ATmega1284P datasheet(241/380 Pages) ATMEL

241 / 380 page

241

8059D–AVR–11/09

ATmega1284P

Figure 21-1. Analog-to-digital Converter Block Schematic

21.3

Operation

The ADC converts an analog input voltage to a 10-bit digital value through successive approxi-

mation. The minimum value represents GND and the maximum value represents the voltage on

the AREF pin minus 1 LSB. Optionally, AVCC or an internal 2.56V reference voltage may be

connected to the AREF pin by writing to the REFSn bits in the ADMUX Register. The internal

voltage reference may thus be decoupled by an external capacitor at the AREF pin to improve

noise immunity.

The analog input channel and differential gain are selected by writing to the MUX bits in

ADMUX. Any of the ADC input pins, as well as GND and a fixed bandgap voltage reference, can

be selected as single ended inputs to the ADC. A selection of ADC input pins can be selected as

positive and negative inputs to the differential gain amplifier.

ADC CONVERSION

COMPLETE IRQ

8-BIT DATABUS

SAMPLE & HOLD

COMPARATOR

INTERNAL

REFERENCE

(1.1V/2.56V)

AVCC

ADC

MULTIPLEXER

OUTPUT

GAIN

AMPLIFIER

AREF

BANDGAP (1.1V)

REFERENCE

GND

CONVERSION LOGIC

ADC CTRL & STATUS

PRESCALER

ADC MULTIPLEXER

SELECT (ADMUX)

MUX DECODER

ADC DATA REGISTER

(ADCH/ADCL)

ADC[2:0]

TRIGGER

SELECT

START

INTERRUPT

FLAGS

ADTS[2:0]

NEG

INPUT

MUX

POS

INPUT

MUX

ADC[7:0]

10-bit DAC

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