AT90USB646 datasheet(328/434 Pages) ATMEL

328 / 434 page

328

7593A–AVR–02/06

AT90USB64/128

where V

IN is the voltage on the selected input pin and VREF the selected voltage reference (see

Table 25-3 on page 330 and Table 25-4 on page 330). 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 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 posi-

tive. Figure 25-14 shows the decoding of the differential input range.

Table 82 shows the resulting output codes if the differential input channel pair (ADCn - ADCm) is

selected with a reference voltage of V

REF.

Figure 25-14. Differential Measurement Range

ADC

1023

⋅

REF

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

ADC

POS

NEG

–

() GAIN 512

⋅⋅

REF

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

Output Code

0x1FF

0x000

REF

Differential Input

Voltage (Volts)

0x3FF

0x200

- V

REF

AT90USB646 Datasheet(PDF) 328 Page - ATMEL Corporation

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