ATMEGA169 ATMEL [ATMEL Corporation], ATMEGA169 Datasheet - Page 205

• Manufacturer Part Number: ATMEGA169
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

ADC Multiplexer Selection
Register – ADMUX
2514P–AVR–07/06
Table 88. Correlation Between Input Voltage and Output Codes
ADMUX = 0xFB (ADC3 - ADC2, 1.1V reference, left adjusted result)
Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.
ADCR = 512 * (300 - 500) / 1100 = -93 = 0x3A3.
ADCL will thus read 0xC0, and ADCH will read 0xD8. Writing zero to ADLAR right
adjusts the result: ADCL = 0xA3, ADCH = 0x03.
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 89. 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 89. 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.
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
+
+
+
-
-
- V
+ V
1
511
511
510
1
/
/
512
REF
512
/
REF
REFS0
/
/
512
512
512
V
V
REFS1
0
1
0
1
REF
V
REF
R/W
V
V
REF
7
0
REF
REF
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
Read Code
0x1FF
0x1FF
0x1FE
...
0x001
0x000
0x3FF
...
0x201
0x200
ADLAR
R/W
5
0
MUX4
R/W
4
0
MUX3
R/W
3
0
Corresponding Decimal Value
MUX2
R/W
2
0
ATmega169/V
MUX1
R/W
-511
-512
511
511
510
1
0
...
-1
...
1
0
MUX0
R/W
0
0
ADMUX
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