ATA5771_09 ATMEL [ATMEL Corporation], ATA5771_09 Datasheet - Page 194

• Manufacturer Part Number: ATA5771_09
• Description: Microcontroller with UHF ASK/FSK Transmitter
• Manufacturer: ATMEL [ATMEL Corporation]

18.5
7701C–AVR–12/08
Prescaling and Conversion Timing
Figure 18-2. 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, con-
stantly 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 conversion was started.
Figure 18-3. 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.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency
from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits in ADCSRA.
ADSC
SOURCE n
ADIF
SOURCE 1
.
.
.
.
START
ADEN
ADTS[2:0]
ADPS0
ADPS1
ADPS2
CK
DETECTOR
EDGE
Reset
ADATE
7-BIT ADC PRESCALER
ADC CLOCK SOURCE
START
ATtiny24/44/84
CONVERSION
PRESCALER
LOGIC
CLK
ADC
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