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10-BIT A/D CONVERTER (ADC) (Cont’d)

10.7.3.4 A/D Conversion

Conversion can be performed in One-Shot or Con-

tinuous mode. Continuous mode is typically used

for monitoring a single channel. One-shot mode

should be used when the application requires in-

puts from several channels.

ADC Configuration

The analog input ports must be configured as in-

put, no pull-up, no interrupt. Refer to the «I/O

ports» chapter. Using these pins as analog inputs

does not affect the ability of the port to be read as

a logic input.

In the ADCCSR register:

– Select the CS[2:0] bits to assign the analog

channel to convert.

ADC One-Shot Conversion mode

In the ADCCSR register:

1.Set the ONE SHOT bit to put the A/D converter

in one shot mode.

2.Set the ADON bit to enable the A/D converter

and to start the conversion. The EOC bit is kept

low by hardware during the conversion.

Note: Changing the A/D channel during conver-

sion will stop the current conversion and start con-

version of the newly selected channel.

When a conversion is complete:

– The EOC bit is set by hardware.

– An interrupt request is generated if the ITE bit

is set.

– The ADON bit is reset by hardware.

– The result is in the ADCDR registers.

To read the 10 bits, perform the following steps:

1. Wait for interrupt or poll the EOC bit

2. Read ADCDRLSB

3. Read ADCDRMSB

The EOC bit is reset by hardware once the AD-

CDRMSB is read.

Figure 51. ADC Block Diagram

CS2

CS1

EOC SPEED ADON

ITE

CS0

ADCCSR

AIN0

AIN1

ANALOG TO DIGITAL

CONVERTER

AINx

ANALOG

MUX

ADCDRMSB

DIV 2

fADC

fCPU

ADCDRLSB

DIV 4

EOC Interrupt

0000

ONE

SHOT

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