ATMEGA640 datasheet(269/436 Pages) MICROCHIP

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269

ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

Figure 26-1. Analog to Digital Converter Block Schematic

26.2 Operation

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

mum value represents GND and the maximum value represents the voltage on the AREF pin minus 1 LSB.

Optionally, AVCC or an internal 1.1V or 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 is selected by writing to the MUX bits in ADMUX and ADCSRB. 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 amplifier.

If differential channels are selected, the voltage difference between the selected input channel pair then becomes

the analog input to the ADC. If single ended channels are used, the amplifier is bypassed altogether.

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]

ADC[15:0]

10-bit DAC

ADC[10:8]

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