387
8331B–AVR–03/12
Atmel AVR XMEGA AU
A DAC conversion is automatically started when new data to be converted are available. Events
from the event system can also be used to trigger a conversion, and this enables synchronized
and timed conversions between the DAC and other peripherals, such as a timer/counter. The
DMA controller can be used to transfer data to the DAC.
The DAC has high drive strength, and is capable of driving both resistive and capacitive loads,
aswell as loads which combine both. A low-power mode is available, which will reduce the drive
strength of the output.
Internal and external voltage references can be used. The DAC output is also internally available
for use as input to the analog comparator or ADC.
29.3
Voltage reference selection
The following can be used as the referencevoltage (VREF) for the DAC”
– AV
CC
voltage
– Accurate internal 1.00V voltage
– External voltage applied to AREF pin on PORTA
– External voltage applied to AREF pin on PORTB
29.4
Starting a Conversion
By default, conversions are started automatically when new data are written to the channel data
register. It is also possible to enable events from the event system to trigger conversion starts.
When enabled, a new conversion is started when the DAC channel receives an event and the
channel data register has been updated. This enables conversion starts to be synchronized with
external events and/or timed to ensure regular and fixed conversion intervals.
29.5
Output and output channels
The two DAC channels have fully independent outputs and individual data and conversion con-
trol registers. This enables the DAC to create two different analog signals. The channel 0 output
can also be made internally available as input for the Analog Comparator and the ADC.
The output voltage from a DAC channel (V
DAC
) is given as:
29.6
DAC Output model
Each DAC output channel has a driver buffer with feedback to ensure that the voltage on the
DAC output pin is equal to the DACs internal voltage.
shows the DAC
output model. For details on
R
channel
, refer to the DAC characteristics in the device data sheet.
V
DACn
CHnDATA
0
xFFF
----------------------------
VREF
×
=
