HFC-4S Cologne Chip AG, HFC-4S Datasheet - Page 205

• Manufacturer Part Number: HFC-4S
• Description: Isdn HDLC Fifo Controller With 8 (4) Integrated S/t Interfaces
• Manufacturer: Cologne Chip AG

then the reading of the calculated coefficients has to be done in a very short time intervall before the
coefficients are cleared to zero for a new calculation. Is more convenient to set the V_DTMF_STOP
bit of the register R_DTMF0. The DTMF engine is stopped then after each calculation of a set of
coefficients and the V_DTMF_IRQ bit is set in the register R_IRQ_MISC. Then a software routine
has time to read the coefficients out of HFC-4S / 8S. After this, a new calculation can be started.
However some PCM samples (
The host processor should read the two
for the desired channels. The coefficients are located in the SRAM memory of HFC-4S / 8S. The
memory address is calculated by
The individual address components are shown in Table9.4.
If 32 channels are used, only the 8 fundamental frequencies can be detected. If only 16 channels are
used, all 16 frequencies (1
For every frequency and every channel the power amplitude can be calculated with equation ( 9 .2).
This calculation is not implemented in the chip and has to take place in the host processor.
After a discrimination process and a balance check between 2 frequency candidates with the maxi-
mum power, the software can determine if there was a DTMF signal on the line or not. If there was a
DTMF signal the tone pair is detected and so the dialed digit is decoded.
In case the existence of DTMF tones in an arbitrary voice signal has to be detected, it is helpfull to
investigate not only the 8 DTMF tones but also their second harmonics. For DTMF tones the second
harmonics should have no significant amplitude.
March 2003 (rev. A)
HFC-4S
HFC-8S
( : These frequencies are modified to achieve a better detection compared with the high fundamental tones.)
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Table 9.3: 16-bit
and 2
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Ü
1209
1336
1477
1633
values) can be lost.
697
770
852
941
ÀÞ Ã
1
Ò
×Ø
harmonic) can be detected.
harmonic
27 980
26 956
25 701
24 219
19 073
16 325
13 085
DTMF controller
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9 315
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Æ
Data Sheet
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factors for the DTMF calculation
and
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Æ
1406
1555
1704
1882
2418
2672
2954
3266
2
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Ò
½
harmonic
16-bit coefficients for 8 or 16 frequencies
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-10 565
-16 503
-22 318
-27 472
14 739
11 221
7 549
3 032
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W-byte
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Cologne
Chip
205 of 273
(9.3)