TS7514 datasheet(4/19 Pages) STMICROELECTRONICS

4 / 19 page

FUNCTIONAL DESCRIPTION

The TS7514 circuit is an FSK modem for half-du-

plex, voice-band asynchronoustransmissions on a

2-wire line according to CCITT recommendation

V.23 or full duplex on 4 wire-line.

The circuit features DTMF dialing, call status tone

detection and line monitoring in both dialing and

automaticanswer modes. A signalling frequency is

available at the line monitoring output (buzzer).

Ring detection is possible by using the signal de-

tection function and bypassing the receive filter.

The receive signal at ZCO output can be filtered in

the associated microprocessor.

The TRANSMIT channel (Tx) includes :

- Two programmable frequency generators.

- One switched capacitor filter (SCF) with low-pass

or bandpass configuration and its associated

propagation delay corrector.

- One continuous time low-pass smoothing filter.

- One attenuator, programmable from 0 to + 13dB

by 1dB steps.

- One programmable analog input.

The RECEIVE channel (Rx) includes :

- Two operational amplifiers for duplexer imple-

mentation.

- One continuous time low-pass anti-aliasing filter.

- One programmable gain amplifier.

- One linear compromise equalizer.

- One switched capacitor band pass filter (can be

set to either main or back channel).

- One continuous time low pass smoothing filter.

- One limiting amplifier.

- One correlation demodulator.

- One programmable level signal detector.

The LINE MONITORING channel includes :

- One buzzer.

- One 3-channel multiplexer to select beetwen :

- Transmit channel monitoring.

- Receive channel monitoring.

- Buzzer.

- One programmable attenuator

Internal Control

Power-up Initialization

The TS7514includes power-up initialization of con-

trol registers. This system sets the ATO transmis-

sion output to an infinite attenuation position,

leaving time for the microprocessor to set up the

RPROG input on power up. Control registers are

also initialized when V+ is lower than 3V or V-

greater than -3V.

Registers

Writeaccess to the DTMF data registerand to other

control registers is achieved in serial mode through

TxD input or PRD input. Addressing of these 4 bit

registers is indirect. They are accessed through an

8 bit shift register addressed when MOD/DTMF = 0

and MC/BC = 0. Data sent to the TxD input is

strobed on the RTS signal trailing edge.

Serial data is sent to the TxD input, with Least

Significant Bit (LSB) first. The 4 Most Significant

Bits (MSB) contain the control register address

while the 4 LSB contain associated data.

Data transfer from the input register to the control

operating mode (MODEM or DTMF) selection

(MOD/DTMF = 1 or MC/BC = 1).

MOD/DTMF

MC/BC

RTS

TxD or PRD

Data

Address

Time

RPROG

RDTMF

RATTE

RWLO

RPTF

RHDL

RPRX

RPROG

TxD or

PRD

RTS

CLK

Datas

Addresses

8-BIT SHIFT REGISTER

(Input Register)

4-Bit Control

Figure 2 : Internal Control Register

TS7514

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