ATMEGA640 datasheet(280/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

26.7 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 VIN is the voltage on the selected input pin and VREF the selected voltage reference (see Table 26-3 on page

281 and Table 26-4 on page 282). 0x000 represents analog ground, and 0x3FF represents the selected reference

voltage minus one LSB.

If differential channels are used, the result is

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, the result is positive. Figure

26-15 shows the decoding of the differential input range.

Table 26-2 on page 281 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.

Figure 26-15. Differential Measurement Range

ADC

VIN 1024



VREF

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

ADC

VPOS VNEG

–

 512



VREF

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

Output Code

0x1FF

0x000

REF

Differential Input

Voltage (Volts)

0x3FF

0x200

- V

REF

ATMEGA640 Datasheet(PDF) 280 Page - Microchip Technology