AT90USB82/162
22. 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 22-1. User can also replace by software the AIN0 input by the internal Bandgap
reference.
Figure 22-1. Analog Comparator Block Diagram(1)
BANDGAP
REFERENCE
ACBG
Notes: 1. Refer to Figure 1-1 on page 3 and Table 11-9 on page 79 for Analog Comparator pin
placement.
22.0.1
Analog Comparator Control and Status Register – ACSR
Bit
7
6
5
4
3
2
1
0
ACD
ACBG
ACO
ACI
ACIE
R/W
0
ACIC
R/W
0
ACIS1
R/W
0
ACIS0
R/W
0
ACSR
Read/Write
Initial Value
R/W
0
R/W
0
R
R/W
0
N/A
• 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. See “Internal Voltage Reference” on page 52.
• Bit 5 – ACO: Analog Comparator Output
The output of the Analog Comparator is synchronized and then directly connected to ACO. The
synchronization introduces a delay of 1 - 2 clock cycles.
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7707D–AVR–07/08
ATMEL [ ATMEL ]
