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						<span id="top_subject" class="topic-icon topic-icon-">Topic: Arduino Nano - A6/A7 internal pull-up resistors&nbsp;<span>(Read 42291 times)</span></span>
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								<div id="subject_926196" class="subject_title"><a href="https://forum.arduino.cc/index.php?topic=123176.msg926196#msg926196" rel="nofollow">Arduino Nano - A6/A7 internal pull-up resistors</a></div>
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									<a href="https://forum.arduino.cc/index.php?topic=123176.msg926196#msg926196" rel="nofollow" title=" - Arduino Nano - A6/A7 internal pull-up resistors" class="smalltext">Sep 17, 2012, 03:07 pm</a>
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								<div class="inner" id="msg_926196">Hello,<br /><br />this is not mentioned anywhere in the documentation as far as I can see.<br /><br />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?<br /><br />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 &quot;bi-directional I/O port with internal pull-up resistors&quot;. <br /><br />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 (http://www.avrfreaks.net/index.php?name=PNphpBB2&amp;file=printview&amp;t=89804&amp;start=0).<br /><br />Is this true? Otherwise I must conclude that my board is faulty :-)<br /><br />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...<br /><br />Some background and context: I&#039;m using the analog pins to read an array of buttons, similar to what described here: http://arduino.cc/forum/index.php/topic,20125.0.html.<br /><br />To keep the circuitry at a minimum, I turn on the internal pull-up by using:<br /><br /><div class="codeheader">Code: <a href="javascript:void(0);" onclick="return smfSelectText(this);" class="codeoperation">[Select]</a></div><code class="bbc_code">&nbsp; pinMode(A6, INPUT);<br />&nbsp; digitalWrite(A6, HIGH);<br /></code><br /><br />The trick worked so far with A0 and A5, but it doesn&#039;t with A6. I&#039;m getting wildly fluctuating readings with no buttons pressed, which suggests the internal pull-up is either broken or... simply non-existant :-)<br /><br />cheers,<br />Aldo<br /><br /><br /><br /></div>
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								<div id="subject_926207" class="subject_title"><a href="https://forum.arduino.cc/index.php?topic=123176.msg926207#msg926207" rel="nofollow">Re: Arduino Nano - A6/A7 internal pull-up resistors</a></div>
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									<a href="https://forum.arduino.cc/index.php?topic=123176.msg926207#msg926207" rel="nofollow" title="Reply #1 - Re: Arduino Nano - A6/A7 internal pull-up resistors" class="smalltext">Sep 17, 2012, 03:20 pm</a>
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								<div class="inner" id="msg_926207">A6 and A7 are only inputs available to the mux in front of the ADC.&nbsp; There is no digital hardware behind the pins. <br /><br />Since the pull up is part of the digital latch, those two pins dont have pull ups (nor do they work as digital inputs.)<br /><br />Not that it is affecting your code, keep in mind that pinMode() has no effect on analog pins.</div>
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							<div class="signature" id="msg_926207_signature">Capacitor Expert By Day, Enginerd by night.&nbsp; ||&nbsp; Personal Blog: www.baldengineer.com&nbsp; || Electronics Tutorials for Beginners:&nbsp; www.addohms.com</div>
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								<div id="subject_926307" class="subject_title"><a href="https://forum.arduino.cc/index.php?topic=123176.msg926307#msg926307" rel="nofollow">Re: Arduino Nano - A6/A7 internal pull-up resistors</a></div>
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									<a href="https://forum.arduino.cc/index.php?topic=123176.msg926307#msg926307" rel="nofollow" title="Reply #2 - Re: Arduino Nano - A6/A7 internal pull-up resistors" class="smalltext">Sep 17, 2012, 05:04 pm</a>
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								<div class="inner" id="msg_926307">Thanks for the explanation. Makes sense, just wasn&#039;t so obvious for a newbie like me :-)<br /><br />Regarding pinMode(), that&#039;s curious. You mean it has no effect on A6/A7 because of their analog, input-only nature? <br /><br />Because the page http://arduino.cc/en/Tutorial/AnalogInputPins actually uses pinMode() on an analog pin. Ok, that&#039;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...<br /><br />cheers,<br />Aldo<br /></div>
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								<div id="subject_926462" class="subject_title"><a href="https://forum.arduino.cc/index.php?topic=123176.msg926462#msg926462" rel="nofollow">Re: Arduino Nano - A6/A7 internal pull-up resistors</a></div>
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									<a href="https://forum.arduino.cc/index.php?topic=123176.msg926462#msg926462" rel="nofollow" title="Reply #3 - Re: Arduino Nano - A6/A7 internal pull-up resistors" class="smalltext">Sep 17, 2012, 07:40 pm</a>
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								<div class="inner" id="msg_926462"><div class="quoteheader"><a href="https://forum.arduino.cc/index.php?topic=123176.msg926307#msg926307">Quote from: dadaumpa on Sep 17, 2012, 05:04 pm</a></div><blockquote class="bbc_standard_quote">Regarding pinMode(), that&#039;s curious. You mean it has no effect on A6/A7 because of their analog, input-only nature? <br /><br />Because the page http://arduino.cc/en/Tutorial/AnalogInputPins actually uses pinMode() on an analog pin. Ok, that&#039;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...</blockquote><div class="quotefooter"></div><br /><br />The first six analog pins do have digital circuitry behind them, so pinMode and digitalWrite work just fine. It&#039;s just pins A6 and A7 on the surface mount &#039;328 which are analog-only.<br /><br />Cheers!<br /></div>
