Communications Over Redundant S7 Connections - Siemens SIMATIC S7-400H Manual

7.5.2

Communications over Redundant S7 Connections

Availability
Availability can be enhanced by using a redundant system bus and by using two
separate CPs on a standard system.
Redundant communications can be operated even with standard connections. Two
separate S7 connections have to be configured for this. Connection redundancy
has to be implemented by means of programming for this purpose. Communication
monitoring has to be implemented for both connections at the user program level
to detect a communications failure and to switch to the second connection.
Figure 7-9 shows an example of such a configuration.
Redundancy
block diagram
Figure 7-9
Failure behavior
Double errors on the fault-tolerant system – in other words, CPUa1 and CPa 2 –
double errors on the standard system (CPb1 and CPb2) and a single error on the
standard system (CPUb1) result in total failure of communications between the
systems involved (refer to Figure 7-9).
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Fault-tolerant
system a
CPU CP
a1 a1
Fault-tolerant system a
CPUa1
CPa1
CPUa2 CPa2
Example of Redundancy with Fault-Tolerant Systems and Redundant Bus
System with Redundant Standard Connections
Standard system b
CPU CP CP
b1 b1 b2
Standard system
CPb1
Bus1
CPUb1
CPb2
Bus2
Communications
Bus1
Bus2
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