Rainbow Electronics ATmega3290P_V - Manual (Page 214)

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ATmega329/3290/649/6490
2552H–AVR–11/06
Figure 97. Differential Measurement Range
ADMUX = 0xFB (ADC3 - ADC2, 1.1V reference, left adjusted result)
Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.
ADCR = 512 * (300 - 500) / 1100 = -93 = 0x3A3.
ADCL will thus read 0xC0, and ADCH will read 0xD8. Writing zero to ADLAR right
adjusts the result: ADCL = 0xA3, ADCH = 0x03.
Table 94. Correlation Between Input Voltage and Output Codes
V
ADCn
Read Code Corresponding Decimal Value
V
ADCm
+ V
REF
0x1FF 511
V
ADCm
+ 511 /
512
V
REF
0x1FF 511
V
ADCm
+ 510 /
512
V
REF
0x1FE 510
... ... ...
V
ADCm
+ 1 /
512
V
REF
0x001 1
V
ADCm
0x000 0
V
ADCm
- 1 /
512
V
REF
0x3FF -1
... ... ...
V
ADCm
- 511 /
512
V
REF
0x201 -511
V
ADCm
- V
REF
0x200 -512
0
Output Code
0x1FF
0x000
V
REF
Differential Input
Voltage (Volts)
0x3FF
0x200
- V
REF