Datasheet

25.8.1. ADC Multiplexer Selection Register

Name: ADMUX

Offset: 0x7C

Reset: 0x00

Property:

Bit 7 6 5 4 3 2 1 0

REFS1 REFS0 ADLAR MUX4 MUX3 MUX2 MUX1 MUX0

Access

R/W R/W R/W R/W R/W R/W R/W R/W

Reset 0 0 0 0 0 0 0 0

Bits 7:6 – REFSn: 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 25-3. ADC Voltage Reference Selection

REFS[1:0] Voltage Reference Selection

00 AREF, Internal V

ref

turned off

01 AV

with external capacitor at AREF pin

10 Internal 1.1V Voltage Reference with external capacitor at AREF pin

11 Internal 2.56V Voltage Reference with external capacitor at AREF pin

Note: If differential channels are selected, only 2.56V should be used as Internal Voltage Reference.

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 the ADCL and ADCH.

Bits 4:0 – MUXn: Analog Channel and Gain Selection Bits [n = 4:0]

The value of these bits selects which combination of analog inputs are connected to the ADC. These bits

also select the gain for the differential channels. 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).

Atmel ATmega644A [DATASHEET]

Atmel-42716C-ATmega644A_Datasheet_Complete-10/2016

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