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

Communication
11.5 Communications via fault-tolerant S7 connections
11.5.2

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

Availability
Availability can be enhanced by using a redundant system bus and by using a fault-tolerant
CPU on a standard system.
If the communication partner is a fault-tolerant CPU, redundant connections can also be
configured, in contrast to systems with a 416 CPU for example.
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 11-6
Reaction to failure
Double errors in the fault-tolerant system (in other words, 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.
166
Example of redundancy with fault-tolerant system and fault-tolerant CPU
System Manual, 09/2007, A5E00267695-03
S7-400H