ATmega1281R231 Atmel Corporation, ATmega1281R231 Datasheet - Page 289

• Manufacturer Part Number: ATmega1281R231
• Manufacturer: Atmel Corporation

Specifications of ATmega1281R231

• Flash (kbytes): 128 Kbytes
• Max. Operating Frequency: 16 MHz
• Max I/o Pins: 54
• Spi: 3
• Twi (i2c): 1
• Uart: 2
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Crypto Engine: AES
• Sram (kbytes): 8
• Eeprom (bytes): 4096
• Operating Voltage (vcc): 1.8 to 3.6
• Timers: 6
• Frequency Band: 2.4 GHz
• Max Data Rate (mb/s): 2
• Antenna Diversity: Yes
• External Pa Control: Yes
• Power Output (dbm): 3
• Receiver Sensitivity (dbm): -101
• Receive Current Consumption (ma): 13.2
• Transmit Current Consumption (ma): 14.4
• Link Budget (dbm): 104

26.8
26.8.1
2549N–AVR–05/11
Register Description
ADMUX – ADC Multiplexer Selection Register
Table 26-2.
Example:
ADMUX = 0xFB (ADC3 - ADC2, 10× gain, 2.56V reference, left adjusted result).
Voltage on ADC3 is 300mV, voltage on ADC2 is 500mV.
ADCR = 512 × 10 × (300 - 500) / 2560 = -400 = 0x270.
ADCL will thus read 0x00, and ADCH will read 0x9C. Writing zero to ADLAR right adjusts the
result: ADCL = 0x70, ADCH = 0x02.
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in
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 26-3.
Note:
Bit
(0x7C)
Read/Write
Initial Value
V
V
V
...
V
V
V
...
V
V
V
ADCn
ADCm
ADCm
ADCm
ADCm
ADCm
ADCm
ADCm
REFS1
ADCm
0
0
1
1
+ 0.999 V
+ 0.998 V
+ 0.001 V
- 0.001 V
- 0.999 V
- V
+ V
1. If 10x or 200x gain is selected, only 2.56V should be used as Internal Voltage Reference. For
REF
REF
differential conversion, only 1.1V cannot be used as internal voltage reference.
/ GAIN
/ GAIN
Correlation Between Input Voltage and Output Codes
Voltage Reference Selections for ADC
REFS0
REFS1
REF
REF
REF
REF
REF
R/W
7
0
0
1
0
1
/ GAIN
/ GAIN
/ GAIN
/ GAIN
/ GAIN
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
ATmega640/1280/1281/2560/2561
ADLAR
R/W
Read Code
0x1FF
0x1FF
0x1FE
...
0x001
0x000
0x3FF
...
0x201
0x200
5
0
REF
MUX4
R/W
turned off
4
0
MUX3
R/W
(1)
3
0
MUX2
R/W
Corresponding Decimal Value
2
0
Table
MUX1
R/W
1
0
26-3. If these bits are
-511
-512
511
511
510
...
-1
...
1
0
MUX0
R/W
0
0
ADMUX
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