Datasheet
293
ATmega640/1280/1281/2560/2561
2549K–AVR–01/07
Example:
ADMUX = 0xFB (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.
ADCL will thus read 0x00, and ADCH will read 0x9C. Writing zero to ADLAR right
adjusts the result: ADCL = 0x70, ADCH = 0x02.
Table 127. 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