MT9196
Data Sheet
The frequency of the low group tone is programmed by writing an 8-bit coefficient into the Low Tone Coefficient
Register (address 1Ah) while the high group tone frequency uses the 8-bit coefficient programmed into the High
Tone Coefficient Register (address 1Bh). Both coefficients are determined by the following equation:
Frequency (in Hz) = 7.8125 x COEFF
Where COEFF is an integer between 0 and 255. Frequency resolution is 7.8125 Hz in the range 0 to 1992 Hz.
Low and high tones are enabled individually via the LoEn and HiEN control bits (DTMF/Ringer Control Register,
address 18h). This not only provides control over dual tone generation but also allows single tone generation using
either of the enable bits and its associated coefficient register.
After programming and enabling the tone generators as described, selection of transmit and/or receive path
destinations are carried out via the Path Control Registers (see Path Control section). In addition receive sidetone
DTMF must be selected via the DTMF StEN bit (DTMF/Tone ringer Register, address 18h) so that it replaces the
received PCM in the Rx Filter path.
Frequency
(Hz)
697
770
852
941
1209
1336
1477
1633
Actual
Frequency
695.3
773.4
851.6
945.3
1210.9
1335.9
1476.6
1632.8
%
Deviation
-.20%
+.40%
-.05%
+.46%
+.20%
.00%
-.03%
-.01%
COEFF
59h
63h
6Dh
79h
9Bh
ABh
BDh
D1h
Table 2 - DTMF Frequencies
DTMF Signal to distortion:
The sum of harmonic and noise power in the frequency band from 50 Hz to 3500 Hz is typically more than 30 dB below the power in
the tone pair. All individual harmonics are typically more than 40 dB below the level of the low group tone.
Table 2 gives the standard DTMF frequencies, the coefficient required to generate the closest frequency, the actual
frequency generated and the percent deviation of the generated tone from the nominal.
Tone Ringer
A dual frequency squarewave ringing signal may be applied to the handsfree speaker driver to generate a call
alerting signal. To enable this mode the Ring En bit (address 18h) must be set as well as the ringer function to the
loudspeaker via the Receive Path Control Register (address 13h). Ring En is independent of the DTMF enable
control bits (see Lo EN and Hi EN). Since both functions use the same coefficient registers they are not usually
enabled simultaneously.
The digital tone generator uses the values programmed into the low and high Tone Coefficient Registers
(addresses 1Ah and 1Bh) to generate two different squarewave frequencies.
Both coefficients are determined by the following equation:
COEFF = [32000/Frequency (Hz)] - 1
where COEFF is an integer between 1 and 255. This produces frequencies between 125 - 16000 Hz with a non-
linear resolution.
The ringer program switches between these two frequencies at a 5 Hz or 10 Hz rate as selected by the WR bit in
the DTMF/Tone ringer register (address 18h).
7
Zarlink Semiconductor Inc.
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