Rainbow Electronics ATtiny26L - Manual (Page 78)

78
ATtiny26(L)
1477B–AVR–04/02
Figure 46. 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 and internal 2.56V refer-
ence voltage may be connected to the AREF pin by writing to the REFS bits in ADMUX.
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 11 ADC input pins ADC10..0, as well as GND and a fixed bandgap
voltage reference of nominally 1.18V (V
BG
), 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 dif-
ference between the selected input channel pair by the selected gain factor. Note that
the voltage on the positive input terminal must be higher than on the negative input ter-
ADC CONVERSION
COMPLETE IRQ
8-BIT DATA BUS
15 0
ADC MULTIPLEXER
SELECT (ADMUX)
ADC CTRL. & STATUS
REGISTER (ADCSR)
ADC DATA REGISTER
(ADCH/ADCL)
MUX2
ADIE
ADFR ADSC ADEN ADIF
ADIF
MUX1 MUX0
ADPS0 ADPS1 ADPS2
MUX3
CONVERSION LOGIC
10-BIT DAC
+
-
SAMPLE & HOLD
COMPARATOR
MUX DECODER
MUX4
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
REFS0 REFS1 ADLAR
+
-
CHANNEL SELECTION
GAIN SELECTION
ADC[9:0]
ADC
MULTIPLEXER OUTPUT
GAIN
AMPLIFIER
INTERNAL 1.18 V
REFERENCE
PRESCALER
SINGLE ENDED /
DIFFERENTIAL SELECTION
GND
POS.
INPUT
MUX
NEG.
INPUT
MUX
ADC10
ADC9
ADC8
INTERNAL
2.56 V
REFERENCE
VCC
AREF