Operation, Atmega169v/l – Rainbow Electronics Atmega169L User Manual

Page 192

192

ATmega169V/L

2514A–AVR–08/02

Figure 82. Analog to Digital Converter Block Schematic

Operation

The ADC converts an analog input voltage to a 10-bit digital value through successive
approximation. The minimum value represents GND and the maximum value represents
the voltage on the AREF pin minus 1 LSB. Optionally, AVCC or an internal 1.1V refer-
ence 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. 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.

The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA. Voltage refer-
ence and input channel selections will not go into effect until ADEN is set. The ADC
does not consume power when ADEN is cleared, so it is recommended to switch off the
ADC before entering power saving sleep modes.

ADC CONVERSION

COMPLETE IRQ

8-BIT DATA BUS

ADC MULTIPLEXER

SELECT (ADMUX)

ADC CTRL. & STATUS

ADC DATA REGISTER

(ADCH/ADCL)

MUX2

ADIE

ADATE

ADSC

ADEN

ADIF

MUX1

MUX0

ADPS0

ADPS1

ADPS2

MUX3

CONVERSION LOGIC

10-BIT DAC

SAMPLE & HOLD
COMPARATOR

INTERNAL

REFERENCE

MUX DECODER

MUX4

AVCC

ADC7

ADC6

ADC5

ADC4

ADC3

ADC2

ADC1

ADC0

REFS0

REFS1

ADLAR

CHANNEL SELECTION

GAIN SELECTION

ADC[9:0]

ADC MULTIPLEXER
OUTPUT

DIFFERENTIAL
AMPLIFIER

AREF

BANDGAP

REFERENCE

PRESCALER

SINGLE ENDED / DIFFERENTIAL SELECTION

GND

POS.

INPUT

MUX

NEG.

INPUT

MUX

TRIGGER

SELECT

ADTS[2:0]

INTERRUPT

FLAGS

ADHSM

START