Siemens SIMATIC S7-400H Manual page 174

Communication Functions
Redundant connections:
CPU a1 –> CPU b1, CPU a2 –> CPU b2, CPU a1 –> CPU b2, CPU a2 –> CPU b1
Figure 8-2
Should the active partial connection fail, a previously established second partial
connection assumes responsibility for communications.
8-4
CPU a1 CP a1
CPU a2
CP a2
Fault-tolerant
system a
CPU CP
a1 a1
CPU a1
CP a1
CP a2
CPU a2
Fault-tolerant system a Fault-tolerant system b
CP
CPU CPU
a1
a1 b1
OLM
OLM
Example of the number of resulting partial connections being dependent on
the configuration
Redundant connections
CP b1
Bus 1
Bus 2
CP b2
Fault-tolerant
system b
CP
CPU
b1
b1
CP b1
LAN (red.)
CP b2
CP
b1
OLM
OLM
System bus as optical two-fiber ring
Automation System S7-400H Fault-tolerant Systems
CPU b1
CPU b2
Bus 1
Bus 2
CPU b1
CPU b2
A5E00068197-07