Datasheet

27.8.1 ADMUX – ADC Multiplexer Selection Register
Name: ADMUX
Offset: 0x07
Reset: 0x00
Property: When addressing I/O Registers as data space the offset address is 0x27
When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When
addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these offset
addresses.
Bit 7 6 5 4 3 2 1 0
REFSn[1:0] ADLAR MUXn[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 – REFSn[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). The internal
voltage reference options may not be used if an external reference voltage is being applied to the AREF
pin.
Table 27-2. ADC Voltage Reference Selection
REFS[1:0] Voltage Reference Selection
00 AREF, Internal V
ref
turned off
01 AV
CC
with external capacitor at AREF pin
10 Reserved
11 Internal 2.56V Voltage Reference with external capacitor at AREF pin
Bit 5 – ADLAR 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, see ADCL and ADCH.
Bits 3:0 – MUXn[3:0] Analog Channel Selection [n = 3:0]
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 (ADIF in ADCSRA is
set).
Table 27-3. Input Channel Selection
MUX[3:0] Single Ended Input
0000 ADC0
0001 ADC1
0010 ADC2
AVR 8-Bit Microcontroller
ADC - Analog to Digital Converter
© 2017 Microchip Technology Inc.
Datasheet Complete
40001974A-page 264