ST72361 datasheet(169/224 Pages) STMICROELECTRONICS

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ST72361

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10.9 10-BIT A/D CONVERTER (ADC)

10.9.1 Introduction

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

ripheral is a 10-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 10-bit

Data Register. The A/D converter is controlled

through a Control/Status Register.

10.9.2 Main Features

■ 10-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 94.

10.9.3 Functional Description

10.9.3.1 Digital A/D Conversion Result

The conversion is monotonic, meaning that the re-

sult never decreases if the analog input does not

and never increases if the analog input does not.

If the input voltage (VAIN) is greater than VDDA

(high-level voltage reference) then the conversion

result is FFh in the ADCDRH register and 03h in

the ADCDRL register (without overflow indication).

If the input voltage (VAIN) is lower than VSSA (low-

level voltage reference) then the conversion result

in the ADCDRH and ADCDRL registers is 00 00h.

The A/D converter is linear and the digital result of

the conversion is stored in the ADCDRH and AD-

CDRL registers. The accuracy of the conversion is

described in the Electrical Characteristics Section.

RAIN is the maximum recommended impedance

for an analog input signal. If the impedance is too

high, this will result in a loss of accuracy due to

leakage and sampling not being completed in the

allotted time.

Figure 94. ADC Block Diagram

CH2

CH1

EOC SPEED ADON SLOW

CH0

ADCCSR

AIN0

AIN1

ANALOG TO DIGITAL

CONVERTER

AINx

ANALOG

MUX

ADCDRH

fADC

fCPU

ADCDRL

CH3

fCPU, fCPU/2, fCPU/4

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