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								<div id="subject_926727" class="subject_title"><a href="https://forum.arduino.cc/index.php?topic=123176.msg926727#msg926727" rel="nofollow">Re: Arduino Nano - A6/A7 internal pull-up resistors</a></div>
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									 #4 
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									<a href="https://forum.arduino.cc/index.php?topic=123176.msg926727#msg926727" rel="nofollow" title="Reply #4 - Re: Arduino Nano - A6/A7 internal pull-up resistors" class="smalltext">Sep 18, 2012, 12:11 am</a>
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								<div class="inner" id="msg_926727"><div class="quoteheader"><a href="https://forum.arduino.cc/index.php?topic=123176.msg926307#msg926307">Quote from: dadaumpa on Sep 17, 2012, 05:04 pm</a></div><blockquote class="bbc_standard_quote"><br />Regarding pinMode(), that&#039;s curious. You mean it has no effect on A6/A7 because of their analog, input-only nature? </blockquote><div class="quotefooter"></div><br />pinMode() has no effect on <em>analog</em> inputs (A0-A7).<br /><br />When analogRead() is called, the pin switches to an analog input regardless of what the pinMode was set as.<br /><br /><div class="quoteheader"><a href="https://forum.arduino.cc/index.php?topic=123176.msg926307#msg926307">Quote from: dadaumpa on Sep 17, 2012, 05:04 pm</a></div><blockquote class="bbc_standard_quote"><br />Because the page http://arduino.cc/en/Tutorial/AnalogInputPins actually uses pinMode() on an analog pin.</blockquote><div class="quotefooter"></div><br />Yes, because the code in that example is showing how to use the analog pin into a <em>digital</em> pin.</div>
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								<div id="subject_1586523" class="subject_title"><a href="https://forum.arduino.cc/index.php?topic=123176.msg1586523#msg1586523" rel="nofollow">Re: Arduino Nano - A6/A7 internal pull-up resistors</a></div>
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									 #5 
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									<a href="https://forum.arduino.cc/index.php?topic=123176.msg1586523#msg1586523" rel="nofollow" title="Reply #5 - Re: Arduino Nano - A6/A7 internal pull-up resistors" class="smalltext">Feb 11, 2014, 04:43 pm</a>
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								<div class="inner" id="msg_1586523">You can actually use A6 and A7 as &#039;digital&#039; pins with a little bit of logic in your code<br />below is my craptastic&nbsp; ]<img src="https://forum.arduino.cc/Smileys/arduino/cheesy.gif" alt="&#58;D" title="Cheesy" class="smiley"> example<br /><br /><div class="codeheader">Code: <a href="javascript:void(0);" onclick="return smfSelectText(this);" class="codeoperation">[Select]</a></div><code class="bbc_code">int pinStateA6 = 0;<br />int pinStateA7 = 0;<br /><br />void setup()<br />{<br />}<br /><br />void loop()<br />{<br />&nbsp; &nbsp; &nbsp;pinStateA6 = analogRead(A6) &gt; 100 ? 0 : 1;<br />&nbsp; &nbsp; &nbsp;pinStateA7 = analogRead(A7) &gt; 100 ? 0 : 1;<br />}</code></div>
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								<div id="subject_2341865" class="subject_title"><a href="https://forum.arduino.cc/index.php?topic=123176.msg2341865#msg2341865" rel="nofollow">Re: Arduino Nano - A6/A7 internal pull-up resistors</a></div>
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									<a href="https://forum.arduino.cc/index.php?topic=123176.msg2341865#msg2341865" rel="nofollow" title="Reply #6 - Re: Arduino Nano - A6/A7 internal pull-up resistors" class="smalltext">Aug 03, 2015, 05:37 pm</a>
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								<div class="inner" id="msg_2341865">pinMode can be used on A0-A5 to turn the internal pull-up resistor on or off.<br><br>&nbsp; &nbsp; pinMode(A0, INPUT_PULLUP);&nbsp; //on<br>&nbsp; &nbsp; pinMode(A0, INPUT);&nbsp; //off<br><br><br></div>
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								<div id="subject_2341961" class="subject_title"><a href="https://forum.arduino.cc/index.php?topic=123176.msg2341961#msg2341961" rel="nofollow">Re: Arduino Nano - A6/A7 internal pull-up resistors</a></div>
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									 #7 
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									<a href="https://forum.arduino.cc/index.php?topic=123176.msg2341961#msg2341961" rel="nofollow" title="Reply #7 - Re: Arduino Nano - A6/A7 internal pull-up resistors" class="smalltext">Aug 03, 2015, 07:03 pm</a>
									<span class="smalltext modified" id="modified_2341961"><span class="lastedit">Last Edit</span>: Aug 03, 2015, 07:08 pm by DrAzzy</span>
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								<div class="inner" id="msg_2341961">Sigh....<br><br>Analog pins A0~A5 are normal pins. You can refer to them as pins 14-19 as well, and they can be used normally as digital pins. <br><br>Analog pins A6 and A7 are weird. They can *only* be used for analogRead() - there aren&#39;t any registers to write to for them like there are for other pins. I get the impression they were an afterthought (maybe the DIP package was released first, then they&#39;re like &quot;hey we have some extra pins on TQFP32, let&#39;s connect them to the unused channels on the ADC mux&quot;)...<br><br>The next iteration of the x8 series (x8PB - only available up to 16k so far though) gives them proper treatment, putting them on a new port with those two pins, plus two pins that used to be a second set of power and ground pins, to make a 4 bit port. </div>
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