123
ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
Figure 17-1. Analog to Digital Converter Block Schematic
17.3
Operation
The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The mini-
mum value represents GND and the maximum value represents the voltage on V
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 REFS[2:0] 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. Option-
ally the internal 2.56V voltage reference may 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[3:0] bits in ADMUX. Any of the
four ADC input pins ADC[3:0] 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 MUX[3:0] bits in ADMUX.
This amplified value then becomes the analog input to the ADC. If single ended channels are used, the gain ampli-
fier is bypassed altogether.
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
ADEN
ADIF
MUX1
MUX0
ADPS0
ADPS1
ADPS2
CONVERSION LOGIC
10-BIT DAC
+
-
SAMPLE & HOLD
COMPARATOR
INTERNAL 1.1V/2.56V
REFERENCE
MUX DECODER
MUX2
AREF
ADC3
ADC2
ADC1
ADC0
REFS[2:0]
ADLAR
CHANNEL
SELECTION
ADC[9:0]
ADC MULTIPLEXER
OUTPUT
PRESCALER
INPUT
MUX
TRIGGER
SELECT
ADTS[2:0]
INTERRUPT
FLAGS
START
+
-
GAIN
SELECTION
GAIN
AMPLIFIER
NEG.
INPUT
MUX
SINGLE ENDED / DIFFERENTIAL SELECTION
TEMPERATURE
SENSOR
ADC4
ADC CTRL. & STATUS B
REGISTER (ADCSRB)
BIN
IPR
V
CC