Datasheet

190
ATmega8A [DATASHEET]
8159E–AVR–02/2013
• Differential Non-linearity (DNL): The maximum deviation of the actual code width (the interval between two
adjacent transitions) from the ideal code width (1LSB). Ideal value: 0LSB.
Figure 23-11. Differential Non-linearity (DNL)
• Quantization Error: Due to the quantization of the input voltage into a finite number of codes, a range of input
voltages (1LSB wide) will code to the same value. Always ±0.5LSB.
• 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: ±0.5LSB.
23.7 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC Result Registers
(ADCL, ADCH).
For single ended conversion, the result is
where V
IN
is the voltage on the selected input pin and V
REF
the selected voltage reference (see Table 23-2 on page
191 and Table 23-3 on page 191). 0x000 represents ground, and 0x3FF represents the selected reference voltage
minus one LSB.
23.8 Register Description
23.8.1 ADMUX – ADC Multiplexer Selection Register – ADMUX
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 23-2. If these bits are changed during a
conversion, the change will not go in effect until this conversion is complete (ADIF in ADCSRA is set). The internal
voltage reference options may not be used if an external reference voltage is being applied to the AREF pin.
Output Code
0x3FF
0x000
0
V
REF
Input Voltage
DNL
1 LSB
ADC
V
IN
1024
V
REF
--------------------------=
Bit 76543210
REFS1 REFS0 ADLAR – MUX3 MUX2 MUX1 MUX0 ADMUX
Read/Write R/W R/W R/W R R/W R/W R/W R/W
Initial Value00000000