74
ATmega103(L)
0945G–09/01
keeps running for as long as the ADEN bit is set and is continuously reset when ADEN
is low.
When initiating a conversion by setting the ADSC bit in ADCSR, the conversion starts at
the following falling edge of the ADC clock cycle. The actual sample-and-hold takes
place one ADC clock cycle after the start of the conversion. The result is ready and writ-
ten to the ADC Result Register after 13 cycles. The ADC needs two more clock cycles
before a new conversion can be started. If ADSC is set high in this period, the ADC will
start the new conversion immediately. For a summary of conversion times, see Table
26.
Figure 47.
ADC Timing Diagram, First Conversion
Figure 48.
ADC Timing Diagram
Table 26.
ADC Conversion Time
Condition
Sample
Cycle
Number
Result Ready
(Cycle
Number)
Total
Conversion
Time (Cycles)
Total
Conversion
Time (µs)
1st Conversion
14
26
28
140 - 560
Single Conversion
1
13
15
75 - 300
MSB of result
LSB of result
ADC clock
ADSC
Hold strobe
ADIF
ADCH
ADCL
Cycle number
ADEN
1
2
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
1
2
Dummy Conversion
Actual Conversion
Second
Conversion
1
2
3
4
5
6
7
8
9
10
11
12
13
MSB of result
LSB of result
ADC clock
ADSC
Hold strobe
ADIF
ADCH
ADCL
Cycle number
14
15
1
2
One Conversion
Next Conversion