ADC Multiplexer Selection Register

Name:: ADMUX
Offset:: 0x1B
Reset:: 0x00
Access:: -

Bit7	6	5	4	3	2	1	0
REFSn[1:0]					MUXn[2:0]
AccessR/W	R/W				R/W	R/W	R/W
Reset0	0				0	0	0

Bits 7:6 – REFSn: Reference Selection [n = 1:0]

Reference Selection [n = 1:0]

These bits select the voltage reference for 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. ADC Voltage Reference Selection
REFS[1:0]	Voltage Reference Selection
00	V_cc
01	Internal 1.1V reference
10	Internal 2.2V reference
11	Internal 4.3V reference

Bits 2:0 – MUXn: Analog Channel Selection [n = 2:0]

Analog Channel Selection [n = 2:0]

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 (ADCSRA.ADIF is set).

Table 1. Input Channel Selection
MUX[2:0]	Single Ended Input	Pin name
000	ADC0	PA[0]
001	ADC1	PA[1]
010	ADC2	PA[5]
011	ADC3	PA[6]
100	ADC4	PB[0]
101	ADC5	PB[1]
110	ADC6	PB[2]
111	ADC7	PB[3]