Communication Functions
8-18
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
8.5.2 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 8-11 shows an example of such a configuration.
Fault-tolerant system a Standard system b
Bus 1
Bus 2
CPU
a1
CP
a1
CPU
b1
CP
b2
CPUb1
CPUa2
CPUa1
CPa1
CPa2
CPb1
Bus 1
Bus 2
Redundancy
block diagram
Fault-tolerant
system a
Standard system
CP
b1
CPb2
Figure 8-11 Example of redundancy with fault-tolerant systems and redundant bus system
with redundant standard connections
Response to failure
Double faults in the fault-tolerant system (in other words, CPUa1 and CPa 2),
double faults in the standard system (CPb1 and CPb2) and a single fault in the
standard system (CPb1) result in a complete failure of communication between the
systems involved (refer to Figure 8-11).
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