MM74HC942 300 Baud Modem General Description The MM74HC942 is a full duplex low speed modem. It provides a 300 baud bidirectional serial interface for data communication over telephone lines and other narrow bandwidth channels. It is Bell 103 compatible. The MM74HC942 utilizes advanced silicon-gate CMOS technology. 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 connection to a 600X phone line. They can perform two-to-fourwire conversion and drive the line at a maximum of 0 dBm. 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 Drives 600X at 0 dBm 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 g5V supplies Y Low power consumption Y Full duplex answer or originate operation Y Analog loopback for self test Y Power down mode