ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 243

• Manufacturer Part Number: ATMEga64L
• Description: 8-bit AVR Microcontroller with 64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

ADC Multiplexer Selection
Register – ADMUX
2490G–AVR–03/04
Table 96. Correlation Between Input Voltage and Output Codes
Example:
ADMUX = 0xED (ADC3 - ADC2, 10x gain, 2.56V reference, left adjusted result).
Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.
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 Table 97. 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 97. Voltage Reference Selections for ADC
Bit
Read/Write
Initial Value
V
V
V
...
V
V
V
...
V
V
REFS1
V
ADCn
ADCm
ADCm
ADCm
ADCm
ADCm
ADCm
ADCm
ADCm
0
0
1
1
+ 0.999 V
+ 0.998 V
+ 0.001 V
- 0.001 V
- 0.999 V
- V
+ V
REF
REF
REFS0
/GAIN
/GAIN
REFS1
0
1
0
1
R/W
REF
REF
7
0
REF
REF
REF
/GAIN
/GAIN
/GAIN
/GAIN
/GAIN
Voltage Reference Selection
AREF, Internal Vref turned off.
AVCC with external capacitor at AREF pin.
Reserved
Internal 2.56V Voltage Reference with external capacitor at AREF pin.
REFS0
R/W
6
0
ADLAR
R/W
5
0
Read Code
0x1FF
0x1FF
0x1FE
...
0x001
0x000
0x3FF
...
0x201
0x200
MUX4
R/W
4
0
MUX3
R/W
3
0
Corresponding Decimal Value
MUX2
R/W
2
0
ATmega64(L)
MUX1
R/W
1
0
-511
-512
511
511
510
-1
...
...
1
0
MUX0
R/W
0
0
ADMUX
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