The 821024 is a single-chip, four channel PCM CODEC with on-chip filters. The device provides analog-to-digital and digital-to-analog conversions and supports both a-law and m-law companding. The digital filters in 821024 provides the necessary transmit and receive filtering for voice telephone circuit to interface with time-division multiplexed systems. All of the digital filters are performed in digital signal processors operating from an internal clock, which is derived from MCLK. The fixed filters set the transmit and receive gain and frequency response.