Communication Between Fault-Tolerant Systems And A Fault-Tolerant Cpu - Siemens SIMATIC S7-400H System Manual

Communication
14.6 Communication via fault-tolerant S7 connections
14.6.2

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 14-17 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 a
standard system (CPUb1) lead to a total failure of communication between the systems
involved; see previous figure.
250
System Manual, 03/2012, A5E00267695-11
S7-400H