Datasheet

138
7701F–AVR–10/12
Atmel ATtiny24/44/84 [Preliminary]
Figure 18-1. Analog-to-Digital Converter Block Schematic
18.3 ADC Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approx-
imation. The minimum value represents GND, and the maximum value represents the
reference voltage. The voltage reference for the ADC may be selected by writing to the
REFS1..0 bits in the ADMUX register. The VCC supply, the AREF pin or an internal 1.1V volt-
age reference may be selected as the ADC voltage reference.
The analog input channel and differential gain are selected by writing to the MUX5..0 bits in
the ADMUX register. Any of the eight ADC input pins ADC7..0 can be selected as sin-
gle-ended inputs to the ADC. For differential measurements, all adjacent analog inputs can be
selected as an input pair. Every input can also be measured with ADC3. These pairs of differ-
ential inputs are measured by the ADC through the differential gain amplifier.
ADC CONVERSION
COMPLETE IRQ
8-BIT DATA BUS
15 0
ADC MULTIPLEXER
SELECT (ADMUX)
ADC CTRL. & STATUS A
REGISTER (ADCSRA)
ADC DATA REGISTER
(ADCH/ADCL)
ADIE
ADATE
ADSC
ADE
N
ADIF
ADIF
MUX4...MUX0
ADPS0
ADPS1
ADPS2
CONVERSION LOGIC
10-BIT DAC
+
-
SAMPLE & HOLD
COMPARATOR
INTERNAL
REFERENCE
1.1V
MUX DECODER
V
CC
ADC7
ADC6
ADC5
ADC4
REFS1..REFS0
ADLAR
CHANNEL SELECTION
ADC[9:0]
ADC MULTIPLEXER
OUTPUT
PRESCALER
TRIGGER
SELECT
ADTS2...ADTS0
INTERRUPT
FLAGS
START
+
-
GAIN SELECTION
GAIN
AMPLIFIER
NEG.
INPUT
MUX
SINGLE ENDED / DIFFERENTIAL SELECTION
TEMPERATURE
SENSOR
ADC8
BIN
IPR
ADC3
ADC2
ADC1
ADC0
POS.
INPUT
MUX
AGND
ADC CTRL. & STATUS B
REGISTER (ADCSRB)
AREF