ST72C254G2 datasheet(86/140 Pages) STMICROELECTRONICS

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ST72104G, ST72215G, ST72216G, ST72254G

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12.5 8-BIT A/D CONVERTER (ADC)

12.5.1 Introduction

The on-chip Analog to Digital Converter (ADC) pe-

ripheral is a 8-bit, successive approximation con-

verter with internal sample and hold circuitry. This

peripheral has up to 16 multiplexed analog input

channels (refer to device pin out description) that

allow the peripheral to convert the analog voltage

levels from up to 16 different sources.

The result of the conversion is stored in a 8-bit

Data Register. The A/D converter is controlled

through a Control/Status Register.

12.5.2 Main Features

8-bit conversion

Up to 16 channels with multiplexed input

Linear successive approximation

Data register (DR) which contains the results

Conversion complete status flag

On/off bit (to reduce consumption)

The block diagram is shown in Figure 1.

12.5.3 Functional Description

12.5.3.1 Analog Power Supply

VDDA and VSSA are the high and low level refer-

ence voltage pins. In some devices (refer to device

pin out description) they are internally connected

to the VDD and VSS pins.

Conversion accuracy may therefore be impacted

by voltage drops and noise in the event of heavily

loaded or badly decoupled power supply lines.

See electrical characteristics section for more de-

tails.

Figure 47. ADC Block Diagram

CH2

CH1

CH3

COCO

ADON

CH0

ADCCSR

AIN0

AIN1

ANALOG TO DIGITAL

CONVERTER

AINx

ANALOG

MUX

RADC

CADC

ADCDR

DIV 2

fADC

fCPU

HOLD CONTROL

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