ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 141

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

7701E–AVR–02/11
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.
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. The first conversion after the ADC is
switched on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize the ana-
log circuitry.
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal con-
version and 14.5 ADC clock cycles after the start of a first conversion. When a conversion is
complete, the result is written to the ADC data registers, and ADIF is set. In single-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.
When auto triggering is used, the prescaler is reset when the trigger event occurs. This
assures a fixed delay from the trigger event to the start of conversion. In this mode, the sam-
ple-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.
In free running mode, a new conversion will be started immediately after the conversion com-
pletes, while ADSC remains high. For a summary of conversion times, see
page
Figure 18-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)
Figure 18-5. ADC Timing Diagram, Single Conversion
Cycle Number
ADC Clock
ADSC
ADIF
ADCH
ADCL
Cycle Number
ADC Clock
ADEN
ADSC
ADIF
ADCH
ADCL
142.
1
1
2
MUX and REFS
Update
2
MUX and REFS
Update
12
Atmel ATtiny24/44/84 [Preliminary]
3
13
Sample & Hold
4
14
5
15
6
Sample & Hold
16
First Conversion
17
7
One Conversion
18
8
19
9
20
10
Conversion
Complete
21
11
22
Conversion
Complete
23
12
24
13
25
Sign and MSB of Result
Sign and MSB of Result
LSB of Result
Next Conversion
1
Next
Conversion
1
LSB of Result
Table 18-1 on
2
2
MUX and REFS
Update
MUX and REFS
Update
3
3
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