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ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
Bit 5 – AREFEN: Analog Reference pin Enable
Set this bit to connect the internal AREF circuit to the AREF pin.
Clear this bit to disconnect the internal AREF circuit from the AREF pin.
Bit 4 – Res: Reserved
This bit is reserved and will always read as zero.
Bit 3:0– ADTS[3:0]: ADC Auto Trigger Source Selection Bits
These bits are only necessary in case the ADC works in auto trigger mode. It means if ADATE bit in ADCSRA reg-
ister is set.
In accordance with the
Table 21-7, these three bits select the interrupt event which will generate the trigger of the
start of conversion. The start of conversion will be generated by the rising edge of the selected interrupt flag
whether the interrupt is enabled or not. In case of trig on PSCnASY event, there is no flag. So in this case a conver-
sion will start each time the trig event appears and the previous conversion is completed.
21.10.5
ADCH and ADCL – ADC Result Data Registers
When an ADC conversion is complete, the conversion results are stored in these two result data registers.
When the ADCL register is read, the two ADC result data registers can’t be updated until the ADCH register has
also been read.
Consequently, in 10-bit configuration, the ADCL register must be read first before the ADCH.
Nevertheless, to work easily with only 8-bit precision, there is the possibility to left adjust the result thanks to the
ADLAR bit in the ADCSRA register. Like this, it is sufficient to only read ADCH to have the conversion result.
Table 21-7.
ADC auto trigger source selection.
ADTS[3:0]
Description
0000
Free Running mode
0001
External interrupt request 0
0010
Timer/Counter0 compare match
0011
Timer/Counter0 overflow
0100
Timer/Counter1 compare Match B
0101
Timer/Counter1 overflow
0110
Timer/Counter1 capture event
0111
PSC Module 0 synchronization signal
1000
PSC Module 1 synchronization signal
1001
PSC Module 2 synchronization signal
1010
Analog comparator 0
1011
Analog comparator 1
1100
Analog comparator 2
1101
Analog comparator 3
1110
Reserved
1111
Reserved