AT90PWM2 datasheet(260/361 Pages) ATMEL

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260

4317J–AVR–08/10

AT90PWM2/3/2B/3B

rupt 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.

22.3.1

DAC Voltage Reference

The reference voltage for the ADC (V

REF) indicates the conversion range for the DAC. VREF can

be selected as either AV

CC, internal 2.56V reference, or external AREF pin.

CC is connected to the DAC through a passive switch. The internal 2.56V reference is gener-

ated 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 impedant voltmeter. Note that V

REF is a high

impedant 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.

22.4

DAC Register Description

The DAC is controlled via three dedicated registers:

•

The DACON register which is used for DAC configuration

•

DACH and DACL which are used to set the value to be converted.

22.4.1

Digital to Analog Conversion Control Register – DACON

• Bit 7 – DAATE: DAC Auto Trigger Enable bit

Set this bit to update the DAC input value on the positive edge of the trigger signal selected with

the DACTS2-0 bit in DACON register.

Clear it to automatically update the DAC input when a value is written on DACH register.

• Bit 6:4 – DATS2, DATS1, DATS0: DAC Trigger Selection bits

These bits are only necessary in case the DAC works in auto trigger mode. It means if DAATE

bit is set.

In accordance with the Table 22-1, these 3 bits select the interrupt event which will generate the

update of the DAC input values. The update will be generated by the rising edge of the selected

interrupt flag whether the interrupt is enabled or not.

Bit

654

DAATE

DATS2

DATS1

DATS0

DALA

DAOE

DAEN

DACON

Read/Write

R/W

Initial Value

Table 22-1.

DAC Auto Trigger source selection

DATS2

DATS1

DATS0

Description

Analog comparator 0

Analog comparator 1

External Interrupt Request 0

Timer/Counter0 Compare Match

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