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B Dial Pulses and Tones
CommPlete Communications Server 57
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 {xe "pulse ratios, setting"}{xe "Set
Pulse Dial Ratios command"}{xe "AT commands:&P"}&P command.
Closed
Open
Digit 2 Digit 1
A
B
Figure 2. Dial pulses
Tone Dial Frequencies
The {xe "tone dialing"}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 ({xe "DTMF (dual tone multifrequency):frequencies"}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
±
0.02%.
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.