108
7598H–AVR–07/09
ATtiny25/45/85
17. 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 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 17-1.
Figure 17-1. Analog Comparator Block Diagram
(2)
Notes: 1. See Table 17-2 on page 110.
2. Refer to Figure 1-1 on page 2 and Table 10-5 on page 57 for Analog Comparator pin
placement.
17.1 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 110.
17.2 Analog Comparator Control and Status Register – ACSR
• 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.
ACBG
BANDGAP
REFERENCE
ADC MULTIPLEXER
OUTPUT
ACME
ADEN
(1)
Bit 76543210
BIN ACME IPR – – ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R R/W R R R R/W R/W R/W
Initial Value 0 0000000
Bit 76543210
ACD ACBG ACO ACI ACIE – ACIS1 ACIS0 ACSR
Read/Write R/W R/W R R/W R/W R R/W R/W
Initial Value00N/A00000
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