Atmel ATmega8535, Руководство пользователя

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218
ATmega8535(L)
2502K–AVR–10/06
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 refer-
ence (see Table 84 on page 219 and Table 85 on page 220). 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 the bit is one, the result is
negative, and if the bit is zero, the result is positive. Figure 111 shows the decoding of
the differential input range.
Table 83 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 111. 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