Rainbow Electronics ATtiny26L - Manual (Page 84)

84
ATtiny26(L)
1477B–AVR–04/02
ADC Multiplexer Selection
Register – ADMUX
• Bit 7, 6 – REFS1, REFS0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in Table 36. If these bits
are changed during a conversion, the change will not go in effect until this conversion is
complete (ADIF in ADCSR is set). The user should disregard the first conversion result
after changing these bits to obtain maximum accuracy. If differential channels are used,
using AVCC or an external AREF higher than (AVCC - 0.2V) is not recommended, as
this will affect ADC accuracy. The internal voltage reference 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. If ADLAR is cleared, the result is right adjusted. If ADLAR is set, the result is
left 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 “ADC
Data Register – ADCL and ADCH” on page 87.
• Bits 4..0 – MUX4..MUX0: Analog Channel and Gain Selection Bits
The value of these bits selects which combination of analog inputs are connected to the
ADC. These bits also select the gain for the differential channels. See Table 37 for
details.
If these bits are changed during a conversion, the change will not go in effect
until this conversion is complete (ADIF in ADCSR is set).
Bit 7 6 5 4 3 2 1 0
$07 ($27) REFS1 REFS0 ADLAR MUX4 MUX3 MUX2 MUX1 MUX0 ADMUX
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 36. Voltage Reference Selections for ADC
REFS1 REFS0 Voltage Reference Selection
0 0 AVCC
0 1 AREF (PA3), Internal Vref turned off.
1 0 Internal Voltage Reference (2.56 V), AREF pin (PA3) not connected.
1 1
Internal Voltage Reference (2.56 V) with external capacitor at AREF pin
(PA3).