Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 244
Figure 23-1. Analog-to-digital Converter block schematic
23.3 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 1LSB.
Optionally, AV
CC
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.
If differential channels are selected, the differential gain stage amplifies the voltage difference between the
selected input channel pair by the selected gain factor. 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 DATABUS
15 0
ADIE
ADATE
ADSC
ADEN
ADIF
ADIF
MUX[4:0]
ADPS[2:0]
SAMPLE & HOLD
COMPARATOR
INTERNAL
REFERENCE
(1.1V/2.56V)
AVCC
REFS[1:0]
ADLAR
CHANNEL SELECTION
ADC[9:0]
ADC
MULTIPLEXER
OUTPUT
GAIN
AMPLIFIER
AREF
BANDGAP (1.1V)
REFERENCE
GND
CONVERSION LOGIC
ADC CTRL & STATUS
REGISTER B (ADCSRB)
ADC CTRL & STATUS
REGISTER A (ADCSRA)
PRESCALER
ADC MULTIPLEXER
SELECT (ADMUX)
MUX DECODER
DIFF / GAIN SELECT
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