Using Analog Comparator on ATmega32u4 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.
AIN- won't be connected to the ADC mux unless ACME is set and ADEN is cleared. Don't forget to do so.