ATmega1284P datasheet(238/380 Pages) ATMEL

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238

8059D–AVR–11/09

ATmega1284P

20.3

20.3.1

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 Comparator. For a detailed

description of this bit, see ”Analog Comparator Multiplexed Input” on page 237.

20.3.2

ACSR – Analog Comparator Control and Status Register

• 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 bandgap reference is used as input to the Analog Comparator, it will take a certain

time for the voltage to stabilize. If not stabilized, the first conversion may give wrong value. See

”Internal Voltage Reference” on page 52.

• 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.

001

ADC1

010

ADC2

011

ADC3

100

ADC4

101

ADC5

110

ADC6

111

ADC7

Table 20-1.

Analog Comparator Mulitiplexed Input

ACME

ADEN

MUX2..0

Analog Comparator Negative Input

Bit

432

(0x7B)

–

ACME

–

MUX5

ADTS2

ADTS1

ADTS0

ADCSRB

Read/Write

R/W

Initial Value

Bit

76543210

0x30 (0x50)

ACD

ACBG

ACO

ACI

ACIE

ACIC

ACIS1

ACIS0

ACSR

Read/Write

R/W

Initial Value

N/A

00000

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