Siemens SIMATIC S7-400H - Other possibilities for connecting redundant I;O

Using I/O on the S7-400H
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Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
7.5 Other possibilities for connecting redundant I/O
Redundant I/O on the user level
If you cannot use the redundant I/O (Chapter 7.4) supported by the system
(perhaps because the redundancy module is not included in the list of supported
modules), you may be able to use redundant I/O on the user level.
Configurations
The following configurations having a redundant I/O are possible (Figure 7-13):
1. Redundant system with one-way central and/or distributed I/O.
One I/O module is inserted for this purpose in the subsystems of CPU 0 and
one in the subsystem of CPU 1.
2. Redundant configuration with a switched I/O
Two I/O modules are inserted into two ET 200M distributed I/O devices with an
active backplane bus.
Redundant one-way I/O
Redundant switched I/O
Figure 7-13 Redundant one-way and switched I/Os