ST75C540 datasheet(13/84 Pages) STMICROELECTRONICS

13 / 84 page

V - FUNCTIONAL DESCRIPTION

V.1 - System Architecture

The chip allows the design of a complete FAX, Data

Modem, Hands-Free Telephone and Answering

Machine system. A versatile dual port RAM allows

an easy interface with most micro-controllers.

V.2 - Modes of Operation

Refer to Appendix A for Block Diagrams.

V.3 - Operations

V.3.1 - Modem Transmitter Description

The signal pulses are shaped in a dedicated filter

further combined with a compromise transmit

equalizer suited for transmission over strongly dis-

torted lines. 3 different compromise equalizers are

available and can be selected by software.

V.3.2 - Modem Receiver Description

The receiver section handles complex signals and

uses a fractionally spaced complex equalizer. It is

able to cope with distant modem timing drifts up to

-4 as specified in the ITU-T recommendations.It

also compensates for frequency drift up to 10Hz

and for phase jitter at multiple and simultaneous

frequencies.

V.3.3 - Tone Generator Description

Four tones can be simultaneouslygeneratedby the

ST75C530/540. These tones are determined by

their frequenciesand by the output amplitude level.

A set of specific commands are also available for

DTMF generation. Any of the4 tonegeneratorscan

be output independently either on the Audio DAC

or the line DAC.

V.3.4 - Tone Detector Description

During TONE (respectively TONECID) Mode six-

teen (respectively eight) tones can be simultane-

ously detected by the ST75C530/540. Each of the

tones to be detected is defined by the coefficients

of a 4th order programmable IIR. Detection thresh-

olds are programmable from -51dBm up to -6dBm.

These primary detectors can detect tone up to

3.3kHz (sampling rate 7.2kHz in all modes). They

also have a programmable internal wiring feature

(see Chapter IX).

In all modes, except Handset (HANDSET) and Full

Duplex V.3 2bis/V.3 2/V.22bis/V.22 (Modem)

modes, 4 additional tone detectors (each of them

being a 4th order programmable IIR) are concur-

rently running. In Handset mode only 2 additional

tone detectors are available. Detection thresholds

are programmable from -51dBm up to -6dBm. This

secondary programmable detector can detect

tones up to 1.8kHz by default set-up with a sam-

pling rate at 4.8kHz. But this 4 additional tone

detectors can also detect tones up to 3.3kHz with

a sampling rate at 9.6kHz. In order to avoid wrong

detectgion, relative detectgion is also provided.

V.3.5 - V.21 Channel 2 Flag Detector Description

In all the Receive FAX Modes, including V.21 Chan-

nel 2 Mode, the ST75C530/540 processes a V.21

Flag “7E” detector, either in the idle state, the train

sequence or the data mode. The detection time is

3 consecutive flags to detect and 1 byte to loose

the detection.

V.3.6 - HDLC Description

In all FAX Modes (MODEM), including V.21 Chan-

ne l

Mo d e,

and

al s o

F u ll

D uplex

V.32bis/V.32/V.22bis/V.22 (Modem) modes, a

HDLC framing and deframing is supported by the

ST75C530/540. The number of transmitted flags

can be programmed.

V.3.7 - UART Description

In Full Duplex V.32bis/V.32/V.22bis/V.22 Modem

Modes and TONECID V.23receive mode, a parallel

UART is performed by the ST75C530/540. This

UART manage the Break signal either at the trans-

mit and the receive bit stream. The Data format

supported are 7 and 8 bit of Data; even, odd or no

Parity, 1 or 2 stop bits.

V.3.8 - DTMF Detector Description

ADTMF Detector is includedin the ST75C530/540,

it allows detection of valid DTMF Digits. A valid

DTMF Digit is defined as a dual tone with a total

power higher than -43dBm, a duration higher than

40ms and a differentialamplitude within

±8dB. This

DTMF Detector is enabled in all modes except in

Fax Modem, Data Modem and Handset modes. It

is also enabled in V.21 Channel 2 Receive Mode.

The DTMF thresholds and duration can be

changed from they default value by overwriting

DSP’s RAM locations. In the default setup, this

detector is compliant with the NET4 standard. The

frequencydeviation can be changedby overwriting

the default DTMF’s filters coefficients.

V.3.9 - Ring Detector

This detector detects RING signal from 15Hz to

68Hz, it can be programmed to expand the mini-

mum and maximum detection frequency up to

12Hz (for min) and 144Hz (for max). The detection

time is equal to one period of the ring signal, and

the loose time to the minimum between one period

of the ring signal and the inverse of the minimum

frequency.

The associated STA_RING status is as Figure 1.

ST75C530 - ST75C540

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