The LXT6234 E-Rate Multiplexer is a single-chip solution for multiplexing four tributary channels into a single high speed data stream and for demultiplexing a high speed data stream back to four tributary channels. All of the necessary circuitry is integrated into the LXT6234 ERate Multiplexer; there is no need for an external framing device. The LXT6234 E-Rate Multiplexer conforms to both the (ITU) G.742 and (ITU) G.751 multiplexing formats defined by the International Telecommunications Union (ITU; formerly known as CCITT): G.742 recommendation for multiplexing four E1 channels into an E2 frame; and the G.751 recommendation for multiplexing four E2 channels into an E3 frame. The LXT6234 E-Rate Multiplexer also encodes and decodes HDB3 zero suppression line coding used on E1, E2, and E3 signals. The coder and decoder input/output pins are externally accessible, allowing either HDB3 or NRZ (non-return-to-zero) I/O to the multiplexer. The LXT6234 E-Rate Multiplexer can also serve as a five channel HDB3 coder and decoder.