ATMEGA325-16AJ ATMEL [ATMEL Corporation], ATMEGA325-16AJ Datasheet - Page 205

• Manufacturer Part Number: ATMEGA325-16AJ
• Description: 8-bit Microcontroller with In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

ADC Multiplexer Selection
Register – ADMUX
2570A–AVR–09/04
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 87. 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 87. Voltage Reference Selections for ADC
• 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
ADC Data Register – ADCL and ADCH” on page 208.
• Bits 4:0 – MUX4:0: Analog Channel Selection Bits
The value of these bits selects which combination of analog inputs are connected to the
ADC. See Table 88 for details. 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).
Bit
Read/Write
Initial Value
REFS1
0
0
1
1
REFS0
REFS1
0
1
0
1
R/W
7
0
Voltage Reference Selection
AREF, Internal Vref turned off
AVCC with external capacitor at AREF pin
Reserved
Internal 1.1V Voltage Reference with external capacitor at AREF pin
REFS0
R/W
6
0
ADLAR
R/W
5
0
ATmega325/3250/645/6450
MUX4
R/W
4
0
MUX3
R/W
3
0
MUX2
R/W
2
0
MUX1
R/W
1
0
MUX0
R/W
0
0
ADMUX
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