XR-2121

XR-2121 Bell 2 12A Type Modulator GENERAL DESCRIPTION The, XR-2121 is designed to provide the complete modulator function for a Bell 212A type modem. The circuit accepts a synchronous serial data stream and generates either a 300 BPS frequency shift keyed (FSK) or a 1200 BPS differential phase shift keyed (DPSK) carrier signal. An on-board digital-to-analog converter provides a synthesized sine wave output. Also provided on the transmitted carrier output is an inverting amplifier with external feedback resistor to provide a carrier amplitude adjust. The XR-2121 contains an internal 17 bit scrambler. This scrambler which is used during DPSK operation has a disable input for sending non-scrambled carriers. A 1200 Hz transmit clock output is provided for 1200 BPS operation, although the XR-2121 will also accept an external transmit clock. For test or other purposes, a 600 Hz baud clock output is also supplied. The XR-2121 is constructed using silicon gate CMOS technology. The main c...