The MT8880C/C-1 is a monolithic DTMF transceiver with call progress filter. It is fabricated in Mitel’s ISO2-CMOS technology, which provides low power dissipation and high reliability. The DTMF receiver is based upon the industry standard MT8870 monolithic DTMF receiver; the transmitter utilizes a switched capacitor D/A converter for low distortion, high accuracy DTMF signalling. Internal counters provide a burst mode such that tone bursts can be transmitted with precise timing. A call progress filter can be selected allowing a microprocessor to analyze call progress tones. A standard microprocessor bus is provided and is directly compatible with 6800 series microprocessors. The MT8880C-1 is functionally identical to the MT8880C except for the performance of the receiver section, which is enhanced to accept and reject lower signal levels.