
456
42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
Figure 27-15. Differential Non-linearity (DNL)
Output Code
0x3FF
0x000
0
VREF Input Voltage
DNL
1 LSB
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. It is
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.
27.8 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
REF
IN
V
ADC
1024
=
where VIN is the voltage on the selected input pin and VREF the selected voltage
represents analog ground, and 0x3FF represents the selected reference voltage minus
one LSB.
If differential channels are used, the result is
(
)
REF
NEG
POS
V
GAIN
V
ADC
512
=
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative
input pin, and VREF the selected voltage reference. The result is presented in two’s
complement form, from 0x200 (-512d) through 0x1FF (+511d). Note that if the user
wants to perform a quick polarity check of the result, it is sufficient to read the MSB of
the result (ADC9 in ADCH). If the bit is one, the result is negative, and if this bit is zero,
input range.
Table 27-7 below shows the resulting output codes if the differential input channel pair
(ADCn - ADCm) is selected with a gain of GAIN and a reference voltage of VREF.