ATmega16U4 datasheet(290/408 Pages) ATMEL

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290

7766D–AVR–01/09

ATmega16U4/ATmega32U4

23. Analog Comparator

The Analog Comparator compares the input values on the positive pin AIN+ and negative pin

AIN-. When the voltage on the positive pin AIN+ is higher than the voltage on the negative pin

AIN-, 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 23-1.

AIN+ can be connected either to the AIN0 (PE6) pin, or to the internal Bandgap reference. AIN-

can only be connected to the ADC multiplexer.

The Power Reduction ADC bit, PRADC, in “Power Reduction Register 0 - PRR0” on page 44

must be disabled by writing a logical zero to be able to use the ADC input MUX.

Figure 23-1. Analog Comparator Block Diagram

(2)

Notes:

1. See Table 23-2 on page 292.

2. Refer to “Pinout ATmega16U4/ATmega32U4” on page 3 and Table 10-3 on page 71 for Ana-

log Comparator pin placement.

23.0.1

ADC Control and Status Register B – ADCSRB

• 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 is connected to the negative input to the Analog Comparator. When this bit is

written logic zero, the Bandgap reference is connected to the negative input of the Analog Com-

parator (See “Internal Voltage Reference” on page 53.). For a detailed description of this bit, see

“Analog Comparator Multiplexed Input” on page 292.

23.0.2

Analog Comparator Control and Status Register – ACSR

ACBG

BANDGAP

REFERENCE

ADC MULTIPLEXER

OUTPUT

ACME

ADEN

(1)

AIN+

AIN-

BANDGAP

REFERENCE

Bit

3210

–ACME

–

ADTS2

ADTS1

ADTS0

ADCSRB

Read/Write

R/W

Initial Value

0000

Bit

7654

ACD

ACBG

ACO

ACI

ACIE

ACIC

ACIS1

ACIS0

ACSR

Read/Write

R/W

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