Adc Conversion Result - Atmel ATtiny25 Manual

18.7

ADC Conversion Result

18.7.1 Single Ended Conversion
18.7.2 Unipolar Differential Conversion
7598H–AVR–07/09
Figure 18-12. Differential Non-linearity (DNL)
Output Code
0x3FF
0x000
• Quantization Error: Due to the quantization of the input voltage into a finite number of codes,
a range of input voltages (1 LSB wide) will code to the same value. Always ± 0.5 LSB.
• Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition compared to
an ideal transition for any code. This is the compound effect of offset, gain error, differential
error, non-linearity, and quantization error. Ideal value: ± 0.5 LSB.
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
Result Registers (ADCL, ADCH). The form of the conversion result depends on the type of the
conversio as there are three types of conversions: single ended conversion, unipolar differential
conversion and bipolar differential conversion.
For single ended conversion, the result is
⋅
V
1024
IN
ADC
= ---------------------------- -
V
REF
where V is the voltage on the selected input pin and V
IN
Table 18-3 on page 123
0x3FF represents the selected voltage reference minus one LSB. The result is presented in
one-sided form, from 0x3FF to 0x000.
If differential channels and an unipolar input mode are used, the result is
( ) ⋅
V V
–
POS NEG
ADC
---------------------------------------------------------- -
=
V
REF
1 LSB
0
and Table 18-4 on page
1024
⋅
GAIN
ATtiny25/45/85
V Input Voltage
REF
the selected voltage reference (see
REF
124). 0x000 represents analog ground, and
121