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Appendix B Dial Pulses and Tones
Dial Pulses
When you pulse dial, as when you make a call with a rotary dial telephone, your telephone or modem
generates codes in the form of pulses that simulate the opening and closing of old-fashioned electric
relays, or switches. The number of pulses in a code are the same as the digit they encode; thus, the digit 1 is
represented by one pulse, the digit 2 by two pulses, etc. In Figure B-1, the digit 2 is pulse dialed, followed
by the digit 1 . Each pulse consists of an A ms open (break) and a B ms closed (make), where A is either 60
or 67 ms, and B is either 40 or 33 ms, for a total of 100 ms per cycle, or a rate of 10 pulses per second. The
interdigital pause time is 800 ms. The pulse ratios are controlled by the &P command.
Closed
Open
Figure 2. Dial pulses
Tone Dial Frequencies
The tone dialing method combines two frequencies for each of the twelve digits found on a touch-tone dial
pad. This method is referred to as dual-tone multi-frequency (DTMF) dialing.
The four horizontal rows on a touch-tone keypad use four low-frequency tones (697, 770, 852, 941 Hz),
while the three vertical columns use three high-frequency tones (1209, 1336, 1477 Hz). The tone frequency
tolerance is
For example, the digit 4 is dialed by combining two tone frequencies: 770 Hz from the second row, and
1209 Hz from the first column. In another example, the digit 9 is dialed with tone frequencies 852 Hz and
1477 Hz.
Hz
697
770
852
941
Hz
CommPlete Communications Server
B
A
Digit 2
±
0.02%.
Digits
1
2
3
4
5
6
7
8
9
*
0
#
1209
1336
1477
B Dial Pulses and Tones
Digit 1
43
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