ATtiny261-ESSZ datasheet(157/227 Pages) ATMEL

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157

7753C–AVR–07/09

ATtiny261/ATtiny461/ATtiny861

19.10 Register Description

19.10.1

ADMUX – ADC Multiplexer Selection Register

• Bit 7:6 – REFS1:REFS0: Voltage Reference Selection Bits

These bits and the REFS2 bit from the ADC Control and Status Register B (ADCSRB) select the

voltage reference for the ADC, as shown in Table 19-4. If these bits are changed during a

conversion, the change will not go in effect until this conversion is complete (ADIF in ADCSR is

set). Whenever these bits are changed, the next conversion will take 25 ADC clock cycles. If

active channels are used, using AVCC or an external AREF higher than (AVCC - 1V) is not

recommended, as this will affect ADC accuracy. The internal voltage reference options may not

be used if an external voltage is being applied to the 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 conver-

sions. For a complete description of this bit, see “ADCL and ADCH – The ADC Data Register” on

page 161.

• Bits 4:0 – MUX4:0: Analog Channel and Gain Selection Bits

These bits and the MUX5 bit from the ADC Control and Status Register B (ADCSRB) select

which combination of analog inputs are connected to the ADC. In case of differential input, gain

selection is also made with these bits. Selecting the same pin as both inputs to the differential

gain stage enables offset measurements. Selecting the single-ended channel ADC11 enables

the temperature sensor. Refer to Table 19-5 for details. 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).

Bit

65432

0x07 (0x27)

REFS1

REFS0

ADLAR

MUX4

MUX3

MUX2

MUX1

MUX0

ADMUX

Read/Write

R/W

Initial Value

00000

Table 19-4.

Voltage Reference Selections for ADC

REFS2

REFS1

REFS0

Voltage Reference (V

REF) Selection

CC used as Voltage Reference, disconnected from AREF.

External Voltage Reference at AREF pin, Internal Voltage

Reference turned off.

Internal 1.1V Voltage Reference.

Reserved.

Internal 2.56V Voltage Reference without external bypass

capacitor, disconnected from AREF.

Internal 2.56V Voltage Reference with external bypass capacitor

at AREF pin.

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