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  • Have you heard the word "Multiplex"? Commented Apr 23, 2017 at 16:03
  • like in tronixstuff.com/2011/08/26/… with the mentioned MCP23017 expander? Yes, I did. I am also aware about resistor dividers to read more buttons. But the question goes other way - can STM32 do it without such tricks? If so, I will start learning it today, if not, I will postpone it to next month or two. Commented Apr 23, 2017 at 16:13
  • playground.arduino.cc/Main/KeypadTutorial Commented Apr 23, 2017 at 16:14
  • Nice, but I am not going to use this device, and I want to be able read all combination of buttons. Also I would like to be able to use interrupts to detect change, which is not possible with scanning methods. Commented Apr 23, 2017 at 16:28
  • 2
    @gilhad Why it shouldn't be possible? You can set all columns to zero and enable pin change interrupts on all rows. And when the interrupt is detected, you can start scanning for a while (with pin change interrupts disabled). Or it can be used for waking up from the sleep mode. Commented Apr 23, 2017 at 16:38