ATmega1284P datasheet(253/380 Pages) ATMEL

253 / 380 page

253

8059D–AVR–11/09

ATmega1284P

21.8

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 VREF the selected voltage reference (see

Table 21-3 on page 255 and Table 21-4 on page 256). 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, VNEG 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 posi-

tive. Figure 21-14 on page 254 shows the decoding of the differential input range.

Table 21-2 on page 254 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.

ADC

1024

⋅

REF

--------------------------

ADC

POS

NEG

–

() GAIN 512

⋅⋅

REF

------------------------------------------------------------------------

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