ATtiny261-ESSZ datasheet(145/227 Pages) ATMEL

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145

7753C–AVR–07/09

ATtiny261/ATtiny461/ATtiny861

Figure 19-1. Analog to Digital Converter Block Schematic

19.3

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

CC, the voltage on the AREF pin or an internal 1.1V / 2.56V voltage reference.

The voltage reference for the ADC may be selected by writing to the REFS2..0 bits in ADMUX.

The VCC supply, the AREF pin or an internal 1.1V / 2.56V voltage reference may be selected as

the ADC voltage reference. Optionally the internal 1.1V / 2.56V voltage reference may be decou-

pled 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 MUX5..0 bits in

ADMUX. Any of the 11 ADC input pins ADC10..0 can be selected as single ended inputs to the

ADC. The positive and negative inputs to the differential gain amplifier are described in Table

19-5.

If differential channels are selected, the differential gain stage amplifies the voltage difference

between the selected input pair by the selected gain factor, 1x, 8x, 20x or 32x, according to the

setting of the MUX5..0 bits in ADMUX and the GSEL bit in ADCSRB. This amplified value then

becomes the analog input to the ADC. If single ended channels are used, the gain amplifier is

bypassed altogether.

ADC CONVERSION

COMPLETE IRQ

8-BIT DATA BUS

ADC MULTIPLEXER

SELECT (ADMUX)

ADC CTRL. & STATUS

ADC DATA REGISTER

(ADCH/ADCL)

CONVERSION LOGIC

10-BIT DAC

SAMPLE & HOLD

COMPARATOR

MUX DECODER

ADC7

ADC6

ADC5

ADC4

ADC3

ADC2

ADC1

ADC0

ADC

MULTIPLEXER OUTPUT

GAIN

AMPLIFIER

INTERNAL 1.18V

REFERENCE

PRESCALER

SINGLE ENDED /

DIFFERENTIAL SELECTION

AGND

POS.

INPUT

MUX

NEG.

INPUT

MUX

ADC10

ADC9

ADC8

VCC

AREF

TEMPERATURE

SENSOR

INTERNAL 2.56/1.1V

REFERENCE

MUX

ADC CTRL. & STATUS

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