The CMX635 is an integrated Subscriber Processor designed for low chip-count ISDN voice/data terminals and POTS terminal adaptors. Its functions facilitate operation in an ISDN feature phone with speakerphone capability or in a POTS terminal adapter with Subscriber Pulse Metering (SPM), DTMF encoder/decoder, Caller Line ID (CLID) and Caller ID on Call Waiting (CIDCW) capabilities. It also implements many functions needed in an intelligent NT or NT1Plus system. The CMX635 incorporates a 4-wire ST interface conforming to ITU-T I.430 and ETS 300 012-1 specifications. HDLC Controllers and associated FIFOs are provided for B1, B2 and D-channels, which can be configured to automatically process the bit stuffing, flag generation/recognition, address matching and CRC generation/checking required to support the ITU Q.921 protocol. An TM