Siemens SIMATIC S7 400

All CPUs have a plastic housing in which the control and display elements are integrated identically for all CPUs. Identical elements have identical functions.

On the front, there are:

• LEDs:
  For status and error indication.
• Toggle switches:
  For selecting the operating modes.
• Slot for a memory card (expansion of the load memory).
• Combined MPI/DP interface.
• Integrated PROFIBUS DP interface (not CPU 412-1).
• Battery infeed socket:
  For external supply of the battery backup voltage.

All CPUs apart from the entry level CPU 412-1 and CPU 412-2 PN have:

• PROFIBUS DP interface:
  For interfacing to distributed I/O. Depending on the configuration, it can even be used for communication with an OP or programming device/PC.

In addition, the CPU 412-2 PN, CPU 414-3 PN/DP, CPU 414F-3 PN/DP, CPU 416-3 PN/DP and the CPU 416F-3 PN/DP offer PROFINET connection options. Each of these modules has a PROFINET interface with 2 ports (switch).

The top-end CPUs also have:

• Spare slots for PROFIBUS DP interface modules:
  For connecting further DP lines.

Otherwise the CPUs only differ with regard to their quantity structure, e.g. RAM, address range, number of loadable blocks, and execution time.

Function

Memory concept

All CPUs of S7-400 feature two types of memory. This subdivision of work memory increases performance by 100%. Where a standard processor accesses its RAM at least twice, the S7-400 special processor accesses the code memory and data memory simultaneously in one cycle. There are also separate code and data buses for this purpose. The size of the work memory is determined by the appropriate CPU selected from the finely graded CPU spectrum.

For small and medium programs, the integral load memory (RAM) is sufficient. For larger programs, the load memory can be increased by inserting memory cards. Plug-in flash memory cards are available for retentive storage without the need for a battery.

Block encryption

The functions (FCs) and function blocks (FBs) can be stored in the CPU in encrypted form to protect the know-how of the application.