ATtiny43U datasheet(120/182 Pages) ATMEL

120 / 182 page

120

8048B–AVR–03/09

ATtiny43U

Figure 16-7. ADC Timing Diagram, Free Running Conversion

For a summary of conversion times, see Table 16-1.

16.6

Changing Channel or Reference Selection

The MUX[2:0] and REFS bits in the ADMUX Register are single buffered through a temporary

selection only takes place at a safe point during the conversion. The channel and reference

selection is continuously updated until a conversion is started. Once the conversion starts, the

channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Con-

tinuous updating resumes in the last ADC clock cycle before the conversion completes (ADIF in

ADCSRA is set). Note that the conversion starts on the following rising ADC clock edge after

ADSC is written. The user is thus advised not to write new channel or reference selection values

to ADMUX until one ADC clock cycle after ADSC is written.

If Auto Triggering is used, the exact time of the triggering event can be indeterministic. Special

care must be taken when updating the ADMUX Register, in order to control which conversion

will be affected by the new settings.

Table 16-1.

ADC Conversion Time

Condition

Sample & Hold (Cycles from

Start of Conversion)

Conversion Time (Cycles)

First conversion

13.5

Normal conversions

1.5

Auto Triggered conversions

13.5

Free Running conversion

2.5

Sign and MSB of Result

LSB of Result

ADC Clock

ADSC

ADIF

ADCH

ADCL

Cycle Number

One Conversion

Next Conversion

Conversion

Complete

Sample & Hold

MUX and REFS

Update

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