Datasheet

194
ATmega325/3250/645/6450
2570K–AVR–04/07
Analog Comparator The Analog Comparator compares the input values on the positive pin AIN0 and nega-
tive 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 comparator output rise, fall or toggle. A block dia-
gram of the comparator and its surrounding logic is shown in Figure 83.
The Power Reduction ADC bit, PRADC, in “Power Reduction Register” on page 35 must
be disabled by writing a logical zero to be able to use the ADC module.
Figure 83. Analog Comparator Block Diagram
(2)
Notes: 1. See Table 84 on page 196.
2. Refer to Figure 1 on page 2, Figure 2 on page 3, and “Alternate Functions of Port E”
on page 70 for Analog Comparator pin placement.
ADCSRB – ADC Control and
Status Register B
• 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 Compar-
ator. For a detailed description of this bit, see “Analog Comparator Multiplexed Input” on
page 196.
ACSR – Analog Comparator
Control and Status Register
ACBG
BANDGAP
REFERENCE
ADC MULTIPLEXER
OUTPUT
ACME
ADEN
(1)
Bit 7 6543210
(0x7B)
– ACME – – – ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R R/W R R R R/W R/W R/W
Initial Value0 0000000
Bit 76543210
0x30 (0x50) ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 ACSR
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value 0 0 N/A 0 0 0 0 0