AT90S/LS4434 and AT90S/LS8535
60
Analog Comparator
The Analog Comparator compares the input values on the positive input PB2 (AIN0) and negative input PB3 (AIN1). When
the voltage on the positive input PB2 (AIN0) is higher than the voltage on the negative input PB3 (AIN1), the Analog Com-
parator Output (ACO) is set (one). 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 comparator output rise, fall or toggle. A block diagram of the comparator and its surrounding
logic is shown in Figure 44
Figure 44.
Analog Comparator Block Diagram
Analog Comparator Control and Status Register – ACSR
•
Bit 7 – ACD: Analog Comparator Disable
When this bit is set (one), the power to the Analog Comparator is switched off. This bit can be set at any time to turn off the
Analog Comparator. 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 – Res: Reserved Bit
This bit is a reserved bit in the AT90S4434/8535 and will always read as zero.
•
Bit 5 – ACO: Analog Comparator Output
ACO is directly connected to the comparator output.
•
Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set (one) when a comparator output event triggers the interrupt mode defined by ACI1 and ACI0. The Analog
Comparator Interrupt routine is executed if the ACIE bit is set (one) and the I-bit in SREG is set (one). ACI is cleared by
hardware when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logical “1”
to the flag.
•
Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is set (one) and the I-bit in the Status Register is set (one), the Analog Comparator interrupt is activated.
When cleared (zero), the interrupt is disabled.
•
Bit 2 – ACIC: Analog Comparator Input Capture Enable
When set (one), this bit enables the Input Capture function in Timer/Counter1 to be triggered by the Analog Comparator.
The comparator output is in this case directly connected to the Input Capture front-end logic, making the comparator utilize
the noise canceler and edge select features of the Timer/Counter1 Input Capture interrupt. When cleared (zero), no
Bit
7
6
5
4
3
2
1
0
$08 ($28)
ACD
–
ACO
ACI
ACIE
ACIC
ACIS1
ACIS0
ACSR
Read/Write
R/W
R
R
R/W
R/W
R/W
R/W
R/W
Initial value
0
0
N/A
0
0
0
0
0