9

4872A–CORD–08/05

U4091BM-R

9.

DTMF Dialing

The DTMF generator sends a multi-frequency signal through the matrix to the line. The signal is

the result of the sum of two frequencies and is internally filtered. The frequencies are chosen

from a low and a high frequency group. The circuit conforms to the CEPT recommendation con-

cerning DTMF option. Three different levels for the low level group and two different pre-

emphasis (2.5 dB and 3.5 dB) can be chosen by means of the serial bus (rec. T/CF 46-03).

Attention: In high gain mode, distortion can occur if AGATX is high and DC mask is low.

10. Melody and Confidence Tone Generation

Melody and confidence tone frequencies are given in Table 10-1.

The frequencies are provided at the DTMF input of the switch matrix. A sinusoidal wave, a

square wave or a pulsed wave can be selected by the serial bus. A square signal means the out-

put is high for half of the frequency cycle, and low for the other half. A pulsed signal means high

impedance phases of 1/6 of the period occur between the high and low phases.

Table 10-1.

Status of Melody Generating

Decimal

DTMFM[0:2]

Status

0

000

DTMF generator OFF

1

001

Confidence tone melody on (sine)

2

010

Ringer melody (pulse)

3

011

Ringer melody (square signal)

4

100

DTMF (mid level)

5

101

DTMF (low level)

6

110

DTMF (high level)

7

111

–

Table 10-2.

DTMF Frequencies

Decimal

DTMFF[0:1]

in DTMF Mode

Frequency

Error (%)

0

00

697

–0.007

1

01

770

–0.156

2

10

852

0.032

3

11

941

0.316

Table 10-3.

DTMF Frequencies

Decimal

DTMFF[2:3]

in DTMF Mode

Frequency

Error (%)

0

00

1209

–0.110

1

01

1336

0.123

2

10

1477

–0.020

3

11

1633

–0.182