The S5T8554B03 consists of on-chip PCM encoders, decoders (PCM CODECs) and PCM line filter. This device provides all the functions required to interface a full-duplex voice telephone circuit, digital answering phone. This device is designed to perform the transmit encoding and receive decoding as well as the transmit and receive filtering function in PCM system. Also it is intended to be used at the analog termination of a PCM line / trunk. This device provide the Band pass filtering of the analog signals prior to encoding and after decoding. This combination device performs the encoding and decoding of voice and call progress tones as well as the signaling and supervision information.