ATtiny13A datasheet(92/174 Pages) ATMEL

92 / 174 page

8126D–AVR–11/09

ATtiny13A

• Quantization Error: Due to the quantization of the input voltage into a finite number of codes,

a range of input voltages (1 LSB wide) will code to the same value. Always ± 0.5 LSB.

• Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition compared to

an ideal transition for any code. This is the compound effect of offset, gain error, differential

error, non-linearity, and quantization error. Ideal value: ± 0.5 LSB.

14.11 ADC Conversion Result

After the conversion is complete (ADIF is high), the conversion result can be found in the ADC

Result Registers (ADCL, ADCH).

For single ended conversion, the result is

where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see

Table 14-2 on page 92 and Table 14-3 on page 93). 0x000 represents analog ground, and

0x3FF represents the selected reference voltage minus one LSB.

14.12 Register Description

14.12.1

ADMUX – ADC Multiplexer Selection Register

• Bits 7, 4:2 – Res: Reserved Bits

These bits are reserved bits in the ATtiny13A and will always read as zero.

• Bit 6 – REFS0: Reference Selection Bit

This bit selects the voltage reference for the ADC, as shown in Table 14-2. If this bit is changed

during a conversion, the change will not go in effect until this conversion is complete (ADIF in

ADCSRA is set).

• Bit 5 – ADLAR: ADC Left Adjust Result

The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register.

Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing the

ADLAR bit will affect the ADC Data Register immediately, regardless of any ongoing conver-

sions. For a complete description of this bit, see “ADCL and ADCH – The ADC Data Register” on

page 94.

ADC

VIN 1024

⋅

VREF

--------------------------

Bit

65432

0x07

–

REFS0

ADLAR

–

MUX1

MUX0

ADMUX

Read/Write

R/W

Initial Value

00000

Table 14-2.

Voltage Reference Selections for ADC

REFS0

Voltage Reference Selection

0VCC used as analog reference.

Internal Voltage Reference.

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