attiny25v ATMEL Corporation, attiny25v Datasheet - Page 127

• Manufacturer Part Number: attiny25v
• Description: Microcontroller With 2/4/8k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

17.3
2586K–AVR–01/08
Operation
Figure 17-1. Analog to Digital Converter Block Schematic
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
V
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 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 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.
ADC3
ADC2
ADC1
ADC0
AREF
V
CC
CC
, the voltage on the AREF pin or an internal 1.1V / 2.56V voltage reference.
INTERNAL 1.1V/2.56V
TEMPERATURE
8-BIT DATA BUS
ADC CTRL. & STATUS B
REFERENCE
SENSOR
REGISTER (ADCSRB)
ADC4
INPUT
INPUT
MUX
NEG.
MUX
ADC MULTIPLEXER
SELECT (ADMUX)
MUX DECODER
+
-
SINGLE ENDED / DIFFERENTIAL SELECTION
GAIN
AMPLIFIER
10-BIT DAC
ADC CTRL. & STATUS A
REGISTER (ADCSRA)
ADC CONVERSION
COMPLETE IRQ
PRESCALER
CONVERSION LOGIC
ADTS[2:0]
ATtiny25/45/85
INTERRUPT
TRIGGER
FLAGS
SELECT
SAMPLE & HOLD
COMPARATOR
15
+
-
ADC DATA REGISTER
(ADCH/ADCL)
ADC MULTIPLEXER
OUTPUT
0
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