only a server of an S7
connection (e.g. CPU 315-2 DP). The CPU is configured and the address parameters and
interfaces are thus known.
In addition, a one-sided S7 connection can be configured to a partner who is not in the
project and whose address parameters and interface and therefore are not known. You need
to enter the address; it is not checked by STEP 7. The partner is initially unspecified (no
partner address is registered when you create the S7 connection). Once you enter the
address, it is "unknown" (i.e. it is named, but the project is unknown).
This makes it possible to use S7 connections beyond the boundaries of a project. The
communication partner is unknown to the local project (unspecified) and is configured in
another STEP 7 or third-party project.
S7 connections configured at both ends
When an S7 connection is configured at both ends, the configuration and download of the
configured S7 connection parameters takes place in both communication partners.
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Communication