MultiModemISI Hybrid Series, ISIHI-2S 151
Appendix
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 that are
provided depend on the PBX manufacturer’s implementation and feature set.
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
*