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Appendix B
Dial Pulse and Tone-Dial Frequencies
DIAL PULSES
B
Closed
A
Open
Digit 2
Digit 1
In the example above, the digit 2 is pulse dialed, followed by the digit 1. Each pulse consists of an A
mSec. open and a B mSec. closed, where A will be either 60 or 67 mSec and B will be either 40 or 33
mSec., for a total of 100 mSec. per pulse, or a rate of 10 pulses per second. The interdigital pause time is
800 mSec. The pulse ratios are controlled by the &P command*.
TONE DIAL FREQUENCIES
Hz
Digits
697
770
852
941
Hz
1209
1336
1477
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 the four low frequencies (697, 770, 852, 941 Hz),
while the three vertical columns use the three high frequencies (1209, 1336, 1477 Hz). The generally
accepted tone frequency tolerance is +0.02%.
*Not applicable in BABT models
For example, the digit 4 would be dialed by combining two tone frequencies. It would use the frequency
770 Hz from the second row, and the frequency 1209 Hz from the first column. In another example, the
digit 9 would be dialed with the tone frequencies of 852 Hz and 1477 Hz.
The extended DTMF characters (A, B, C, D) are the high-end frequencies (1633 Hz) defined on some
telephone sets with a fourth vertical column of buttons. This fourth column provides for extended PBX
control functions; the actual functions provided are dependent on the PBX manaufacturer’s
implementation and feature set.
Hz
Digits
697
1
2
3
A
770
4
5
6
B
852
7
8
9
C
941
*
0
#
D
Hz 1209 1336 1477
1633