74VHC943 is a full duplex low speed modem for data communication over telephone lines and other narrow bandwidth channels. It provides a 300 baud bidirectional serial interface and is Bell 103 compatible. The 74VHC943 utilizes advanced silicon-gate CMOS technology. Switched capacitor techniques are used to perform analog signal processing. The modulator section contains a frequency synthesizer and a sine wave synthesizer, producing a phase coherent frequency shift keyed (FSK) output. The line driver and hybrid section are designed to facilitate connection to a 600X telephone line, they can perform two to four wire conversion and drive the line at a maximum of b9 dBm. The demodulator section 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.