ATtiny167-ESSZ datasheet(194/282 Pages) ATMEL

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194

7728D–AVR–07/09

ATtiny87/ATtiny167

17.4

Starting a Conversion

A single conversion is started by writing a logical one to the ADC Start Conversion bit, ADSC.

This bit stays high as long as the conversion is in progress and will be cleared by hardware

when the conversion is completed. If a different data channel is selected while a conversion is

in progress, the ADC will finish the current conversion before performing the channel change.

Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering

is enabled by setting the ADC Auto Trigger Enable bit, ADATE in ADCSRA register. The trig-

ger source is selected by setting the ADC Trigger Select bits, ADTS in ADCSRB register (see

description of the ADTS bits for a list of the trigger sources). When a positive edge occurs on

the selected trigger signal, the ADC prescaler is reset and a conversion is started. This pro-

vides a method of starting conversions at fixed intervals. If the trigger signal still is 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 register 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.

Figure 17-2. ADC Auto Trigger Logic

Using the ADC Interrupt Flag as a trigger source makes the ADC start a new conversion as

soon as the ongoing conversion has finished. The ADC then operates in Free Running mode,

constantly sampling and updating the ADC Data Register. The first conversion must be started

by writing a logical one to the ADSC bit in ADCSRA register. In this mode the ADC will perform

successive conversions independently of whether the ADC Interrupt Flag, ADIF is cleared or

not.

If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA

bit will be read as one during a conversion, independently of how the conversion was started.

ADSC

ADIF

SOURCE 1

SOURCE n

ADTS[2:0]

Conversion

Logic

ADC Prescaler

Start

CLK

ADC

CLK

. . .

Edge

Detector

ADATE

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