Commodore modem 300 User Manual page 72

To generate these tones in BASIC with your Commodore 64 or
Commodore 128:
1) Initialize the sound (SID) chip with the following BASIC
statements:
sid = 54272
pokesid + 24,15: pokesid + 4,16
pokesid + 11,16:pokesid + 5,0:pokesid + 12,0
pokesid + 6,15*16:pokesid + 13,15*16: pokesid + 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:
Column1:pokesid,117:pokesid + 1,77
Column2:pokesid,152:pokesid + 1,85
Column3:pokesid,161:pokesid + 1,94
Row1:pokesid + 7,168:pokesid + 8,44
Row 2: poke sid + 7,85: poke sid + 8,49
Row3:pokesid + 7,150:pokesid + 8,54
Row 4: poke sid + 7,74: poke sid + 8,60
For example, to generate a tone for the number 1, poke the values
for row 1,column 1 as follows:
poke sid + 7,168: poke sid + 8,44:rem row 1
pokesid,117:pokesid + 1,77:remcolumn1
3) Turn on the tones and add a time delay with these statements:
pokesid + 4,17: pokesid + 11,17:remenabletones
for i = 1 to 50:next:rem time delay
4) Turn off the tones and add a time delay with the following
statements:
pokesid + 4,16:pokesid + 11,16:remdialtones
for i = 1 to 50:next:rem time delay
5) Now repeat steps 2 through 4 for each digit in the telephone num-
beryouaredialing.
6) Finally, disable the sound chip with this statement:
pokesid + 24,0
Note: The VIC 20 cannot simulate these tones with enough accu­
racy, so use rotary dialing with the VIC 20.
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