Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 240
22. AC - Analog Comparator
22.1 Overview
The Analog Comparator compares 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 in Figure 22-1.
The Power Reduction ADC bit, PRADC, in ”PRR0 – Power Reduction Register 0” on page 56 must be disabled
by writing a logical zero to be able to use the ADC input MUX.
Figure 22-1. Analog Comparator block diagram
(2)
Notes: 1. See Table 22-1 on page 240.
2. Refer to Figure 1-1 on page 11 and Table 14-5 on page 88 for Analog Comparator pin placement
22.2 Analog Comparator Multiplexed Input
It is possible to select any of the ADC7..0 pins to replace the negative input to the Analog Comparator. The ADC
multiplexer is used to select this input, and consequently, the ADC must be switched off to utilize this feature. If
the Analog Comparator Multiplexer Enable bit (ACME in ADCSRB) is set and the ADC is switched off (ADEN in
ADCSRA is zero), MUX2..0 in ADMUX select the input pin to replace the negative input to the Analog
Comparator, as shown in Table 22-1 on page 240. If ACME is cleared or ADEN is set, AIN1 is applied to the
negative input to the Analog Comparator.
ACBG
BANDGAP
REFERENCE
ADC MULTIPLEXER
OUTPUT
ACME
ADEN
(1)
Table 22-1. Analog Comparator Mulitiplexed input
ACME ADEN MUX2..0 Analog Comparator negative input
0 x xxx AIN1
1 1 xxx AIN1
1 0 000 ADC0
1 0 001 ADC1
1 0 010 ADC2