The DS3141/DS3142/DS3143/DS3144 devices include all necessary circuitry to frame and format up to four separate DS3 or E3 channels. Each framer in these devices is independently configurable to support M23 DS3, C-Bit Parity DS3, or G.751 E3. The framers interface to a variety of line interface units (LIUs), microprocessor buses, and other system components without glue logic. Each DS3/E3 framer has its own HDLC controller, FEAC controller, and BERT, as well as full support for error detection and generation, performance monitoring, and loopbacks.