View ds21q43a datasheet:

DS21Q43A Quad E1 Framer www.dalsemi.com FEATURES FUNCTIONAL DIAGRAM Four E1 (CEPT or PCM-30) /ISDN-PRI framing transceivers All four framers are fully independent; RECEIVE ELASTIC transmit and receive sections of each framer FRAMER STORE are fully independent Frames to FAS, CAS, CCS, and CRC4 formats TRANSMIT ELASTIC FORMATTER STORE 8-bit parallel control port that can be connected to either multiplexed or non- multiplexed buses FRAMER #0 Each of the four framers contains dual two- FRAMER #1 frame elastic stores that can connect to FRAMER #2 asynchronous or synchronous backplanes up to 8.192 MHz FRAMER #3 Easy access to Si and Sa bits CONTROL PORT Extracts and inserts CAS signaling Large counters for bipolar and code violations, CRC4 code word errors, FA