Connection (S7 Connection); Fault-Tolerant S7 Connections; Example Of An S7 Connection - Siemens SIMATIC S7-400H Manual

Connection (S7 Connection)

A connection is the logical assignment of two communication peers to implement a
communication service. Every connection has two endpoints containing the
information required for addressing the communication peer and other attributes
for establishing the connection.
An S7 connection is the communication connection between two standard CPUs or
from one standard CPU to a CPU in a fault-tolerant system.
In contrast to a fault-tolerant S7 connection, which contains at least two partial
connections, an S7 connection actually consists of just one connection
Communications are terminated should this one connection fail.
Figure 8-1
Note
Generally speaking, "connection" in this manual means the "configured S7
connection". For other types of connection please refer to the manuals SIMATIC
NET NCM S7 for PROFIBUS and SIMATIC NET NCM S7 for Industrial Ethernet.

Fault-tolerant S7 connections

The requirement for higher availability by means of communication components –
for example, CPs and buses – necessitates redundant communication connections
between the systems involved.
Unlike the S7 connection, a fault-tolerant S7 connection consists of at least two
lower-level partial connections. From the point of view of the user program, the
configuration and the connection diagnostics, the fault-tolerant S7 connection with
its subordinate partial connections is represented by exactly one ID (like a
standard S7 connection). Depending on the configuration set, it can consist of up
to four partial connections, of which two are always made (active) so as to
maintain communications in the event of an error. The number of partial
connections depends on possible alternative paths (refer to Figure 8-2) and is
determined automatically.
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
CPU 0
CPU
CPU 1

Example of an S7 connection

Communication Functions
S7 connection
8-3