Datasheet

In order to have an accurate sampling frequency control, there is the possibility to update the DAC input
values through different trigger events.
25.4. Starting a conversion
The DAC is configured thanks to the DACON register. As soon as the DAEN bit in DACON register is set,
the DAC converts the value present on the DACH and DACL registers in accordance with the register
DACON setting.
Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is enabled
by setting the DAC Auto Trigger Enable bit, DAATE in DACON. The trigger source is selected by setting
the DAC Trigger Select bits, DATS in DACON (See description of the DATS bits for a list of the trigger
sources). When a positive edge occurs on the selected trigger signal, the DAC converts the value present
on the DACH and DACL registers in accordance with the register DACON setting. This provides a
method of starting conversions at fixed intervals. If the trigger signal is still set when the conversion
completes, a new conversion will not be started. If another positive edge occurs on the trigger signal
during conversion, the edge will be ignored. Note that an interrupt flag will be set even if the specific
interrupt is disabled or the Global Interrupt Enable bit in SREG is cleared. A conversion can thus be
triggered without causing an interrupt. However, the interrupt flag must be cleared in order to trigger a
new conversion at the next interrupt event.
25.4.1. DAC voltage reference
The reference voltage for the ADC (V
REF
) indicates the conversion range for the DAC. V
REF
can be
selected as either AV
CC
, internal 2.56V reference, or external AREF pin.
AV
CC
is connected to the DAC through a passive switch. The internal 2.56V reference is generated from
the internal bandgap reference (V
BG
) through an internal amplifier. In either case, the external AREF pin
is directly connected to the DAC, and the reference voltage can be made more immune to noise by
connecting a capacitor between the AREF pin and ground. V
REF
can also be measured at the AREF pin
with a high impedance voltmeter. Note that V
REF
is a high impedance source, and only a capacitive load
should be connected in a system.
If the user has a fixed voltage source connected to the AREF pin, the user may not use the other
reference voltage options in the application, as they will be shorted to the external voltage. If no external
voltage is applied to the AREF pin, the user may switch between AV
CC
and 2.56V as reference selection.
The first DAC conversion result after switching reference voltage source may be inaccurate, and the user
is advised to discard this result.
25.5. Register Description
Atmel ATmega16M1/32M1/64M1 [DATASHEET]
Atmel-8209F-ATmega16M1/32M1/64M1_Datasheet_Complete-10/2016
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