Datasheet

217
ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
21.6 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC result registers (ADCL,
ADCH).
For single ended conversion, the result is:
where V
IN
is the voltage on the selected input pin and V
REF
the selected voltage reference (see Table 21-2 and
Table 21-3 on page 218). 0x000 represents analog ground, and 0x3FF represents the selected reference voltage minus one
LSB.
21.6.1 ADC Multiplexer Selection Register – ADMUX
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 21-2. 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.
•
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 Section 21.6.3 “The ADC
Data Register – ADCL and ADCH” on page 219.
• Bit 4 – Res: Reserved Bit
This bit is an unused bit in the Atmel
®
ATmega48/88/168, and will always read as zero.
• Bits 3:0 – MUX3:0: Analog Channel Selection Bits
The value of these bits selects which analog inputs are connected to the ADC. See Table 21-3 on page 218 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).
ADC
V
IN
1024⋅
V
REF
-------------------------
=
Bit 76543210
REFS1 REFS0 ADLAR – MUX3 MUX2 MUX1 MUX0 ADMUX
Read/Write R/W R/W R/W R R/W R/W R/W R/W
Initial Value00000000
Table 21-2. Voltage Reference Selections for ADC
REFS1 REFS0 Voltage Reference Selection
0 0 AREF, Internal V
ref
turned off
0 1 AV
CC
with external capacitor at AREF pin
1 0 Reserved
1 1 Internal 1.1V Voltage Reference with external capacitor at AREF pin