SIMATIC S7-400 SERIES,SIEMENS S7-400 process controller


Part of the SIMATIC process controller series, the S7-400 has been designed for system solutions in the fields of manufacturing and process automation. This process controller is ideal for data-intensive tasks that are especially typical for the process industries. High processing speeds and deterministic response times ensure short machine cycle times on high-speed machines in the manufacturing industry.


S7-400 CPUs


S7-400 controller performance classes

There is a graded range of CPUs from the entry-level CPU right up to the high-performance CPU for configuring the controller. All CPUs control large quantity structures; several CPUs can work together in a multicomputing configuration to boost performance. Thanks to their high processing speed and deterministic response times, the CPUs enable short machine cycle times.

The different CPUs are distinguished by, for example, work memory, address range, number of connections and execution time. As well as the standard CPUs, there are also two failsafe and three fault-tolerant CPUs available.


  • The S7-400 is especially suitable for data-intensive tasks in the process industry. High processing speeds and deterministic response times guarantee short machine cycle times on high-speed machines in the manufacturing industry.
  • The S7-400 is used preferably to coordinate overall plants and to control lower-level systems. This is guaranteed by the high communication power and the integral interfaces.
  • Many of the S7-400 components are also available in a SIPLUS version for extreme environmental conditions.

S7-400 finds successful application here:

  • Automotive industry
  • Standard mechanical equipment manufacture incl. custom mechanical equipment manufacture
  • Warehousing systems
  • Building engineering
  • Steel industry
  • Power generation and distribution
  • Paper and printing industries
  • Woodworking
  • Textile manufacture
  • Pharmaceuticals
  • Food and beverages industries
  • Process engineering, e.g. water and wastewater utilities
  • Chemical industry and petrochemicals

  • The power of the S7-400 is scalable thanks to a graded range of CPUs; the capacity for I/O is almost unlimited.
  • The power reserves of the CPUs enable new functions to be integrated without further hardware investment, e.g. processing of quality data, user-friendly diagnosis, integration into higher-level MES solutions or high-speed communication via bus systems.
  • The S7-400 can be structured in a modular way; there is a widely varied range of modules available both for centralized configurations and distributed structures. This results in very cost-effective spare parts handling.
  • The configuration of the distributed I/O of the S7-400 can be modified during operation (Configuration in Run). In addition signal modules can be removed and inserted while live (hot swapping). This makes it very easy to expand the system or replace modules in the event of a fault.
  • The storage of the complete project data including symbols and comments on the CPU simplifies service and maintenance calls.
  • Safety engineering and standard automation can be integrated into a single S7-400 controller; plant availability can be increased through the redundant structure of the S7-400.
  • Many of the S7-400 components are also available in a SIPLUS version for external environmental conditions, e.g. extended temperature range (-25?+60°C) and for use where there is aggressive atmosphere/condensation.
  • The high-speed backplane bus of S7-400 ensures efficient linking of central I/O modules
Design and function


An important feature of the S7-400 is its modularity. The powerful backplane bus of the S7-400 and the DP communication interfaces that can be plugged directly onto the CPU allow the high-performance operation of many communication lines. This permits, for example, the division into one communications line for HMI and programming tasks, one line for high-performance and equidistant motion control components, and one “normal” I/O fieldbus.
Additionally required connections to MES-/ERP systems or the Internet via SIMATIC IT can also be implemented. The S7-400 can be expanded centrally or in a distributed configuration depending on the task. Add-on devices and interface modules are available centrally for this purpose. Distributed expansion is possible over the PROFIBUS or PROFINET interfaces integrated in the CPUs. If required, communication processors (CPs) can also be used.


An S7-400 system basically comprises a rack, power supply, and central processing unit. It can be installed and expanded in a modular way. All modules can be positioned freely next to the power supply plugged in on the left. The S7-400 has a rugged design without a fan. Signal modules can be hotswapped.A multi-faceted module range can be used for central expansions as well as for simple configuration of distributed topologies with ET 200.
In a centralized expansion, additional mounting racks are connecteddirect to the central controller.

