ATMEGA8-16AI SL383 Atmel, ATMEGA8-16AI SL383 Datasheet - Page 200

• Manufacturer Part Number: ATMEGA8-16AI SL383
• Description: Semiconductors and Actives, Microprocessors, Microcontrollers
• Manufacturer: Atmel

Changing Channel
or Reference
Selection
200
ATmega8(L)
Figure 94. ADC Timing Diagram, Free Running Conversion
Table 73. ADC Conversion Time
The MUXn and REFS1:0 bits in the ADMUX Register are single buffered through a temporary
register to which the CPU has random access. This ensures that the channels and reference
selection only takes place at a safe point during the conversion. The channel and reference
selection is continuously updated until a conversion is started. Once the conversion starts, the
channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Con-
tinuous updating resumes in the last ADC clock cycle before the conversion completes (ADIF in
ADCSRA is set). Note that the conversion starts on the following rising ADC clock edge after
ADSC is written. The user is thus advised not to write new channel or reference selection values
to ADMUX until one ADC clock cycle after ADSC is written.
If both ADFR and ADEN is written to one, an interrupt event can occur at any time. If the
ADMUX Register is changed in this period, the user cannot tell if the next conversion is based
on the old or the new settings. ADMUX can be safely updated in the following ways:
1. When ADFR or ADEN is cleared.
2. During conversion, minimum one ADC clock cycle after the trigger event.
3. After a conversion, before the Interrupt Flag used as trigger source is cleared.
When updating ADMUX in one of these conditions, the new settings will affect the next ADC
conversion.
Condition
Extended conversion
Normal conversions, single ended
Cycle Number
ADC Clock
ADSC
ADIF
ADCH
ADCL
Conversion
Complete
One Conversion
from Start of Conversion)
11
Sample & Hold (Cycles
12
13
13.5
1.5
Next Conversion
1
MSB of Result
LSB of Result
2
MUX and REFS
Update
3
Sample &Hold
4
Conversion Time
(Cycles)
25
13
2486W–AVR–02/10