MT88L89AC MITEL [Mitel Networks Corporation], MT88L89AC Datasheet - Page 7

• Manufacturer Part Number: MT88L89AC
• Description: 3V Integrated DTMFTransceiver with Adaptive Micro Interface
• Manufacturer: MITEL [Mitel Networks Corporation]

Advance Information
The period of each tone consists of 32 equal time
segments. The period of a tone is controlled by
varying the length of these time segments. During
write operations to the Transmit Data Register the 4
bit data on the bus is latched and converted to 2 of 8
coding for use by the programmable divider circuitry.
This code is used to specify a time segment length,
which will ultimately determine the frequency of the
tone. When the divider reaches the appropriate
count, as determined by the input code, a reset pulse
is issued and the counter starts again. The number
of time segments is fixed at 32, however, by varying
the
frequency can also be varied. The divider output
clocks
sinewave lookup ROM.
The lookup table contains codes which are used by
the switched capacitor D/A converter to obtain
discrete and highly accurate DC voltage levels. Two
identical circuits are employed to produce row
column tones, which are then mixed using a low
noise summing amplifier. The oscillator described
needs no “start-up” time as in other DTMF
generators since the crystal oscillator is running
continuously thus providing a high degree of tone
burst
incorporated and serves to attenuate distortion
products above 8 kHz. It can be seen from Figure 6
that the distortion products are very low in amplitude.
Burst Mode
In certain telephony applications it is required that
DTMF signals being generated are of a specific
duration
segment length
accuracy.
another
determined
counter,
A bandwidth
as described
either
which
by
limiting
addresses
the
above
particular
Figure 10 - Spectrum Plot
filter is
and
the
the
application or by any one of the exchange transmitter
specifications currently existing. Standard DTMF
signal timing can be accomplished by making use of
the Burst Mode. The transmitter is capable of issuing
symmetric bursts/pauses of predetermined duration.
This burst/pause duration is 51 ms±1 ms which is a
standard interval for autodialer and central office
applications. After the burst/pause has been issued,
the appropriate bit is set in the Status Register
indicating that the transmitter is ready for more data.
The timing described above is available when DTMF
mode has been selected. However, when CP mode
(Call Progress mode) is selected, the burst/pause
duration is doubled to 102 ms ±2 ms. Note that when
CP mode and Burst mode have been selected,
DTMF tones may be transmitted only and not
received. In applications where a non-standard
burst/pause time is desirable, a software timing loop
or external timer can be used to provide the timing
pulses when the burst mode is disabled by enabling
and disabling the transmitter.
Single Tone Generation
A single tone mode is available whereby individual
tones from the low group or high group can be
generated. This mode can be used for DTMF test
equipment
generation and distortion measurements. Refer to
Control Register B description for details.
Scaling Information
10 dB/Div
Start Frequency = 0 Hz
Stop Frequency = 3400 Hz
Marker Frequency = 697 Hz and
1209 Hz
applications,
acknowledgment
MT88L89
tone
4-131