The Motorola MC33218A Voice Switched Speakerphone Circuit incorporates the necessary amplifiers, attenuators, level detectors, and control algorithm to form the heart of a high quality handsfree speakerphone system. Included are a microphone amplifier with mute, transmit and receive attenuators, a background monitoring system for both the transmit and receive paths, and level detectors for each path. An AGC system reduces the receive gain on long lines where loop current and power are in short supply. A dial tone detector prevents fading of dial tone. A Chip Disable pin permits conserving power when the circuit is not in use. Additionally, the MC33218A has a serial data port which permits microprocessor control of the receive volume level, microphone mute, attenuator range, and selection of transmit, receive, idle or normal modes. The data port can be operated at up to 1.0 MHz. The MC33218A can be operated from a power supply, or from the telephone line, requiring typically 4.6 mA. It can be used in conjunction with a variety of speech networks. Applications include not only speakerphones, but intercoms and other voice switched devices. Supply Voltage Range: 2.7 to 6.5 V