ATtiny261/461/861

• 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.

• Bit 4 – ACI: Analog Comparator Interrupt Flag

This bit is set by hardware when a comparator output event triggers the interrupt mode defined by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is set and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.

• Bit 3 – ACIE: Analog Comparator Interrupt Enable

When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog Comparator interrupt is activated. When written logic zero, the interrupt is disabled.

• Bit 2 – 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 140.

• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select

These bits determine which comparator events that trigger the Analog Comparator interrupt. The different settings are shown in Table 18-1.

Table 18-1.	ACIS1/ACIS0 Settings
ACIS1	ACIS0	Interrupt Mode
0	0	Comparator Interrupt on Output Toggle.
0	1	Reserved
1	0	Comparator Interrupt on Falling Output Edge.
1	1	Comparator Interrupt on Rising Output Edge.

When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by clearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt can occur when the bits are changed.

18.2Analog Comparator Multiplexed Input

When the Analog to Digital Converter (ADC) is configurated as single ended input channel, it is possible to select any of the ADC10..0 pins to replace the negative input to the Analog Comparator. The ADC multiplexer is used to select this input, and consequently, the ADC must be switched off to utilize this feature. If the Analog Comparator Multiplexer Enable bit (ACME in ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is zero), MUX5..0 in ADMUX select the input pin to replace the negative input to the Analog Comparator, as shown in Table

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18-2. If ACME is cleared or ADEN is set, either AIN0, AIN1 or AIN2 is applied to the negative input to the Analog Comparator.

Table 18-2.	Analog Comparator Multiplexed Input
ACME	ADEN	MUX5..0	ACM2..0	Positive Input	Negative Input
0	x	xxxxxx	000	AIN0	AIN1
0	x	xxxxxx	001	AIN0	AIN2
0	x	xxxxxx	010	AIN1	AIN0
0	x	xxxxxx	011	AIN1	AIN2
0	x	xxxxxx	100	AIN2	AIN0
0	x	xxxxxx	101,110,111	AIN2	AIN1
1	1	xxxxxx	000	AIN0	AIN1
1	0	000000	000	AIN0	ADC0
1	0	000000	01x	AIN1	ADC0
1	0	000000	1xx	AIN2	ADC0
1	0	000001	000	AIN0	ADC1
1	0	000001	01x	AIN1	ADC1
1	0	000001	1xx	AIN2	ADC1
1	0	000010	000	AIN0	ADC2
1	0	000010	01x	AIN1	ADC2
1	0	000010	1xx	AIN2	ADC2
1	0	000011	000	AIN0	ADC3
1	0	000011	01x	AIN1	ADC3
1	0	000011	1xx	AIN2	ADC3
1	0	000100	000	AIN0	ADC4
1	0	000100	01x	AIN1	ADC4
1	0	000100	1xx	AIN2	ADC4
1	0	000101	000	AIN0	ADC5
1	0	000101	01x	AIN1	ADC5
1	0	000101	1xx	AIN2	ADC5
1	0	000110	000	AIN0	ADC6
1	0	000110	01x	AIN1	ADC6
1	0	000110	1xx	AIN2	ADC6
1	0	000111	000	AIN0	ADC7
1	0	000111	01x	AIN1	ADC7
1	0	000111	1xx	AIN2	ADC7
1	0	001000	000	AIN0	ADC8
1	0	001000	01x	AIN1	ADC8
1	0	001000	1xx	AIN2	ADC8

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Table 18-2.	Analog Comparator Multiplexed Input (Continued)
ACME	ADEN	MUX5..0	ACM2..0	Positive Input	Negative Input
1	0	001001	000	AIN0	ADC9
1	0	001001	01x	AIN1	ADC9
1	0	001001	1xx	AIN2	ADC9
1	0	001010	000	AIN0	ADC10
1	0	001010	01x	AIN1	ADC10
1	0	001010	1xx	AIN2	ADC10

18.2.1ACSRB – Analog Comparator Control and Status Register B

Bit		7	6	5	4	3	2	1	0
0x09 (0x29)		HSEL	HLEV	-	-	-	ACM2	ACM1	ACM0	ACSRB
Read/Write		R/W	R/W	R	R	R	R/W	R/W	R/W
Initial Value		0	0	N/A	0	0	0	0	0

• Bit 7 – HSEL: Hysteresis Select

When this bit is written logic one, the hysteresis of the Analog Comparator is switched on. The hysteresis level is selected by the HLEV bit.

• Bit 6 – HLEV: Hysteresis Level

When the hysteresis is enabled by the HSEL bit, the Hysteresis Level, HLEV, bit selects the hysteresis level that is either 20mV (HLEV=0) or 50mV (HLEV=1).

• Bit 2:0 – ACM2:ACM0: Analog Comparator Multiplexer

The Analog Comparator multiplexer bits select the positive and negative input pins of the Analog Comparator. The different settings are shown in Table 18-2.

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19. ADC – Analog to Digital Converter

19.1Features

•10-bit Resolution

•1.0 LSB Integral Non-linearity

•± 2 LSB Absolute Accuracy

•65 - 260 µs Conversion Time

•Up to 15 kSPS at Maximum Resolution

•11 Multiplexed Single Ended Input Channels

•16 Differential input pairs

•15 Differential input pairs with selectable gain

•Temperature sensor input channel

•Optional Left Adjustment for ADC Result Readout

•0 - VCC ADC Input Voltage Range

•Selectable 1.1V / 2.56V ADC Voltage Reference

•Free Running or Single Conversion Mode

•ADC Start Conversion by Auto Triggering on Interrupt Sources

•Interrupt on ADC Conversion Complete

•Sleep Mode Noise Cancele

•Unipolar / Bibolar Input Mode

•Input Polarity Reversal Mode

19.2Overview

The ATtiny261/461/861 features a 10-bit successive approximation ADC. The ADC is connected to a 11-channel Analog Multiplexer which allows 16 differential voltage input combinations and 11 single-ended voltage inputs constructed from the pins PA7..PA0 or PB7..PB4. The differential input is equipped with a programmable gain stage, providing amplification steps of 1x, 8x, 20x or 32x on the differential input voltage before the A/D conversion. The single-ended voltage inputs refer to 0V (GND).

The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is held at a constant level during conversion. A block diagram of the ADC is shown in Figure 19-1.

Internal reference voltages of nominally 1.1V or 2.56V are provided On-chip. The Internal referance voltage of 2.56V, can optionally be externally decoupled at the AREF (PA3) pin by a capacitor, for better noise performance. Alternatively, VCC can be used as reference voltage for single ended channels. There is also an option to use an external voltage reference and turn-off the internal voltage reference. These options are selected using the REFS2:0 bits of the ADMUX control register.

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