ATtiny261A datasheet(147/292 Pages) ATMEL

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8197A–AVR–10/09

ATtiny261A/461A/861A

selection. Since the next conversion has already started automatically, the next result will reflect

the previous channel selection. Subsequent conversions will reflect the new channel selection.

15.6.2

ADC Voltage Reference

The conversion range of the ADC is defined by the voltage reference (VREF). Single ended chan-

nels that exceed VREF will result in codes close to 0x3FF. VREF can be selected as either VCC, or

internal 1.1V / 2.56V voltage reference, or external AREF pin. The first conversion result after

switching voltage reference source may be inaccurate, and the user is advised to discard this

result.

15.7 ADC Noise Canceler

The ADC features a noise canceler that enables conversion during sleep mode. This reduces

noise induced from the CPU core and other I/O peripherals. The noise canceler can be used

with ADC Noise Reduction and Idle mode. To make use of this feature, the following procedure

should be used:

• Make sure that the ADC is enabled and is not busy converting. Single Conversion mode must

be selected and the ADC conversion complete interrupt must be enabled.

• Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the

CPU has been halted.

• If no other interrupts occur before the ADC conversion completes, the ADC interrupt will

wake up the CPU and execute the ADC Conversion Complete interrupt routine. If another

interrupt wakes up the CPU before the ADC conversion is complete, it will be executed, and

an ADC Conversion Complete interrupt request will be generated when the ADC conversion

completes. The CPU will remain in active mode until a new sleep command is executed.

Note that the ADC will not automatically be turned off when entering other sleep modes than Idle

mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before enter-

ing such sleep modes to avoid excessive power consumption.

15.8 Analog Input Circuitry

The analog input circuitry for single ended channels is illustrated in Figure 15-8 An analog

source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regard-

less of whether that channel is selected as input for the ADC. When the channel is selected, the

source must drive the S/H capacitor through the series resistance (combined resistance in the

input path).

ATtiny261A Datasheet(PDF) 147 Page - ATMEL Corporation