ATA8741 ATMEL Corporation, ATA8741 Datasheet - Page 166

• Manufacturer Part Number: ATA8741
• Manufacturer: ATMEL Corporation

25.10 Register Description
25.10.1
166
ATA8741
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
these bits are changed during a conversion, the change will not go in effect until this conversion
is complete (ADIF in ADCSR is set).
Special care should be taken when changing differential channels. Once a differential channel
has been selected, the stage may take as much as 25 ADC clock cycles to stabilize to the new
value. Thus conversions should not be started within the first 13 clock cycles after selecting a
new differential channel. Alternatively, conversion results obtained within this period should be
discarded.
The same settling time should be observed for the first differential conversion after changing
ADC reference (by changing the REFS1:0 bits in ADMUX).
If channels where differential gain is used ie. the gainstage, using V
AREF higher than (V
allowed to connect internal voltage reference to AREF pin, if an external voltage is being applied
to it already. Internal voltage reference is connected AREF pin when REFS1:0 is set to value
‘11’.
Table 25-3.
• 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
on page 167
well as 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).
Bit
0x07 (0x27)
Read/Write
Initial Value
REFS1
0
0
1
1
show values for single endid channels and where the the differential channels as
Voltage Reference Selections for ADC
REFS0
REFS1
R/W
7
0
0
1
0
1
CC
REFS0
- 1V) is not recommended, as this will affect ADC accuracy. It is not
R/W
Voltage Reference Selection
V
External Voltage Reference at PA0 (AREF) pin, Internal Voltage Reference
turned off.
Internal 1.1V Voltage Reference.
Reserved.
6
0
CC
used as analog reference, disconnected from PA0 (AREF).
MUX5
R/W
5
0
MUX4
R/W
4
0
Table 25-4 on page 167
MUX3
R/W
3
0
MUX2
R/W
2
0
Table 25-3 on page
for details. If these bits are
MUX1
CC
R/W
1
0
or an optional external
MUX0
R/W
9140B–INDCO–07/09
0
0
Table 25-4
ADMUX
166. If