Datasheet

203
ATmega169A/PA/329A/PA/649A/P/3290A/PA/6490A/P [DATASHEET]
8284E–AVR–02/2013
22. Analog Comparator
22.1 Overview
The Analog Comparator compares the input values on the positive pin AIN0 and negative pin AIN1. When the volt-
age 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 PRADC, in ”PRR – Power Reduction Register” on page 45 must be written to zero to use the ADC input MUX.
Figure 22-1. Analog Comparator, block diagram
(2)
.
Note: 1. See Table 22-1 on page 203.
2. Refer to ”Pin configurations” on page 2 and Table 14-5 on page 74 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 ADC-
SRA 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 203. 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 multiplexed 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
1 0 011 ADC3
1 0 100 ADC4