Microchip Technology dsPIC DSC DTMF, Руководство пользователя

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©
2008 Microchip Technology Inc. DS70332A-page 7
dsPIC
®
DSC DTMF DETECTION
LIBRARY USER’S GUIDE
Chapter 1. Introduction
The dsPIC DSC DTMF Detection Library provides an algorithm that detects the Dual
Tone Multi-Frequency (DTMF) signals.
This chapter explains the basic concepts to help
you implement the dsPIC DSC DTMF Detection Library in your application. This chap-
ter also discusses the principle of DTMF tone detection. Topics covered include:
• Overview
• DTMF Signal and Frequencies
• Principle of Detection
• DTMF Tone Detector
• Applications and Performance
1.1 OVERVIEW
The dsPIC DSC DTMF Detection Library has been developed in accordance with
ITU-T Q.24 Multi-Frequency Push-Button Signal Reception recommendations. Full
source code is provided to fulfill the following objectives:
• To help you jump start your application with plug-in code
• To facilitate customization to satisfy your specific requirements
To help meet these objectives, a sample application program running on a dsPIC33F
device is analyzed in
Chapter 4. “DTMF Detection Demonstration” . This sample
program demonstrates the remote DTMF signal detection over a dial-up phone line. In
this demonstration, the dsPICDEM.net board is dialed from a telephone. The
Si3034/Si3035 DAA/AFE telephone interface detects the ring signal and alerts the
dsPIC33F device, which initializes the program.
1.2 DTMF SIGNAL AND FREQUENCIES
A DTMF signal consists of two main frequency components:
• Low Frequency
• High Frequency
Figure 1-1 shows a DTMF signal consisting of a burst that combines one tone from the
Low Frequency group and another tone from the High Frequency group. The burst can
be formed by using any of the 16 possible combinations.
The tone burst is followed by
a silence period. The minimum tone duration of a DTMF tone and pause period is
40 ms as specified in the ITU-T Recommendation Q.24 AT&T standard.
.
TABLE 1-1: DTMF KEY PAD AND ASSOCIATED FREQUENCIES
Frequency (Hz) 1209 1339 1477 1633
697 1 2 3 A
770 4 5 6 B
852 7 8 9 C
941 * 0 # D