Call Progress Tone Generation
Call progress tones are audible tones sent from
switching systems to calling parties (or equipment) to
indicate the status of calls. Calling parties can identify
the success of a placed call by what is heard after dial-
ing. The M-991 series utilizes a highly linear tone gen-
erator that produces the unique frequencies (singly or
in pairs) that are common to call progress signals.
Duration and frequency selection are digitally con-
trolled (see the Data/Tone Selection table below for
data settings for a particular tone output). A typical
control sequence for the M-991 is: (1) set data lines to
desired frequency selection, (2) wait for data lines to
settle, (3) drive the chip enable (CE) low, (4) maintain
CE low for desired tone duration (Note: data lines may
be changed after data hold time), and (4) return CE to
a logic high. (Commonly used call progress tones are
shown in the Data/Tone Selection table below.) In a
bus-oriented system, noise on the data lines may
propagate through the device and appear at the out-
put. To safeguard against this, use an external latch to
lock the data into the device. In addition, it is good
practice to bypass the VREF pin to ground with a small
capacitor (0.01 mF) to reduce power supply noise. The
designer should be aware of device timing require-
ments and design accordingly. The data input pins
may be tied high (+5 VDC) or low (ground) as required,
but D4 and D5 must be left open. Beware of hardwiring
the CE pin for dedicated tone generation. This input is
edge triggered. An RC network like that shown in the
Power-on Reset Circuit on Page 4 should be used to
momentarily reset the device immediately following
power-up to ensure proper operation.
D0 D1 D2 D3 Frequency (Hz)
0 0 0 0 350
440 Dial Tone
0 0 0 1 400
0 0 1 0 440
off Alert Tone
0 0 1 1 440
480 Audible Ring
0 1 0 0 440
0 1 0 1 480
off Bell high tone
0 1 1 0 480
620 Reorder(Bell low)
0 1 1 1 350
1 0 0 0 620
1 0 0 1 941
1209 DTMF “*”
Standard Call Progress Tones
D0 - D3
Latches data and enables output (active
Data input pins. (See Data/Tone Selection.)
Output indicates that a signal is being generated at
Linear buffered tone output.
Most positive power supply input pin.
Internally generated mid-power supply voltage
Most negative power supply input pin.
Crystal oscillator or digital clock input.
Crystal oscillator output.
Repeat, tones on and off 250 ms ± 25 ms each.
Repeat, tones on and off 500 ms ± 50 ms each.
Reat, tones on 2 ± 0.2 s, tones off 4 ± 0.4 s
Three bursts tones on and off 100 ms ± 20 ms each followed by dial tone.
Tones on 1 ± 0.2s, followed by single 440 Hz on for 0.2s on, and silence for 3 ±
0.3 s, repeat.
Repeat alternating tones, each on for 230 ms ± 70 ms with total cycle of 500 ±
One burst 200 ± 100 ms
One burst of tone on 1.75 ± 0.25 s before attendant intrudes, followed by burst
of tone 0.65 ± 0.15 s on, 8 to 20 s apart for as long as the call lasts
One burst of tone for 3 ± 1 s before overriding station intrudes
Three bursts on and off 100 ms each or 100 ms on, 100 ms off, 300 ms on
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