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.