Commodore 128 Programmer's Reference Manual page 113

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ONE STEP BEYOND SIMPLE BASIC 103
ADVANCED BASIC
- PROGRAMMING TECHNIQUES
FOR COMMODORE MODEMS
I | The following information tells you how to:
^ 1. Generate Touch Tone™ frequencies
! I 2. Detect telephone ringing
■ ■ ' 3. Program the telephone to be on or off the hook
4. Detect carrier
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I j The programming procedures operate in C128 or C64 modes with the Modem/300.
In C128 mode, select a bank configuration which contains BASIC, I/O, and the Kernal.
R GENERATING TOUCH TONE
(DTMF) FREQUENCIES
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Each button on the face of a Touch Tone telephone generates a different pair of tones
(frequencies). You can simulate these tones with your Commodore 128 computer. Each
button has a row and column value in which you must store the appropriate memory
location in order to output the correct frequency. Here are the row and column
frequency values that apply to each button on the face of your Touch Tone telephone:
TOUCH TONE FREQUENCY TABLE
COLUMN 1 (1029 HZ) COLUMN 2 (1336 HZ) COLUMN 3 (1477 HZ)
Row 1(697 Hz) 1 2 3
Row 2 (770 Hz) 4 5 6
Row 3 (852 Hz) 7 8 9
Row 4 (941 Hz) * 0 #
To generate these tones in BASIC with your Commodore 128, follow this procedure:
1. Initialize the sound (SID) chip with the following BASIC statements:
SID = 54272
POKE SID + 24,15:POKE SID + 4,16
POKE SID + 11,16:POKESID + 5,0:POKE SID + 12,0
POKE SID + 6,15*16:POKESID + 13,15*16:POKE SID + 23,0
2. Next, select one row and one column value for each digit in the telephone
number. The POKE statement for each row and column are as follows: