L9803 datasheet(69/126 Pages) STMICROELECTRONICS

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L9803

On-Chip Peripherals

69/126

5.5

10-BIT A/D Converter (AD10)

5.5.1

Introduction

The Analog to Digital converter is a single 10-bit successive approximation converter with 4

input channels. Analog voltage from external sources are input to the converter through

AD2,AD3 and AD4 pins. Channel 1 (AD1) is connected to the internal temperature sensor

(see Section 5.5.5).

Note:

The anti aliasing filtering must be accomplished using an external RC filter. The internal

AD1 channel is filtered by an RC network with approx. 1

µs time constant.

5.5.2

Functional Description

The result of the conversion is stored in 2 registers: the Data Register High (ADCDRH) and

the Data Register Low (ADCDRL).

The A/D converter is enabled by setting the ADST bit in ADCCSR Register. Bits CH1 and

CH0 of ADCCSR Register select the channel to be converted. The high and low reference

voltage are connected to pins VCC and AGND.

When enabled, the A/D converter performs a complete conversion in 14

µs (with system

clock fCPU=8Mhz). The total conversion time includes multiplex, sampling of the input

voltage, 10-bit conversion and writing DRH and DRL registers.

When the conversion is completed COCO bit (COnversion COmpleted) is set in ADCCSR.

A conversion starts from the moment ADST bit is set. When a conversion is running it is

possible to write the ADCCSR without stopping the ADC operations, because all the data in

ADCCSR are latched when ADST is set. This property allows to select a different channel to

be processed during the next conversion or to manage the interrupt enable bit. The new

setting will have effect on the next conversion (including interrupt generation)

At the end of the conversion ADST is reset and COCO bit is set.

Note:

To start a new conversion the ADST must be set after the completion of the current one. Any

writing to ADST when a conversion is running (COCO=0) has no effect since ADST bit is

automatically reset by the end of conversion event.

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