DTMF Tone Generator
Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over analog paths.
The DTMF keypad is a 4x4 matrix in which each row represents a low frequency and each column represents a high frequency. Pressing a single key sends a sinusoidal tone for each of the two frequencies. Eg, key '1' produces a superimposition of tones of 697 and 1209 hertz (Hz).
| 1209Hz | 1336Hz | 1477Hz | 1633Hz | |
|---|---|---|---|---|
| 697Hz | ||||
| 770Hz | ||||
| 852Hz | ||||
| 941Hz |
ABCD Keys
The ABCD Keys maybe used for maintenance functions, or special features.
For example, the AutoVon (military) network used ABCD keys to identify precedence level:
- (FO) Flash Override (highest priority)
- (F) Flash
- (I) Immediate
- (P) Priority
With a Meridian PBX, each button (A, B, C, D, * and #) can have up to three functions assigned to it, determined by the mode of operation (pre-dial, post-dial or control mode). The functions can be either Flexible Feature Code functions or the autodial function. An autodial number (of up to 23 digits) can be assigned to any of these buttons for either the pre-dial or post-dial modes. In addition, an autodial number can be assigned to the recall (RCAL) button in the pre-dial mode. See LD 18 for more details.
A 16-Button DTMF phone can be used with a Meridian PBX when:
- 16-Button DTMF is enabled:
LD 17, PARM: ABCD = YES - An ABCD table is defined, and associated with a station group:
LD 18, TYPE: ABCD - All the Digitone Receivers (DTRs) have the correct strap settings.
Other tones:
| Dial Tone 350Hz and 450Hz | |
| Ringing Tone 400Hz and 450Hz (On for 400ms, off for 200ms) | |
| Busy Tone 400Hz (On for 350ms, off for 350ms) | |
| Number Not Recognised Tone 950Hz / 1400Hz / 1800Hz (Each tone for 330ms, with a 15ms pause between tones) |