136
MINI-MODEM (56 KBPS DATA/FAX MODEM)
Appendix A: 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 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%.
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
