
231
2593O–AVR–02/12
ATmega644
20.3
Register Description
20.3.1
ADCSRB – ADC Control and Status Register B
Bit 6 – ACME: Analog Comparator Multiplexer Enable
When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the
ADC multiplexer selects the negative input to the Analog Comparator. When this bit is written
logic zero, AIN1 is applied to the negative input of the Analog Comparator. For a detailed
20.3.2
ACSR – Analog Comparator Control and Status Register
Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the Analog Comparator is switched off. This bit
can be set at any time to turn off the Analog Comparator. This will reduce power consumption in
Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be
disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the bit is
changed.
Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set, a fixed bandgap reference voltage replaces the positive input to the Analog
Comparator. When this bit is cleared, AIN0 is applied to the positive input of the Analog Compar-
ator. When the bandgap reference voltage is used as input to the Analog Comparator, it will take
a certain time for the voltage to stabilize. If not stabilized, the first conversion may give a wrong
Bit 5 – ACO: Analog Comparator Output
10
010
ADC2
10
011
ADC3
10
100
ADC4
10
101
ADC5
10
110
ADC6
10
111
ADC7
Table 20-1.
Analog Comparator Mulitiplexed Input
ACME
ADEN
MUX2..0
Analog Comparator Negative Input
Bit
7
65
432
10
–
ACME
–
MUX5
ADTS2
ADTS1
ADTS0
ADCSRB
Read/Write
R
R/W
R
R/W
Initial Value
0
Bit
76543210
ACD
ACBG
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
ACSR
Read/Write
R/W
R
R/W
Initial Value
0
N/A
00000