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Arduino device unused I/O's...... what to do with them?

colporteur

What is the best practice for unused Arduino device I/O pins, connect them to ground or Vcc? If not connected on the PCB what if anything do you do with them in code?

My go to bathroom reading material is The Art of Electronics Paul Horowitz & Winfield Hill. I just read a section on routine design considerations. "No open inputs" is the suggestion. It was a discussion on CMOS design but the commentary got me to thinking about Arduino's. 

I've never done anything with them. I assumed they were conditioned in the device.

For No Open Inputs planning, I wonder how the pro's in E14 handle it.

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  • With a microcontroller, I program all unused pins as inputs (analog input is also possible, but this can interfere with the ADC) and terminate them either to ground (a hard connection to ground is usually possible, depending on the manufacturer; otherwise, a soft connection to ground is used) -> or to a pull-down resistor (around 1kΩ; this can sometimes introduce noise).
    The datasheet usually provides the relevant information.

    If the software doesn't address the pin, then it's generally not reacting to disturbances occurring on the "open" or terminated pin.
    Also, here you can let open the pin, depending to the manufacturer.

    Unless these are over voltages or, CAUTION - !!!!! negative voltages (<< -0.3V).

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  • With a microcontroller, I program all unused pins as inputs (analog input is also possible, but this can interfere with the ADC) and terminate them either to ground (a hard connection to ground is usually possible, depending on the manufacturer; otherwise, a soft connection to ground is used) -> or to a pull-down resistor (around 1kΩ; this can sometimes introduce noise).
    The datasheet usually provides the relevant information.

    If the software doesn't address the pin, then it's generally not reacting to disturbances occurring on the "open" or terminated pin.
    Also, here you can let open the pin, depending to the manufacturer.

    Unless these are over voltages or, CAUTION - !!!!! negative voltages (<< -0.3V).

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