The analog comparator evaluates the input values on the positive pin AIN0 and negative pin AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin AIN1, the Analog Comparator Output (ACO) is set. The comparator’s output can be set to trigger the Timer/Counter1 input capture function. In addition, the comparator can trigger a separate interrupt, exclusive to the analog comparator. The user can select Interrupt triggering on comparator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown below.

The power reduction ADC bit in the Power Reduction Register (PRR0.PRADC) must be written to '0' in order to be able to use the ADC input MUX.

Figure 1. Analog Comparator Block Diagram
Note: Refer to the Pin Configuration and the I/O Ports description for Analog Comparator pin placement