Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 255
23.8 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
where V
IN
is the voltage on the selected input pin and V
REF
the selected voltage reference (see Table 23-3 on
page 257 and Table 23-4 on page 257). 0x000 represents analog ground, and 0x3FF represents the selected
reference voltage minus one LSB.
If differential channels are used, the result is
where V
POS
is the voltage on the positive input pin, V
NEG
the voltage on the negative input pin, GAIN the
selected gain factor, and V
REF
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
results, it is sufficient to read the MSB of the result (ADC9 in ADCH). If this bit is one, the result is negative, and
if this bit is zero, the result is positive. Figure 23-14 on page 255 shows the decoding of the differential input
range.
Table 23-2 on page 256 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 V
REF
.
Figure 23-14. Differential measurement range
ADC
V
IN
1024
V
REF
--------------------------=
ADC
V
POS
V
NEG
–GAIN 512
V
REF
------------------------------------------------------------------------=
0
Output Code
0x1FF
0x000
V
REF
/GAIN
Differential Input
Voltage (Volts)
0x3FF
0x200
- V
REF
/GAIN