Specifications

ISI3334/4 Hardware/Driver Installation Manual

Appendix C - Tone Dial Frequencies

Hz Digits

697

770

852

941

Hz 1209 1336 1477 1633

1 2 3 A

4 5 6 B

7 8 9 C

0 # D

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%.

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.