DUAL TONE MULTI FREQUENCY TONE TABLE
When a keypad button is pressed, the DTMF generator produces two tones, one below 1000Hz indicating the keypad row, the other above 1000Hz indicating the keypad column. The result is a combination of 16 possible tone products, each representing an alpha/numeric or symbol as shown in the following table.
1209 Hz |
1336 Hz |
1477 Hz |
1633 Hz |
||
Keypad |
Col (0) |
Col (1) |
Col (2) |
Col (3) |
|
697 Hz |
Row (0) |
1 |
2 |
3 |
A |
770 Hz |
Row (1) |
4 |
5 |
6 |
B |
852 Hz |
Row (2) |
7 |
8 |
9 |
C |
941 Hz |
Row (3) |
* |
0 |
# |
D |
Note that the standard telephone keypad does not include Col (3) - (symbols A, B, C & D).