HFC-S2M Cologne Chip AG, HFC-S2M Datasheet - Page 208

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

HFC-E1
9.1 DTMF detection engine
The transmission of dialed numbers on analog lines is normaly done by DTMF (Dual Tone
Multi-Frequency). This means that pairs of two frequencies are used to determine one key
of a keypad like shown in Table 9.2.
Thus there are 4 low tones and 4 high tones and therefore 16 combinations of 2 tones. Be-
cause the ISDN network has several interfaces to the old-fashioned POTS analog network,
in-band number dialing with DTMF can take place. To decode this DTMF information the
HFC-E1 has a built in DTMF detection engine.
The detection is done by the digital processing of the PCM input data by the so-called Go-
erzel Algorithm
where
factor
is a constant for each frequency and
calculated every 125 s for 16 or 32
The start condition is
After processing equation (9.1) for
The calculation of equation (9.1) is done for every new PCM sample value (for all 8 fre-
quencies) every 125 s. Optionally also the second harmonic (double frequency) is also
investigated. The
calculation is implemented in integer arithmetic, it is useful to multiply
the whole 16 bit value range. These
The DTMF engine must be enabled by setting bit V_DTMF_EN in register R_DTMF0.
How many iterations are calculated with the Goerzel algorithm is determined by the register
208 of 272
Ï
Ò
·½
is a coefficient calculated from the 2 previous coefficients
Ã
factors are values concerning to the DTMF frequencies. If the DTMF
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1209
¼
1
4
7
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Table 9.2: DTMF tones on a 16 keys keypad
¾
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1336
2
5
8
0
½
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à ¾ Ó× ¾
Ò
Keypad
·½
Æ
¾
Æ
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¼
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· Ï
1477
Ü
DTMF controller
.
times the real power amplitude is
3
6
9
#
Ò
values are listed in Table 9.3.
Ã
is a new PCM value every 125 s. Equation (9.1) is
·½
Data Sheet
Æ
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values.
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1633
½
A
B
C
D
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high tones (
Frequencies
697
770
852
941
¼¼¼ ÀÞ
¡
Ò
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½
Æ
· Ü
¡
low tones
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(
Æ
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ÀÞ )
½
Ã
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March 2003 (rev. A)
with
Ò
and
¾
½
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Cologne
Chip
to exploit
Ò
½
. The
(9.1)
(9.2)