18.7 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:
V
1023
IN
------------------------
ADC =
V
REF
where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see Table 18-4 on page 210 and
Table 18-5 on page 211). 0x000 represents analog ground, and 0x3FF represents the selected reference voltage.
If differential channels are used, the result is:
V
– V
GAIN 512
NEG
POS
-----------------------------------------------------------------------
ADC =
V
REF
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin, GAIN the selected gain factor
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, the result is positive. Figure 18-13
shows the decoding of the differential input range.
Table 18-2 on page 208 shows the resulting output codes if the differential input channel pair (ADCn - ADCm) is selected
with a reference voltage of VREF
.
Figure 18-13. Differential Measurement Range
Output Code
0x1FF
0x000
0x3FF
0
V
/Gain
V
/Gain Differential Input
Voltage (Volts)
REF
REF
0x200
ATmega16/32/64/M1/C1 [DATASHEET]
207
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
