attiny24v ATMEL Corporation, attiny24v Datasheet - Page 145

• Manufacturer Part Number: attiny24v
• Description: 8-bit Avr Microcontroller With 2/4/8k Bytes Insystem Programmable Flash
• Manufacturer: ATMEL Corporation

16.13 Register Description
16.13.1
8006H–AVR–10/09
ADMUX – ADC Multiplexer Selection Register
• Bit 7:6 – REFS1:REFS0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in
Table 16-3.
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). Also note, that when these bits are changed,
the next conversion will take 25 ADC clock cycles.
Special care should be taken when changing differential channels. Once a differential channel
has been selected the input stage may take a while to stabilize. It is therefore recommended to
force the ADC to perform a long conversion when changing multiplexer or voltage reference set-
tings. This can be done by first turning off the ADC, then changing reference settings and then
turn on the ADC. Alternatively, the first conversion results after changing reference settings
should be discarded.
It is not recommended to use an external AREF higher than (V
ential gain, as this will affect ADC accuracy.
Internal voltage reference options may not be used if an external voltage is being applied to the
AREF pin.
• Bits 5:0 – MUX5:0: Analog Channel and Gain Selection Bits
The value of these bits selects which combination of analog inputs are connected to the ADC. In
case of differential input, gain selection is also made with these bits. Selections on
page 146
the offset calibration selections are located. Selecting the single-ended channel ADC8 enables
the temperature measurement. See
changed during a conversion, the change will not go into effect until this conversion is complete
(ADIF in ADCSRA is set).
Special care should be taken when changing differential channels. Once a differential channel
has been selected the input stage may take a while to stabilize. It is therefore recommended to
force the ADC to perform a long conversion when changing multiplexer settings. This can be
Bit
0x07 (0x27)
Read/Write
Initial Value
REFS1
0
0
1
1
show values for single endid channels and where the differential channels as well as
REFS0
Voltage Reference Selections for ADC
REFS1
0
1
0
1
R/W
7
0
Voltage Reference Selection
V
External voltage reference at PA0 (AREF) pin, internal reference turned off
Internal 1.1V voltage reference
Reserved
CC
REFS0
R/W
6
0
used as analog reference, disconnected from PA0 (AREF)
MUX5
R/W
5
0
Table 16-4 on page 146
MUX4
R/W
4
0
MUX3
R/W
3
0
MUX2
R/W
2
0
CC
Table
for details. If these bits are
- 1V) for channels with differ-
ATtiny24/44/84
MUX1
R/W
16-3.
1
0
MUX0
R/W
0
0
Table 16-4 on
ADMUX
145