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.
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).
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.