Communication Via S7 Connections; Communication Via S7 Connections - One-Sided Mode - Siemens SIMATIC S7-400H System Manual

11.6

Communication via S7 connections

Communication with standard systems
Fault-tolerant communication between fault-tolerant and standard systems is not supported.
The following examples illustrate the actual availability of the communicating systems.
Configuration
S7 connections are configure in STEP 7.
Programming
All communication functions are supported for standard communication on a fault-tolerant
system.
The communication SFBs are used in STEP 7 to program communication.
Note
The START and STOP communication functions act on exactly one CPU or on all CPUs of
the fault-tolerant system (for more details refer to the
System and Standard Functions
11.6.1

Communication via S7 connections - one-sided mode

Availability
Availability is likewise enhanced by using a redundant system bus for communications
between fault-tolerant and standard systems.
On a system bus configured as multimode fiber optic ring, communication between the
partner systems is maintained if the multimode fiber optic cable breaks. The systems then
communicate as if they were connected to a bus system (linear structure); see following
figure.
For linked fault-tolerant and standard systems, the availability of communication can not be
improved by means of a dual electrical bus system. To be able to use the second bus
system as a redundant system , you configure a second S7 connection and manage it
accordingly in the user program (see figure after next).
S7-400H
System Manual, 09/2007, A5E00267695-03
11.6 Communication via S7 connections
System Software for S7-300/400,
reference manual) reference manual.
Communication
169