View ds21q44 datasheet:

DS21Q44 Enhanced QUAD E1 FRAMER www.dalsemi.com FEATURES FUNCTIONAL DIAGRAM Four E1 (CEPT or PCM-30) /ISDN-PRI framing transceivers Receive Elastic All four framers are fully independent; Framer Store transmit and receive sections of each framer Elastic Transmit are fully independent Store Formatter Frames to FAS, CAS, CCS, and CRC4 formats FRAMER #0 Each of the four framers contain dual two– FRAMER #1 frame elastic store slip buffers that can FRAMER #2 FRAMER #3 connect to asynchronous backplanes up to 8.192 MHz Control Port 8–bit parallel control port that can be used directly on either multiplexed or non– multiplexed buses (Intel or Motorola) Easy access to Si and Sa bits ACTUAL SIZE Extracts and inserts CAS signaling Large counters for bipolar and