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7647H–AVR–03/12
Atmel ATmega16/32/64/M1/C1
• Bit 6 – ISRCEN: Current Source Enable
Set this bit to source a 100µA current to the AREF pin.
Clear this bit to use AREF pin as Analog Reference pin.
• 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 Bit
This bit is unused bit in the ATmega16/32/64/M1/C1, and will always read as zero.
• Bit 3, 2, 1, 0– ADTS3:ADTS0: 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 register is set.
In accordance with the Table 18-7, these 3 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 conversion will start each time the trig event appears
and the previous conversion is completed..
Table 18-7. ADC Auto Trigger Source Selection
ADTS3 ADTS2 ADTS1 ADTS0 Description
0000Free Running Mode
0 0 0 1 External Interrupt Request 0
0 0 1 0 Timer/Counter0 Compare Match
0 0 1 1 Timer/Counter0 Overflow
0 1 0 0 Timer/Counter1 Compare Match B
0 1 0 1 Timer/Counter1 Overflow
0 1 1 0 Timer/Counter1 Capture Event
0 1 1 1 PSC Module 0 Synchronization Signal
1 0 0 0 PSC Module 1 Synchronization Signal
1 0 0 1 PSC Module 2 Synchronization Signal
1 0 1 0 Analog comparator 0
1 0 1 1 Analog comparator 1
1 1 0 0 Analog comparator 2
1 1 0 1 Analog comparator 3
1110Reserved
1111Reserved
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