Rainbow Electronics Atmega169L - Manual (Page 203)

203
ATmega169V/L
2514A–AVR–08/02
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 89 on page 204 and Table 90 on page 205). 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, and V
REF
the selected voltage reference. The result is presented in two’s com-
plement 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 95 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 95. Differential Measurement Range
ADC
V
I N
1024
⋅
V
REF
-------------------------- =
ADC
V
POS
V
NEG
–
( ) 512 ⋅
V
REF
----------------------------------------------------- =
0
Output Code
0x1FF
0x000
V
REF
Differential Input
Voltage (Volts)
0x3FF
0x200
- V
REF