User`s guide

MPLAB Starter Kit for dsPIC

DSCs User’s Guide

2.2 UNDERSTANDING THE DEMO

The dsPIC33F device on the starter kit is pre-programmed with a Speech Record and

Playback Demonstration application. The CD that accompanies the starter kit contains

the application code. As shown in Figure 2-1, this sample application uses the board to

capture an input microphone signal using the audio codec. The application program

running on the device does the following:

• Reads an introductory speech message stored on the serial Flash memory and

uses the audio codec to play back the audio signal.

• If speech recording is desired, the application compresses the incoming digital

signal from 16 bits to 8 bits using the G.711 μ-law encoding algorithm and stores

the encoded speech samples on the serial flash memory.

• If playback is desired, the application reads the serial Flash memory device and

decodes the read samples using the G.711 μ-law decoding algorithm. The

application then uses the audio codec to play back the speech signal.

FIGURE 2-1: SPEECH RECORD AND PLAYBACK DEMO OVERVIEW

The board also features circuitry for audio playback using the Pulse-Width Modulation

technique. This technique can be used to implement a low-cost audio playback system.

For a demo of this technique, access the starter kit’s CD-ROM.

The demo program consists of three basic software elements: WM8510 Codec Driver,

G.711 Speech Encoder and Decoder, and Serial Flash Memory Driver.

2.2.1 WM8510 Codec Driver

The WM8510 Codec Driver configures the WM8510 audio codec and provides an inter-

face for reading and writing audio data to the codec. The driver is implemented in

WM8510CodecDrv.c and the interface is defined in WM8510CodecDrv.h. The driver

uses the DCI module on the dsPIC33F device module to process data and the I

C™

module as a codec control bus. The demo application configures the codec for a 8 KHz

sampling rate.

G.711

μ-LAW

ENCODE

DCI

dsPIC33F

STARTER KIT BOARD

AUDIO

CODEC

G.711

μ-LAW

DECODE

Serial Flash Memory

SPI

Data

Control

C™