Communication Between Fault-Tolerant Systems And A Fault-Tolerant Cpu - Siemens SIMATIC PCS 7 System Manual

Supplementary information
16.10 Communication via fault-tolerant S7 connections
Fault-tolerant S7 connections
Any disruption of subconnections while communication jobs are active over fault-tolerant S7
connections leads to extended delay times.
16.10.2

Communication between fault-tolerant systems and a fault-tolerant CPU

Availability
Availability can be enhanced by using a redundant plant bus and by using a fault-tolerant
CPU in a standard system.
If the communication peer is a fault-tolerant CPU, redundant connections can also be
configured, in contrast to systems with a standard CPU.
Note
Fault-tolerant connections use two connection resources on CP b1 for the redundant
connections. One connection resource each is occupied on CP a1 and CP a2 respectively.
In this case, the use of further CPs in the standard system only serves to increase the
resources.
Figure 16-19 Example of redundancy with fault-tolerant system and fault-tolerant CPU
Response to failure
Double errors in the fault-tolerant system, i.e., CPUa1 and CPa2, or single errors in the
standard system, i.e., CPUb1, lead to a total failure of communication between the systems
involved. This can be seen in the previous figure.
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System Manual, 09/2014, A5E32631667-AB