In addition to the standard mounting racks, aluminum mounting racks with 9 and 18 slots are also available. These aluminum racks are highly resistant to unfavorable environmental conditions, and they are more rigid and around 25% lighter.


Multicomputing, that is, the simultaneous operation of several CPUs in one S7-400 central controller, offers users different benefits:

  • The overall performance of an S7-400 can be shared by means of multicomputing. For example, complex tasks in technologies such as open-loop control, computing or communication can be split and assigned to different CPUs. Each CPU is assigned its own, local I/O for this purpose.
  • Some tasks can also be disconnected from each other in multicomputing, that is, one CPU processes the time-critical process tasks and another handles the non-time-critical tasks.

In multicomputing operation, all CPUs behave like a single CPU, that is, when one CPU goes to STOP, the others are also halted. The actions of several CPUs can be coordinated selectively by instruction via synchronization calls.In addition, data exchange between the CPUs takes place at an extremely high speed via the “global data” mechanism.

Data/program memory

The size of the work memory is determined CPU that can be selected from a finely graded range of CPUs.The integral load memory (RAM) is sufficient for small to mediumsized programs. For larger programs, the load memory is enlarged by plugging in RAM or FEPROM memory cards (64 KB to 64 MB).

Special functions

The S7-400 CPUs have some highly useful special functions:

  • Simpler and faster upgrade due to firmware update via network from an engineering workstation
  • Additional write-protection (for e.g. no component download from PC to CPU) via a system function
  • Optional know-how protection by reading the serial number of the memory card, so that it is ensured that the program runs only with the particular memory card

An integrated data record gateway permits integrated accessto data records across different bus systems and networkboundaries e.g. a control-level PC can communicate via PROFINETwith a lower-level S7-400 controller and the field devicesconnected to it via PROFIBUS.

S7-400 Communication processors


Communication processors are used for connecting S7-400 to the different bussystems / communication networks as well for point-to- point link.

Point-to-point connection
Point-to-point link via communications processors (CPs) is an extremely powerful and low-cost alternative to bus systems. The advantage of point-to-point links over bus systems is especially pronounced when only a few (RS 485) devices are to be connected to the SIMATIC S7.
The CPs can also easily link third-party systems to the SIMATIC S7. Thanks to the great flexibility of the CPs, different physical transmission media, transmission rates or even customized transmission protocols can be implemented. For each CP, there is a configuring package on CD with electronic manual, parameterization screen forms and standard function blocks for communication between the CPU and the CP. The configuration data are stored in a system block and backed up in the CPU. When modules are replaced, the new module is therefore immediately ready for use.
With the S7-400 point-to-point link modules, adaptation to the physical transmission media is achieved by plugging in the relevant interface submodules, without the need for external converters.


Communication modules allow connection of the SIMATIC S7-400 for instance to:

  • SIMATIC S7 and SIMATIC S5 programmable controllers, and systems from many other manufacturers
  • PCs, programming devices, hmi devices
  • Field devices
  • Scanners, bar code readers
  • Measuring systems
  • Scales, etc.


• Reduced start-up times due to the easy configuration with STEP 7
• Reduced downtimes and service times in the event of a fault through LED displays

Design and function

The CPs have a rugged plastic housing with LEDs for displaying operating states and faults. They show all advantages of the SIMATIC S7-300- Design, e.g.
• Compact design
• Easy installation
• User friendly wiring, etc.

S7-400 Function modules


The multi-facetted module range of S7-400 allows modular customization to suit the most varied tasks.
Apart from the CPUs with integrated functions and interfaces, there is a wide range of special modules in S7-400 design for technology.

Range of application

  • Wood, glass, stone and metal processing
  • Packaging machines
  • Presses
  • General machine manufacturing
  • Machine tools
  • Textile machines
  • Rubber and plastic industry
  • Plants


  • High degree of accuracy and dynamic response
  • Specialized and universal modules with a wide range of functions
  • CPU is not involved since the functionality is stored in the firmware of each module
  • Quick reaction times (deterministic dynamic response)
  • Engineering with configuring tool, integrated into STEP 7

Design and function

Function modules are intelligent modules that independently execute the technological tasks and thus reduce the load on the CPU. They are used when a high level of accuracy and dynamic response is required.


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