ATMEGA644_0702 Datasheet, PDF (230/374 Pages) ATMEL Corporation – 8-bit Microcontroller with 64K Bytes In- System Programmable Flash

20. Analog Comparator
The Analog Comparator compares the input values on the positive pin AIN0 and negative pin
AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin
AIN1, the Analog Comparator output, ACO, is set. The comparator’s output can be set to trigger
the Timer/Counter1 Input Capture function. In addition, the comparator can trigger a separate
interrupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on com-
parator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is
shown in Figure 20-1.
The Power Reduction ADC bit, PRADC, in ”PRR – Power Reduction Register” on page 43 must
be disabled by writing a logical zero to be able to use the ADC input MUX.
Figure 20-1. Analog Comparator Block Diagram⁽²⁾
BANDGAP
REFERENCE
ACBG
ACME
ADEN
ADC MULTIPLEXER
OUTPUT ⁽¹⁾
20.0.1
Notes: 1. See Table 20-2 on page 232.
2. Refer to Figure 1-1 on page 2 and Table 12-5 on page 77 for Analog Comparator pin
placement.
ADCSRB – ADC Control and Status Register B
Bit
(0x7B)
Read/Write
Initial Value
7
6
5
–
ACME
–
R
R/W
R
0
0
0
4
3
2
1
0
–
MUX5
ADTS2 ADTS1 ADTS0 ADCSRB
R
R/W
R/W
R/W
R/W
0
0
0
0
0
20.0.2
• 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
description of this bit, see ”Analog Comparator Multiplexed Input” on page 232.
ACSR – Analog Comparator Control and Status Register
Bit
0x30 (0x50)
Read/Write
Initial Value
7
6
5
4
3
2
1
0
ACD
ACBG
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
ACSR
R/W
R/W
R
R/W
R/W
R/W
R/W
R/W
0
0
N/A
0
0
0
0
0
230 ATmega644
2593L–AVR–02/07