
450
42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
After the channel or reference voltage selection is updated a settling time is required for
the ADC and the gain amplifier or the reference voltage to stabilize. When changing
the channel selection while the ADC is enabled the required settling phase is
For consideration on changing the reference voltage selection please refer to section
27.6.1 Accessing the ADMUX Register
The channel selection bits MUX4:0 and MUX5 are located in two different register, the
ADMUX and the ADCSRB register. To ensure that changes go only into effect after
access to the MUX4:0 bits which triggers the update of the internal buffer. If only the
MUX4:0 bits need to be modified then a write access to the MUX4:0 bits is sufficient.
27.6.2 ADC Input Channels
The ADC input channels can be changed while the ADC is running under the condition
that the previous channel was a single-ended one. Changing between differential
channels however requires that the ADC is disabled and enabled again to make the
ADC go through the initial start-up phase.
If changing from single-ended to single-ended or from single-ended to differential input
channels a settling phase is automatically inserted by the ADC interface logic after the
input channel is modified. The settling phase is required by the ADC and the gain
amplifier to stabilize. If a conversions start is requested during this settling phase, by
setting ADSC or by a trigger event in Auto Triggered mode then the conversion is
started only after the settling phase has completed.
Figure 27-9. ADC Timing Diagram, Changing MUXn after a Conversion
A D C C lo c k
A D IF
A D C H
A D C L
tA S ET
A D C S e ttlin g
C o n v e rs io n
S ig n a n d M S B o f R e s u lt
L S B o f R e s u lt
C o n v e rs io n
C o m p le te
M U X 5 :0
M U X 5 :0 internal
O ld C h a n n e l
N e w C h a n n e l
O ld C h a n n e l
A D C In p u t
C h a n n e l is
c h a n g e d
tC H D LY
N e w C o n v e rs io n
c a n b e s ta rte d
fro m h e re
In case the MUXn bits are altered during an ongoing conversion, the ADC input channel
is changed after the conversion has completed. MUXn changes occurring during the
tracking phase, which follows a conversion, will stop the tracking phase and the ADC
settling phase will be entered.