PRELIMINARY
October 1995
74VHC943
300 Baud Modem (5V Supply)
General Description
Features
Y
5V supply
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.
Y
b
Drives 600X at 9 dBm
Y
Y
All filters on chip
Transmit level adjustment compatible with universal
service order code
The 74VHC943 utilizes advanced silicon-gate CMOS tech-
nology. Switched capacitor techniques are used to perform
analog signal processing.
Y
Y
Y
Y
Y
Y
Y
TTL and CMOS compatible logic
All inputs protected against static damage
Low power consumption
MODULATOR SECTION
Full duplex answer or originate operation
Analog loopback for self test
The modulator contains a frequency synthesizer and a sine
wave synthesizer. It produces a phase coherent frequency
shift keyed (FSK) output.
Power down mode
Direct Pin and function replacement for the 74HC943
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
b
conversion and drive the line at a maximum of 9 dBm.
Applications
Y
Built-in low speed modems
Y
Remote data collection
DEMODULATOR SECTION
Y
Radio telemetry
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.
Y
Credit verification
Y
Stand-alone modems
Y
Point-of-sale terminals
Y
Tone signaling systems
Y
Remote process control
Commercial
74VHC943WM
74VHC943N
Package Number
M20B
Package Description
20-Lead Molded JEDEC SOIC (0.300 Wide)
×
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
TL/F/11679–1
TRI-STATEÉ is a registered trademark of National Semiconductor Corporation.
C
1995 National Semiconductor Corporation
TL/F/11679
RRD-B30M125/Printed in U. S. A.