Rainbow Electronics ATmega64C1 - Manual (Page 239)

239
7647A–AVR–02/08
ATmega32/64/M1/C1
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 18-14. Differential Measurement Range
Example 1:
– ADMUX = 0xED (ADC3 - ADC2, 10x gain, 2.56V reference, left adjusted result)
– Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.
– ADCR = 512 * 10 * (300 - 500) / 2560 = -400 = 0x270
Table 18-2. Correlation Between Input Voltage and Output Codes
V
ADCn
Read code Corresponding decimal value
V
ADCm
+ V
REF
/GAIN 0x1FF 511
V
ADCm
+ 0.999 V
REF
/GAIN 0x1FF 511
V
ADCm
+ 0.998 V
REF
/GAIN 0x1FE 510
... ... ...
V
ADCm
+ 0.001 V
REF
/GAIN 0x001 1
V
ADCm
0x000 0
V
ADCm
- 0.001 V
REF
/GAIN 0x3FF -1
... ... ...
V
ADCm
- 0.999 V
REF
/GAIN 0x201 -511
V
ADCm
- V
REF
/GAIN 0x200 -512
0
Output Code
0x1FF
0x000
V
REF
Differential Input
Voltage (Volts)
0x3FF
0x200
- V
REF
/Gain /Gain