HFC-S2M Cologne Chip AG, HFC-S2M Datasheet - Page 209

• Manufacturer Part Number: HFC-S2M
• Description: Isdn HDLC Fifo Controller With Primary Rate Interface
• Manufacturer: Cologne Chip AG

value V_DTMF1 in the register R_DTMF1. A good compromise between bandwith of the
Goerzel filter and the length of the investigation is a value of 102. A DTMF detection can
be done on a continuous base. However 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-E1. After this, a new calculation can be started. However
some PCM samples (
The host processor should read the two
quencies for the desired channels. The coefficients are located in the SRAM memory of
HFC-E1. The memory address is calculated by
The individual address components are shown in Table 9.4.
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 equa-
tion (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
maximum 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-E1
( : These frequencies are modified to achieve a better detection compared with the high fundamental tones.)
Ö ××
×
Ü
values) can be lost.
Table 9.3: 16-bit
Ö ×× · Ö ÕÙ Ò Ý Ó«× Ø ·
1209
1336
1477
1633
697
770
852
941
ÀÞ Ã
1
×Ø
harmonic
27 980
26 956
25 701
24 219
19 073
16 325
13 085
DTMF controller
9 315
¡
Ã
×Ø
¾
Data Sheet
½
Ï
factors for the DTMF calculation
and 2
Æ
and
Ò
1406
1555
1704
1882
2418
2672
2954
3266
2
harmonic) can be detected.
ÀÞ Ã
Ò
Ï
Æ
harmonic
ÒÒ Ð Ó«× Ø ·
½
-10 565
-16 503
-22 318
-27 472
16-bit coefficients for 8 or 16 fre-
14 739
11 221
7 549
3 032
¡
¾
½
W-byte
Ó«× Ø
Cologne
Chip
209 of 272
(9.3)