AT90USB646 datasheet(329/434 Pages) ATMEL

329 / 434 page

329

7593A–AVR–02/06

AT90USB64/128

Example 1:

– ADMUX = 0xED (ADC3 - ADC2, 10x gain, 2.56V reference, left adjusted result)

– Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.

– ADCR = 512 * 10 * (300 - 500) / 2560 = -400 = 0x270

– ADCL will thus read 0x00, and ADCH will read 0x9C.

Writing zero to ADLAR right adjusts the result: ADCL = 0x70, ADCH = 0x02.

Example 2:

– ADMUX = 0xFB (ADC3 - ADC2, 1x gain, 2.56V reference, left adjusted result)

– Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.

– ADCR = 512 * 1 * (300 - 500) / 2560 = -41 = 0x029.

– ADCL will thus read 0x40, and ADCH will read 0x0A.

Writing zero to ADLAR right adjusts the result: ADCL = 0x00, ADCH = 0x29.

25.8 ADC Register Description

25.8.1

ADC Multiplexer Selection Register – ADMUX

• Bit 7:6 – REFS1:0: Reference Selection Bits

These bits select the voltage reference for the ADC, as shown in Table 25-3. If these bits are

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

Table 25-2.

Correlation Between Input Voltage and Output Codes

VADCn

Read code

Corresponding decimal value

VADCm + VREF /GAIN

0x1FF

511

ADCm + 0.999 VREF /GAIN

0x1FF

511

VADCm + 0.998 VREF /GAIN

0x1FE

510

...

ADCm + 0.001 VREF /GAIN

0x001

VADCm

0x000

ADCm - 0.001 VREF /GAIN

0x3FF

-1

...

VADCm - 0.999 VREF /GAIN

0x201

-511

ADCm - VREF /GAIN

0x200

-512

Bit

765

4321

REFS1

REFS0

ADLAR

MUX4

MUX3

MUX2

MUX1

MUX0

ADMUX

Read/Write

R/W

Initial Value

000

0000

AT90USB646 Datasheet(PDF) 329 Page - ATMEL Corporation

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