
149
2543L–AVR–08/10
ATtiny2313
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
Figure 66. Analog Comparator Block Diagram
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. 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 is used as input to the Analog Comparator, it will take a
certain time for the voltage to stabilize. If not stibilized, the first conversion may give a wrong
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.
Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode defined
by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is set
and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding inter-
rupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
Bit 3 – ACIE: Analog Comparator Interrupt Enable
ACBG
BANDGAP
REFERENCE
Bit
765
4321
0
ACD
ACBG
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
ACSR
Read/Write
R/W
R
R/W
Initial Value
0
N/A
0000
0