Communication Between Fault-Tolerant Systems - Siemens SIMATIC CPU 410 System Manual

Supplementary information
18.11 Communication via fault-tolerant S7 connections
You program the fault-tolerant communication with STEP 7 using communication SFBs.
These communication blocks can be used to transmit data over subnets (Industrial Ethernet,
PROFIBUS). The communication SFBs integrated in the operating system enable an
acknowledged data transmission. In addition to data transfer, you can also use other
communication functions for controlling and monitoring the communication peer.
User programs written for S7 connections can also be used for fault-tolerant S7 connections
without program modification. Cable and connection redundancy has no effect on the user
program.
Note
For information on programming the communication, refer to the STEP 7 documentation
(e.g.,
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 Reference Manual
S7-300/400, System and Standard Functions
Disruptions of a subconnection while communication jobs are active over fault-tolerant S7
connections can extend the runtime of these jobs.
Note
Downloading the connection configuration during operation
If you download a connection configuration during operation, established connections may
be terminated.
18.11.1

Communication between fault-tolerant systems

Availability
The easiest way to increase the availability between linked systems is to use a redundant
plant bus. This is set up with a duplex fiber-optic ring or a dual electrical bus system. The
connected nodes may consist of simple standard components.
Availability can best be enhanced using a duplex fiber-optic ring. If a break of the two-fiber
fiber-optic cable occurs, communication is maintained between the systems involved. The
systems then communicate as if they were connected to a bus system (line). A ring topology
basically contains two redundant components and automatically forms a 1-out-of-2
redundancy node. The fiber-optic network can also be set up in star topology as redundant
bus.
If one electrical cable segment fails, communication between the participating systems is
also upheld (1-out-of-2 redundancy).
The following examples illustrate the differences between a duplex fiber-optic ring and a dual
electrical bus system.
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Programming with STEP 7
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CPU 410 Process Automation/CPU 410 SMART
System Software for
System Manual, 05/2017, A5E31622160-AC