Rainbow Electronics ATmega128L - Manual (Page 232)

232
ATmega128(L)
2467B–09/01
where V
IN
is the voltage on the selected input pin and V
REF
the selected voltage refer-
ence (see Table 96 on page 233 and Table 97 on page 234). 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). There are no leading 1's above the MSB / sign bit, even if the result is negative.
Figure 118 shows the decoding of the differential input range.
Table 95 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 118. 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