Connecting Redundant I/O; Redundant I/O In Central- And Expansion Devices - Siemens SIMATIC S7-400H Manual

Using I/O on the S7-400H
7.4

Connecting Redundant I/O

Was is redundant I/O?
I/O modules are considered redundant when there are two of each and are
configured and operated as redundant pairs. The use of redundant I/O provides
the highest degree of availability since it means that failure of a CPU failure and
failure of a signal module are both tolerated.
Configurations
The following configurations with redundant I/O are possible:
1. Redundant signal modules in the central and expansion devices
The signal modules are installed in pairs in the subsystems of CPU 0 and
CPU 1.
expansion unit
Figure 7-3
7-10
Redundant module pair
Central controller

Redundant I/O in central- and expansion devices

Central controller
expansion unit
Redundant module pair
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07