ATmega328P datasheet(246/448 Pages) ATMEL

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246

8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

22. 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 com-

parator 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 ”Minimizing Power Consumption” on page 42 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 247.

2. Refer to Figure 1-1 on page 2 and Table 13-9 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 Com-

parator. 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. 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)

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