Rainbow Electronics ATtiny43U - Manual (Page 118)

118
8048B–AVR–03/09
ATtiny43U
Figure 16-3. ADC Prescaler
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 16-1 on page 120 . 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, as shown in
Figure 16-4 below.
Figure 16-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conver-
sion and 13.5 ADC clock cycles after the start of a first conversion. See
Figure 16-5 . 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.
7-BIT ADC PRESCALER
ADC CLOCK SOURCE
CK
ADPS0
ADPS1
ADPS2
CK/128 CK/2 CK/4 CK/8 CK/16 CK/32 CK/64
Reset
ADEN
START
Sign and MSB of Result
LSB of Result
ADC Clock
ADSC
Sample & Hold
ADIF
ADCH
ADCL
Cycle Number
ADEN
1 2 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1 2
First Conversion
Next
Conversion
3
MUX and REFS
Update MUX and REFS
Update Conversion
Complete