The DS21Q55 is a quad software-selectable T1, E1, or J1 MCM device for short-haul and long-haul applications. Each port is composed of a line interface unit (LIU), framer, HDLC controllers, and a TDM backplane interface, and is controlled by an 8-bit parallel port configured for Intel or Motorola bus operations. The DS21Q55 is software compatible with the DS2155 single-chip transceiver. It is pin compatible with the DS21Qx5y family of products. Applications * Channel Banks * Channel Service Units (CSUs) * Data Service Units (DSUs) * DSL Add/Drop Multiplexers * Muxes * Routers/Switches * Routers/Switches * T1/E1 Test Equipment * Complete T1/DS1/ISDN-PRI/J1 Transceiver Functionality * Complete E1 (CEPT) PCM-30/ISDN-PRI Transceiver Functionality * Long-Haul and Short-Haul Line Interface for Clock/Data Recovery and Waveshaping * CMI Coder/Decoder for Optical I/F * Crystal-Less Jitter Attenuator * Fully Independent Transmit and Receive Functionality * Dual HDLC Controllers * Programmable BERT Generator and Detector * Internal Software-Selectable Receive and Transmit-Side Termination Resistors for 75Ω /100Ω /120Ω T1 and E1 Interfaces * Dual Two-Frame Elastic-Store Slip Buffers that Connect to Asynchronous Backplanes Up to 16.384MHz * 16.384MHz, 8.192MHz, 4.096MHz, or 2.048MHz Clock Output Synthesized to Recovered Network Clock