TLF11679

PRELIMINARY

October 1995

74VHC943

300 Baud Modem (5V Supply)

General Description

The 74VHC943 is a full duplex low speed modem It pro-

vides a 300 baud bidirectional serial interface for data com-

munication over telephone lines and other narrow band-

width channels It is Bell 103 compatible

The 74VHC943 utilizes advanced silicon-gate CMOS tech-

nology Switched capacitor techniques are used to perform

analog signal processing

MODULATOR SECTION

The modulator contains a frequency synthesizer and a sine

wave synthesizer It produces a phase coherent frequency

shift keyed (FSK) output

LINE DRIVER AND HYBRID SECTION

The line driver and hybrid are designed to facilitate connec-

tion to a 600X phone line They can perform two to four wire

DEMODULATOR SECTION

The demodulator incorporates anti-aliasing filters a receive

filter limiter discriminator and carrier detect circuit The

nine-pole receive filter provides 60 dB of transmitted tone

rejection The discriminator is fully balanced for stable

operation

Features

Y

5V supply

Y

Y

All filters on chip

Y

Transmit level adjustment compatible with universal

service order code

Y

TTL and CMOS compatible logic

Y

All inputs protected against static damage

Y

Low power consumption

Y

Full duplex answer or originate operation

Y

Analog loopback for self test

Y

Power down mode

Y

Direct Pin and function replacement for the 74HC943

Applications

Y

Built-in low speed modems

Y

Remote data collection

Y

Radio telemetry

Y

Credit verification

Y

Stand-alone modems

Y

Point-of-sale terminals

Y

Tone signaling systems

Y

Remote process control

Commercial

Package Number

Package Description

74VHC943WM

M20B

20-Lead Molded JEDEC SOIC (0300 Wide)

74VHC943N

N20A

20-Lead Molded DIP

Note

Surface mount packages are also available on Tape and Reel Specify by appending the suffix letter

‘‘X’’ to the ordering code

Connection Diagram

Pin Assignments for

SOIC and PDIP

TLF11679 – 1

TRI-STATE

is a registered trademark of National Semiconductor Corporation

C1995 National Semiconductor Corporation

RRD-B30M125Printed in U S A