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20. Analog Comparator
The Analog Comparator compares the input values on the positive pin AIN0 and negative pin
AIN1.
20.1 Overview
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 inter-
rupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on comparator
output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown
in Figure 20-1.
Figure 20-1. Analog Comparator Block Diagram
(1)(2)
Notes: 1. ADC multiplexer output: see Table 20-2 on page 271.
2. Refer to Figure 1-2 on page 5 or Figure 1-3 on page 6 and Table 9-15 on page 83 for Analog
Comparator pin placement.
20.2 Analog Comparator Register Description
20.2.1 ADC Control and Status Register B – ADCSRB
• 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 271.
ACBG
BANDGAP
REFERENCE
ADC
MULTIPLEXER
OUTPUT
ACME
ADEN
T/C1 INPUT CAPTURE
Bit 76543210
- ACME – – – ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R R/W R R R R/W R/W R/W
Initial Value00000000
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