ATMEGA2561V ATMEL [ATMEL Corporation], ATMEGA2561V Datasheet - Page 294

• Manufacturer Part Number: ATMEGA2561V
• Description: 8-bit Microcontroller with 64K/128K/256K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Register Description
ADMUX – ADC Multiplexer
Selection Register
294
ATmega640/1280/1281/2560/2561
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 128. 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 128. Voltage Reference Selections for ADC
Note:
• 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 – The ADC Data Register” on page 298.
• Bits 4:0 – MUX4:0: Analog Channel and Gain Selection Bits
The value of these bits selects which combination of analog inputs are connected to the
ADC. See Table 129 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
(0x7C)
Read/Write
Initial Value
REFS1
0
0
1
1
1. If 10x or 200x gain is selected, only 2.56 V should be used as Internal Voltage Refer-
ence. For differential conversion, only 1.1V cannot be used as internal voltage
reference.
REFS0
REFS1
R/W
7
0
0
1
0
1
REFS0
R/W
Voltage Reference Selection
AREF, Internal V
AVCC with external capacitor at AREF pin
Internal 1.1V Voltage Reference with external capacitor at AREF pin
Internal 2.56V Voltage Reference with external capacitor at AREF pin
6
0
ADLAR
R/W
5
0
REF
MUX4
R/W
4
0
turned off
MUX3
R/W
3
0
(1)
MUX2
R/W
2
0
MUX1
R/W
1
0
MUX0
R/W
0
0
2549K–AVR–01/07
ADMUX