The SIMATIC S7-400H consists of the following components:

• 2 central controllers:
  Either 2 separate UR1/UR2 central controllers or 2 areas on one divided central controller (UR2-H).
• 2 sync modules per central controller for linking both devices via fiber optic cable.
• 1 CPU 412-5H, 1 CPU 414-5H, 1 CPU 416-5H or 1 CPU 417-5H per central controller.
• S7-400 I/O modules in the central controllers.
• UR1/UR2/ER1/ER2 expansion units and/or ET 200M distributed I/O devices with I/O modules.

Central functions are always redundant in design.

I/O can be configured with normal availability or switched.

Normally available I/O (one-sided configuration)

In a one-sided configuration, I/O modules are single-channel in design and are addressed by only one of the two central controllers. One-sided I/O modules can be plugged into

• a central controller and/or
• expansion units/distributed I/O devices

.

Information read in on one side is always available to both central controllers, provided the device addressing the I/O is working correctly. In the event of a fault, the I/O modules of the affected central controller are out of service.

One-sided configuration is used:

• For plant sections that do not require increased availability.
• for connecting a user-program-based, redundant I/O. The system has to be set up symmetrically here.

Increased availability (switched configuration)

In a switched configuration, I/O modules are single-channel in design but they are addressed via a redundant PROFIBUS DP by both central controllers. Switched I/O modules can only be plugged into

• ET 200M distributed I/O devices

.

Redundancy of the I/O

The redundancy of the I/O is supported in operating system version 3.1 or higher.

Redundant I/O modules are configured redundantly in pairs. The use of redundant I/O offers maximum availability because in this way, the failure of a CPU, a PROFIBUS or a signal module is tolerated.

The redundant I/O on the system side is only supported if it is connected via PROFIBUS DP. If I/O modules that are connected to PROFINET are to be operated, this is can done via the user program.

Configuration options

The following configurations are possible:

• Redundant I/O in single-sided DP slaves
• Redundant I/O in switched DP slaves

Suitable I/O modules

The mutually redundant modules must be of the same type and design (e.g. both centralized or both distributed). The slots are not stipulated. However, use in different stations is recommended for availability reasons. Please refer to Customer Support or the manual to see which modules can be used.

Redundancy of the FMs and CPs

Function modules (FMs) and communications processors (CPs) can be used redundantly in two different configurations:

• Switched redundant configuration:
  The FMs/CPs can be connected in duplicate to separate ET 200Ms or one switched ET 200M.
• Two-channel redundant configuration:
  FMs/CPs can be plugged into both subunits or into expansion units connected to the subunits (see one-sided configuration).

The redundancy of the modules is achieved in different ways here:

• Programming by the user:
  On the function modules and the SIMATIC CPs, the redundancy function can generally be programmed by the user.The active module is determined and a possible fault is detected to initiate a switchover. The required program corresponds to the program for a single CPU with redundant FM/CP:
• Direct support from the operating system.
  In the case of SIMATIC NET-CP 443-1, the operating system supports the redundancy direct. For further details, see under Communication.