DTMF TONE GENERATION USING CCPMANY APPLICATIONS MICROPROCESSOR MUST AC

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DTMF TONE GENERATION USING CCPMANY APPLICATIONS MICROPROCESSOR MUST AC

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APPLICATION NOTE DTMF TONE GENERATION
DTMF TONE GENERATION USING CCPMANY APPLICATIONS MICROPROCESSOR MUST ACCESS PHONE LINES COMMUNICATIONS DATA EXCHANGE. Z8'S PULSE WIDTH MODULATION CAPABILITIES ALLOW DTMF TONE GENERATION SOFTWARE.
INTRODUCTION THEORY OPERATION
program outlined below generates DTMF tones using pulse width modulation (PWM) algorithm. used vary level output varying duty cycle (the "on" time divided cycle period) square wave. Varying "on" time sine function then feeding output through lowpass filter yields sine wave. Sine values determined Basic program Listing sine table contains entries, which turn contain hexadecimal values representing sine function degrees. These values indexed loaded into sampling rate that, according Nyquist, must least twice highest frequency tone that want reproduce. Since highest frequency this application 1477 sampling rate must least twice this, 2954 samples second. higher sampling rate, greater accuracy. example illustrated here sample rate 12000 samples second used both higher accuracy ease filtering. Since are, effect, producing tones, pointers used fetch next value look-up table: frequencies, column frequencies. frequency resulting sine wave calculated multiplying number steps sine look-up table (256) desired frequency, divided sampling rate. This offset value added current pointer, which then fetches next number from look-up table. This done both column frequencies. added, then loaded into timer register (T1). lowpass filter chosen have corner frequency lowest column frequency, 1209 this point, column frequencies will least below frequencies. However, telephone lines themselves large-scale lowpass filter, time tones reach telephone switching equipment, amplitude should same. spec therefore calls column frequencies higher than frequencies. telephone industry this known "twist." This adjustment made software taking value from look-up table column frequency doing "rotate left." This results twice amplitude column frequency gain, from frequency, just where want Overall level from output lowpass filter adjusted with potentiometer.
AP96Z8X1200
APPLICATION NOTE DTMF TONE GENERATION
DTMF TONE GENERATION
12.00
XTAL
XTAL
DTMF
Column Column
Column
Z86C06
TELEPHONE KEYPAD MATRIX
AP96Z8X1200
APPLICATION NOTE DTMF TONE GENERATION
LISTING
AP96Z8X1200
APPLICATION NOTE DTMF TONE GENERATION
AP96Z8X1200
APPLICATION NOTE DTMF TONE GENERATION
AP96Z8X1200
APPLICATION NOTE DTMF TONE GENERATION
AP96Z8X1200
APPLICATION NOTE DTMF TONE GENERATION
AP96Z8X1200
APPLICATION NOTE DTMF TONE GENERATION
1997 Zilog, Inc. rights reserved. part this document copied reproduced form means without prior written consent Zilog, Inc. information this document subject change without notice. Devices sold Zilog, Inc. covered warranty patent indemnification provisions appearing Zilog, Inc. Terms Conditions Sale only. Zilog, Inc. makes warranty, express, statutory, implied description, regarding information forth herein regarding freedom described devices from intellectual property infringement. Zilog, Inc. makes warranty merchantability fitness purpose. Zilog, Inc. shall responsible errors that appear this document. Zilog, Inc. makes commitment update keep current information contained this document.
Zilog's products authorized critical components life support devices systems unless specific written agreement pertaining such intended executed between customer Zilog prior use. Life support devices systems those which intended surgical implantation into body, which sustains life whose failure perform, when properly used accordance with instructions provided labeling, reasonably expected result significant injury user. Zilog, Inc. East Hacienda Ave. Campbell, 95008-6600 Telephone (408) 370-8000 Telex 910-338-7621 370-8056 Internet: http://www.zilog.com
AP96Z8X1200

DTMF TONE GENERATION USING CCPMANY APPLICATIONS MICROPROCESSOR MUST AC

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