ATMEGA169V Datasheet, PDF (205/365 Pages) ATMEL Corporation – 8-bit Microcontroller with 16K Bytes In-System Programmable Flash

ATmega169/V
ADC Multiplexer Selection
Register – ADMUX
Table 88. Correlation Between Input Voltage and Output Codes
V_ADCn
V_ADCm + V_REF
V_ADCm + ⁵¹¹/₅₁₂ V_REF
V_ADCm + ⁵¹⁰/₅₁₂ V_REF
...
V_ADCm + ¹/₅₁₂ V_REF
V_ADCm
V_ADCm - ¹/₅₁₂ V_REF
...
V_ADCm - ⁵¹¹/₅₁₂ V_REF
V_ADCm - V_REF
Read Code
0x1FF
0x1FF
0x1FE
...
0x001
0x000
0x3FF
...
0x201
0x200
Corresponding Decimal Value
511
511
510
...
1
0
-1
...
-511
-512
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
Read/Write
Initial Value
7
REFS1
R/W
0
6
REFS0
R/W
0
5
ADLAR
R/W
0
4
MUX4
R/W
0
3
MUX3
R/W
0
2
MUX2
R/W
0
1
MUX1
R/W
0
0
MUX0
R/W
0
ADMUX
• 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
REFS1 REFS0 Voltage Reference Selection
0
0
AREF, Internal Vref turned off
0
1
AVCC with external capacitor at AREF pin
1
0
Reserved
1
1
Internal 1.1V Voltage Reference with external capacitor at AREF pin
• 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.
2514P–AVR–07/06
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