attiny25v ATMEL Corporation, attiny25v Datasheet - Page 129

• Manufacturer Part Number: attiny25v
• Description: Microcontroller With 2/4/8k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

17.5
2586K–AVR–01/08
Prescaling and Conversion Timing
Figure 17-2. ADC Auto Trigger Logic
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 17-3. 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. It is
not recommended to use a higher input clock frequency than 1 MHz.
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.
The prescaler starts counting from the moment the ADC is 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.
ADSC
SOURCE n
ADIF
SOURCE 1
.
.
.
.
ADEN
START
ADTS[2:0]
ADPS0
ADPS1
ADPS2
CK
DETECTOR
EDGE
Reset
ADATE
7-BIT ADC PRESCALER
ADC CLOCK SOURCE
START
ATtiny25/45/85
CONVERSION
PRESCALER
LOGIC
CLK
ADC
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