357
8331B–AVR–03/12
Atmel AVR XMEGA AU
The ADC has a compare function for accurate monitoring of user defined thresholds with mini-
mum software intervention required.
Figure 28-1.
ADC overview.
28.3
Input Sources
Input sources are the voltage inputs that the ADC can measure and convert. Four types of mea-
surements can be selected:
• Differential input
• Differential input with gain
• Single-ended input
• Internal input
The input pins are used for single-ended and differential input, while the internal inputs are
directly available inside the device. In devices with two ADCs, PORTA pins can be input to
ADCA and PORTB pins can be input to ADCB. For AVR XMEGA devices with only one ADC,
input pins may be available for ADCA on both PORTA and PORTB.
The ADC is differential, and so for single-ended measurements the negative input is connected
to a fixed internal value. The four types of measurements and their corresponding input options
are shown in
28.3.1
Differential Input
When differential input is enabled, all input pins can be selected as positive input, and input pins
0 to 3 can be selected as negative input. The ADC must be in signed mode when differential
input is used.
Internal 1.00V
Internal VCC/1.6V
AREFA
AREFB
S&H
Σ
ADC
DAC
2x
2 bits
V
IN
V
OUT
Stage
1
Stage
2
Stage
12
Digital Correction Logic
2
2
2
Internal VCC/2
CHn.CTRL
REFCTRL
CHn.MUXCTRL
EVCTRL
CTRLA
CTRLB
Enable
Start
Mode
Resolution
Action
Select
CH1 Result
CH0 Result
CH2 Result
Compare
<
>
Threshold
(Int Req)
CH3 Result
V
INP
V
INN
Internal
signals
Internal
signals
ADC0
ADC7
ADC4
ADC7
ADC0
ADC3
•
•
•
Int. signals
Int. signals
½x - 64x
•
•
•
•
•
•
ADC0
ADC15
•
•
•
