70
ATmega103(L)
0945G–09/01
Analog Comparator
The analog comparator compares the input values on the positive input PE2 (AC+) and
negative input PE3 (AC-). When the voltage on the positive input PE2 (AC+) is higher
than the voltage on the negative input PE3 (AC-), the Analog Comparator Output (ACO)
is set (one). The output of the comparator 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. This will reduce power con-
sumption 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 – Res: Reserved Bit
This bit is a reserved bit in the ATmega103(L) 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 execut-
ing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a
logical “1” to the flag. Observe, however, that if another bit in this register is modified
PE2
(AC+)
PE3
(AC-)
+
-
ACO
ACI
INTERRUPT
SELECT
ACIS1
ACIS0
ACIE
ACIC
ANALOG
COMPARATOR
IRQ
TO T/C1 CAPTURE
TRIGGER MUX
VCC
ACD
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
X
0
0
0
0
0