November 2012

Doc ID 17566 Rev 3

1/13

AN3225

Application note

Audio software codec

for STM8L15xxx and STM8AL31xx/STM8AL3Lxx

Introduction

This application note describes a simple and easy-to-use solution to help design and

develop products with an audio output, for example, toys, alarms, door bells, and white

goods.

Audio data generally require the storage of a lot of memory. However, the memory space

needed to preserve such data can be reduced by compressing the audio data via a

specified compression method. Processing these data is usually a complex task requiring

powerful microcontrollers such as DSP or audio chip. Normally, 8-bit microcontrollers do not

offer either a large memory or a high computing performance.

The software solution offered in this application note reconstructs audio signals from

compressed samples. A simple audio codec based on an adaptive differential pulse coded

modulation (ADPCM) algorithm is used and advantage is taken of the advanced

STM8L/STM8AL core with its 3-staged pipeline and 16 MIPS peak performance.

The digital samples are converted to an analog signal by an on-chip, 12-bit, digital-to-analog

converter (DAC). This offers good overall audio quality, yet is a cost-effective solution for 8-

bit microcontroller applications.

The battery-powered application benefits from the ultra low-power consumption of

STM8L/STM8AL microcontrollers.

The example firmware and application hardware design are provided with this application

note to enable easy porting of the offered solution to the final application.

Table 1 summarizes the products covered by this application note.

Table 1.

Applicable products

Product family

Part numbers

Microcontrollers

– STM8L151x4, STM8L151x6, STM8L152x4, STM8L152x6

– STM8L151x8, STM8L152x8, STM8L151R6, STM8L152R6,

STM8L162R8, STM8L162M8

– STM8AL313x, STM8AL314x, STM8AL316x, STM8AL3L4x,

STM8AL3L6x

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