28.9.1 ADC Multiplexer Selection Register
| Name: | ADMUX |
| Offset: | 0x7C |
| Reset: | 0x00 |
| Property: | - |
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| REFS [1:0] | ADLAR | MUX [3:0] | |||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | ||
| Reset | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||
Bits 7:6 – REFS [1:0] Reference Selection
These bits select the voltage reference for the ADC. If these bits are changed during a conversion, the change will not go into effect until this conversion is complete (ADIF in ADCSRA is set). The internal voltage reference options may not be used if an external reference voltage is being applied to the AREF pin.
| REFS[1:0] | Voltage Reference Selection |
|---|---|
| 00 | AREF, Internal Vref turned OFF |
| 01 | AVCC with external capacitor at AREF pin |
| 10 | Reserved |
| 11 | Internal 1.1V voltage reference with external capacitor at AREF pin |
Bit 5 – ADLAR ADC Left Adjust Result
Bits 3:0 – MUX [3:0] Analog Channel Selection
The value of these bits selects which analog inputs are connected to the ADC. If these bits are changed during a conversion, the change will not go in effect until this conversion is complete (ADIF in ADCSRA is set).
| MUX[3:0] | Single Ended Input |
|---|---|
| 0000 | ADC0 |
| 0001 | ADC1 |
| 0010 | ADC2 |
| 0011 | ADC3 |
| 0100 | ADC4 |
| 0101 | ADC5 |
| 0110 | ADC6 |
| 0111 | ADC7 |
| 1000 | Temperature sensor |
| 1001 | Reserved |
| 1010 | Reserved |
| 1011 | Reserved |
| 1100 | Reserved |
| 1101 | Reserved |
| 1110 | 1.1V (VBG) |
| 1111 | 0V (GND) |