ATtiny25 datasheet(112/196 Pages) ATMEL

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112

7598H–AVR–07/09

ATtiny25/45/85

Figure 18-1. Analog to Digital Converter Block Schematic

18.2

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 MUX3..0 bits in

ADMUX. Any of the four ADC input pins ADC3..0 can be selected as single ended inputs to the

ADC. ADC2 or ADC0 can be selected as positive input and ADC0, ADC1, ADC2 or ADC3 can

be selected as negative input to the differential gain amplifier.

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

between the selected input pair by the selected gain factor, 1x or 20x, according to the setting of

the MUX3..0 bits in ADMUX. 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 A

ADC DATA REGISTER

(ADCH/ADCL)

CONVERSION LOGIC

10-BIT DAC

SAMPLE & HOLD

COMPARATOR

INTERNAL 1.1V/2.56V

REFERENCE

MUX DECODER

AREF

ADC3

ADC2

ADC1

ADC0

ADC MULTIPLEXER

OUTPUT

PRESCALER

INPUT

MUX

TRIGGER

SELECT

ADTS[2:0]

INTERRUPT

FLAGS

START

GAIN

AMPLIFIER

NEG.

INPUT

MUX

SINGLE ENDED / DIFFERENTIAL SELECTION

TEMPERATURE

SENSOR

ADC4

ADC CTRL. & STATUS B

BIN

IPR

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