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PCD3312C

DTMF/modem/musical-tone generators

Philips Electronics 

Philips Semiconductors

DTMF/modem/musical-tone generators

Product specification

PCD3311C; PCD3312C

7 FUNCTIONAL DESCRIPTION

7.1 General (see Fig.1)

The Input Control Logic decodes the input data to

determine whether DTMF, modem or musical tones are

selected; and which particular tone or combination of

tones is required.

A code representing the required tones is sent to the

Divider Selection ROM which selects the correct division

ratio in both of the Frequency Dividers (or in one divider, if

only a single tone is required).

The Oscillator circuit provides a square wave of frequency

3.58 MHz. Each Frequency Divider divides the frequency

of the Oscillator to give a serial digital square wave with a

frequency simply related to that of the required tone.

The output from each Frequency Divider goes to a DAC,

which is also fed by a clock derived from the oscillator.

Using these two signals, the DAC produces an

approximate sine wave of the required frequency, with an

amplitude derived from the Voltage Reference.

The output from the DAC goes to an Adder where, for

DTMF, it is combined with the output from the other DAC.

The output from the Adder goes through two stages of Low

Pass Filters to give a smoothed tone (single or dual), and

finally to the TONE output.

7.4 Data inputs (PCD3311C)

Inputs D0, D1, D2, D3, D4 and D5 are used in the parallel

data input mode of the PCD3311C. Inputs D0 and D1 are

also used in serial input mode when they act as the SCL

and SDA inputs respectively. Inputs D0 and D1 have no

internal pull-down or pull-up resistors and must not be left

open in any application. Inputs D2, D3, D4 and D5 have

internal pull-down.

D4 and D5 are used to select between DTMF dual, DTMF

single, modem and musical tones (see Table 1). D0, D1,

D2 and D3 select the tone combination or single tone

within the selected application. They also, in combination

with D4, select the standby mode. See Tables 2, 3, 4

and 5.

PCD 3312C has no parallel data pins as data input is via

the I2C-bus.

Table 1 Use of D5 and D4 to select application

D5 D4

APPLICATION

LOW LOW DTMF single tones; musical tones;

standby

LOW HIGH DTMF dual tones (all 16 combinations)

HIGH LOW modem tones

HIGH HIGH musical tones

7.2 Clock/oscillator connection

The timebase for the PCD3311C and PCD3312C is a

crystal-controlled oscillator, requiring a 3.58 MHz quartz

crystal to be connected between OSCI and OSCO.

Alternatively, the OSCI input can be driven from an

external clock of 3.58 MHz.

7.3 Mode selection (PCD3311C)

The MODE input selects the data input mode for the

PCD3311C. When MODE is connected to VDD (HIGH),

data can be received in the parallel mode. When

connected to VSS (LOW) or left open, data can be received

via the serial I2C-bus.

PCD 3312C has no MODE input as data input is via the

I2C-bus only.

7.5 Strobe input (PCD3311C )

The STROBE input (with internal pull-down) allows the

loading of parallel data into D0 to D5 when MODE is HIGH.

The data inputs must be stable preceding the

positive-going edge of the strobe pulse (active HIGH).

Input data are loaded at the negative-going edge of the

strobe pulse and then the corresponding tone (or standby

mode) is provided at the TONE output. The output remains

unchanged until the negative-going edge of the next

STROBE pulse (for new data) is received. Figure 5 is an

example of the timing relationship between STROBE and

the data inputs.

When MODE is LOW, data is received serially via the

I2C-bus.

1996 Nov 21

6

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