The framer interfaces to a 2.048 Mbit/s backplane providing selectable data link access with optional HDLC controllers for either the FDL bits and channel 24 (T1 mode) or Sa bits and channel 16 (E1 mode). The LIU interfaces the framer to T1 (T1 mode) or PCM 30 (E1 mode) transformer-isolated four-wire line with minimal external components required. In T1 mode the MT9074 supports D4, ESF and SLC96 formats, meeting the latest recommendations including ITU I.431, AT&T PUB43801, TR-62411, ANSI T1.102, T1.403 and T1.408. In E1 mode the MT9074