Siemens SIMATIC S7-400H Manual page 90

Communications
Redundant connections:
CPU a1 –> CPU b1, CPU a2 –> CPU b2, CPU a1 –> CPU b2, CPU a2 –> CPU b1
Figure 7-2
Should the active partial connection fail, a previously established second partial
connection assumes responsibility for communications.
7-4
CPU a1
CP a1 Bus 1
CPU a2
CP a2
Fault-tolerant
system a
CP
CPU
a1 a1
CPU a1
CP a1
CP a2
CPU a2
Fault-tolerant Fault-tolerant
system a system b
CP
CPU CPU
a1
a1 b1
OLM OLM
Example of the Number of Resulting Partial Connections Being Dependent on
the Configuration
S7-400H Programmable Controller Fault-Tolerant Systems
Redundant connections
CPU b1
CP b1
Bus 2
CP b2 CPU b2
Fault-tolerant
system b
CPU CP
b1 b1
CP b1
LAN (red.)
CP b2
CP
b1
OLM
OLM
System bus as optical
two-fiber ring
Bus1
Bus2
CPU b1
CPU b2
A5E00068197-04