Communications Between Fault-Tolerant Systems And A; Fault-Tolerant Cpu - Siemens SIMATIC S7-400H Manual

7.4.2

Communications 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 peer is a CPU 417-4 H, fault-tolerant connections can be
configured again here, as opposed to a CPU 416, for example.
Note
Fault-tolerant connections occupy two connection resources on CP b1 for the
redundant connections. One connection resource each is assigned to CP a1 and
CP a2.
Redundancy
block diagram
Figure 7-5
Failure behavior
Double errors in the fault-tolerant system (i.e. CPUa1 and CPa2) and single errors
in the standard system (CPUb1) result in a total failure of communications between
the redundant systems involved (refer to Figure 7-5).
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Fault-tolerant system a
CPU CP
a1 a1
OLM OLM
Fault-tolerant system a
CPUa1 CPa1
CPUa2 CPa2
Example of Redundancy with Fault-Tolerant System and CPU 417-4H
Standard system with CPU 417-4H
CPU CP
b1 b1
OLM
Standard system with CPU 417-4H
Bus1
CPUb1
CPb1
Bus2
Communications
System bus as opti-
cal two-fiber ring
7-11