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1  Using Arduino / Microcontrollers / Re: Arduino Nano - A6/A7 internal pull-up resistors on: September 17, 2012, 10:04:47 am
Thanks for the explanation. Makes sense, just wasn't so obvious for a newbie like me :-)

Regarding pinMode(), that's curious. You mean it has no effect on A6/A7 because of their analog, input-only nature?

Because the page actually uses pinMode() on an analog pin. Ok, that's obviously to set it as OUTPUT. INPUT should be redundant, since they are input by default. But I thought it was a good measure to set them to INPUT, just in case some code previously had set them in OUTPUT mode...

2  Using Arduino / Microcontrollers / Arduino Nano - A6/A7 internal pull-up resistors on: September 17, 2012, 08:07:58 am

this is not mentioned anywhere in the documentation as far as I can see.

The question is: do the 2 extra analog pins (A6 and A7), which are found on the Arduino Nano and similar boards, have internal pull-ups?

I had a look at the ATmega datasheet, and it makes no mention of pull-ups for the two corresponding pins (ADC6 and ADC7, cfr. paragraph 1.1.9). It explicitly says, however, regarding the other pins (cfr. paragraphs 1.1.3, 1.1.4, 1.1.6) that they are "bi-directional I/O port with internal pull-up resistors".

So my guess is that there are no internal pull-up resistors for ADC6 and ADC7. Google also reports this explicitly mentioned on some AVR forum (

Is this true? Otherwise I must conclude that my board is faulty :-)

If this is the case, BTW, it would be nice to add this information on the Arduino Nano page, in order to spare some possible headache to other hobbists...

Some background and context: I'm using the analog pins to read an array of buttons, similar to what described here:,20125.0.html.

To keep the circuitry at a minimum, I turn on the internal pull-up by using:

  pinMode(A6, INPUT);
  digitalWrite(A6, HIGH);

The trick worked so far with A0 and A5, but it doesn't with A6. I'm getting wildly fluctuating readings with no buttons pressed, which suggests the internal pull-up is either broken or... simply non-existant :-)


3  Community / Website and Forum / Bug in Tone2 example on: April 26, 2012, 01:39:47 pm
ok, technically not a bug, but a documentation flaw. the comment in the code says:

 * 8-ohm speaker on digital pin 8

this should really be digital pin 9. not a big deal, but may be confusing if you're only looking at the code sample.

4  Community / Website and Forum / Minor fix to Examples > Basic > Blink on: March 16, 2012, 10:22:09 am

I noticed a small typo in the page

where it says:

"check out the DigitalReadSerial example to learn how read a switch connected to the Arduino"

there is a missing "to" in "learn how to read".

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