AT90PWM2 datasheet(268/365 Pages) ATMEL

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268

AT90PWM2/3

4317B–AVR–02/05

Operation

The Digital to Analog Converter generates an analog signal proportional to the value of

the DAC registers value.

In order to have an accurate sampling frequency control, there is the possibility to

update the DAC input values through different trigger events.

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 Trig-

gering 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 conver-

sion at the next interrupt event.

DAC Voltage Reference

The reference voltage for the ADC (V

REF) indicates the conversion range for the DAC.

REF can be selected as either AVCC, internal 2.56V reference, or external AREF pin.

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 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 dis-

card this result.

AT90PWM2 Datasheet(PDF) 268 Page - ATMEL Corporation

AT90PWM2 Datasheet(HTML) 268 Page - ATMEL Corporation

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