user14589: I am (currently) parsing a PPM analog signal using an Arduino Uno R3 using the analog comparator ASCR and analog hardware interrupts using AIN0 and AIN1. I am applying a specific negative comparison voltage using a linear voltage regulator on AIN0 and the signal on AIN1.
Code snippets:
setup
  ACSR  = B00011011;

outside other closures
ISR(ANALOG_COMP_vect) {
   CRCArduinoPPMChannels::INT0ISR();
}

I am trying to move this project to an Arduino (compatible) Pro Micro from SparkFun. The datasheet specifies AIN0 on ATmega32u4 pin 1 but do not see a reference to AIN1. 
The datasheet outlines use of the analog comparator on page 289:

AIN+ can be connected either to the AIN0 (PE6) pin, or to the internal
  Bandgap reference. AIN- can only be connected to the ADC multiplexer.

I have connected the signal to Arduino pin 7, the comparison voltage to Arduino pin 20 (analog 2) and set the following options of the ADMUX register:
ADMUX = B11000101;

The interrupts trigger but the comparator voltage (AIN-) is not being observed. Any help would be appreciated.

user368: AIN- won't be connected to the ADC mux unless ACME is set and ADEN is cleared. Don't forget to do so.

14589: <p>I am (currently) parsing a PPM analog signal using an Arduino Uno R3 using the analog comparator ASCR and analog hardware interrupts using AIN0 and AIN1. I am applying a specific negative comparison voltage using a linear voltage regulator on AIN0 and the signal on AIN1.</p>

<p><strong>Code snippets:</strong></p>

<p><em>setup</em></p>

<pre><code>  ACSR  = B00011011;
</code></pre>

<p><em>outside other closures</em></p>

<pre><code>ISR(ANALOG_COMP_vect) {
   CRCArduinoPPMChannels::INT0ISR();
}
</code></pre>

<p>I am trying to move this project to an Arduino (compatible) <a href="https://www.sparkfun.com/products/12640" rel="nofollow noreferrer">Pro Micro from SparkFun</a>. The <a href="http://cdn.sparkfun.com/datasheets/Dev/Arduino/Boards/ATMega32U4.pdf" rel="nofollow noreferrer">datasheet</a> specifies AIN0 on ATmega32u4 pin 1 but do not see a reference to AIN1. </p>

<p>The datasheet outlines use of the analog comparator on page 289:</p>

<blockquote>
  <p>AIN+ can be connected either to the AIN0 (PE6) pin, or to the internal
  Bandgap reference. AIN- can only be connected to the ADC multiplexer.</p>
</blockquote>

<p>I have connected the signal to Arduino pin 7, the comparison voltage to Arduino pin 20 (analog 2) and set the following options of the ADMUX register:</p>

<pre><code>ADMUX = B11000101;
</code></pre>

<p>The interrupts trigger but the comparator voltage (AIN-) is not being observed. Any help would be appreciated.</p>
 368: <p>AIN- won't be connected to the ADC mux unless ACME is set and ADEN is cleared. Don't forget to do so.</p>
