ADMUX

Bit7	6	5	4	3	2	1	0
REFS [1:0]		ADLAR		MUX [3:0]
AccessR/W	R/W	R/W		R/W	R/W	R/W	R/W
Reset0	0	0		0	0	0	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.

Table 1. ADC Voltage Reference Selection
REFS[1:0]	Voltage Reference Selection
00	AREF, Internal V_refturned OFF
01	AV_CC with external capacitor at AREF pin
10	Reserved
11	Internal 1.1V voltage reference with external capacitor at AREF pin

ADC Left Adjust Result

The ADLAR bit affects the presentation of the ADC conversion result in the ADC data register. Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing the ADLAR bit will affect the ADC data register immediately, regardless of any ongoing conversions. For a complete description of this bit, refer to ADCL and ADCH.

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).

Table 2. Input Channel Selection
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 (V_BG)
1111	0V (GND)

Bits 7:6 – REFS [1:0]: Reference Selection

Bit 5 – ADLAR: ADC Left Adjust Result

Bits 3:0 – MUX [3:0]: Analog Channel Selection