I guess, that sooner or later any developer has a question in his head – how do I save the data if the supply shut down?

There are some solutions listed:

• The reserve battery (the RTC clock, the motherboard);
• The constant saving to the memory – not nice, the EEPROM has limited cycles;
• Saving to the external memory – the complication of the PCB and the code;
• Saving when the lowering of the vdd level is detected – that what I need!