The S5T8554B/7B are single-chip PCM encoders and decoders (PCM CODECs) and PCM line filters. These devices provide all the functions required to interface a full-duplex voice telephone circuit with a time-division-multiplex (TDM) system. These devices are designed to perform the transmit encoding and receive decoding as well as the transmit and receive filtering functions in PCM system. They are intended to be used at the analog termination of a PCM line or trunk. These devices provide the bandpass filtering of the analog signals prior to encoding and after decoding. These combination devices perform the encoding and decoding of voice and call progress tones as well as the signalling and supervision information.