ATmega16 datasheet(201/315 Pages) ATMEL

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ATmega16(L)

2466E–AVR–10/02

Figure 99. 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 Run-

ning 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. 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 to one. ADSC can also be used to determine if a conversion is in progress.

The ADSC bit will be read as one during a conversion, independently of how the conver-

sion was started.

Prescaling and

Conversion Timing

Figure 100. ADC Prescaler

By default, the successive approximation circuitry requires an input clock frequency

between 50 kHz and 200 kHz to get maximum resolution. If a lower resolution than 10

bits is needed, the input clock frequency to the ADC can be higher than 200 kHz to get a

higher sample rate. Alternatively, setting the ADHSM bit in SFIOR allows an increased

ADC clock frequency at the expense of higher power consumption.

The ADC module contains a prescaler, which generates an acceptable ADC clock fre-

quency from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits

in ADCSRA. The prescaler starts counting from the moment the ADC is switched on by

ADSC

ADIF

SOURCE 1

SOURCE n

ADTS[2:0]

CONVERSION

LOGIC

PRESCALER

START

CLK

ADC

EDGE

DETECTOR

ADATE

7-BIT ADC PRESCALER

ADC CLOCK SOURCE

ADPS0

ADPS1

ADPS2

Reset

ADEN

START

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