ATtiny5 datasheet(86/168 Pages) ATMEL

86 / 168 page

8127C–AVR–10/09

ATtiny4/5/9/10

switched on by setting the ADEN bit in ADCSRA. The prescaler keeps running for as long as the

ADEN bit is set, and is continuously reset when ADEN is low.

When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion

starts at the following rising edge of the ADC clock cycle.

A normal conversion takes 13 ADC clock cycles, as summarised in Table 13-1 on page 87. The

first conversion after the ADC is switched on (ADEN in ADCSRA is set) takes 25 ADC clock

cycles in order to initialize the analog circuitry. See Figure 13-4.

Figure 13-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)

The actual sample-and-hold takes place 3 ADC clock cycles after the start of a normal conver-

sion and 16 ADC clock cycles after the start of a first conversion. See Figure 13-5. When a

conversion is complete, the result is written to the ADC Data Registers, and ADIF is set. In Sin-

gle Conversion mode, ADSC is cleared simultaneously. The software may then set ADSC again,

and a new conversion will be initiated on the first rising ADC clock edge.

Figure 13-5. ADC Timing Diagram, Single Conversion

When Auto Triggering is used, the prescaler is reset when the trigger event occurs. See Figure

13-6. This assures a fixed delay from the trigger event to the start of conversion. In this mode,

the sample-and-hold takes place two ADC clock cycles after the rising edge on the trigger

source signal. Three additional CPU clock cycles are used for synchronization logic.

Conversion Result

ADC Clock

ADSC

Sample & Hold

ADIF

ADCL

Cycle Number

ADEN

212

First Conversion

Conversion

MUX

Update

MUX

Update

Conversion

Complete

Conversion Result

ADC Clock

ADSC

ADIF

ADCL

Cycle Number

One Conversion

Next Conversion

Sample & Hold

MUX

Update

Conversion

Complete

MUX

Update

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