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Having my Arduino Nano 328P disconnected from any circuitry and setting all pins to pinMode(OUTPUT) and writing LOW to (almost) all the pins, when I connect my multimeter to every output pin and the Arduino ground, I measure 0.7 volts on pin 2 and 0.0 volts on 3 to 19. Here I mean the pin numbers on the edge of the Nano, not the processor pins.

For my project it worked out fine because I needed those 0.0 and not the 0.7, but I'm afraid it suddenly might not be pin 2 that's 0.7 in the future and my circuit would fail.

Why is there this one pin giving 0.7 instead of 0.0 and how can I make sure or argue that it will only be pin 2 that gives 0.7?

EDIT as per request, the full test code is below.

void setup() {
  for (int i=1;i<20;i++){
  pinMode(i, OUTPUT);
  }
}

void loop() {
  for (int i=1;i<20;i++){
    digitalWrite(i, HIGH);  
  }
    delay(3000);               
    for (int i=1;i<20;i++){
    digitalWrite(i, LOW);   
    }
    delay(3000);               
}
  • What voltage is your 328P running at? At 5V, 0.7V is still perfectly within specification (0.9V max V[OL]). – Majenko Oct 2 '16 at 11:38
  • @Majenko I'm not sure exactly, I'm running it via a phone wall adapter which outputs 5V/1A which I think should be enough, how could I check if it really is? If you think it's the voltage provided, I'll check when powering it via my laptop. – PHPirate Oct 2 '16 at 12:27
  • No, you misunderstand. There are two options for running the boards like the Micro / Nano, etc - 5V or 3.3V. The V[OL] specification changes depending on supply voltage, and that is fixed by the board, not the PSU. It sounds like you have a 5V version anyway, so the output is within specification. – Majenko Oct 2 '16 at 12:29
  • 1
    @Majenko To summarize 660 pages into 444 seems weird to me, haha. atmel.com/Images/… – PHPirate Oct 2 '16 at 12:57
  • 1
    @Majenko I think you should post your comments as one answer. – jfpoilpret Oct 2 '16 at 13:23
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For future reference, thanks to Majenko: these values fall within the expected voltage output range of 0-0.9V, and you cannot be certain it will stay this way. See the datasheet page 313.

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