The PD63335 is a stereo sound codec LSI that enables full-duplex communications and features two channels each of on-chip 16-bit ADC and DAC circuits for mutual conversion between digital signals and audio analog signals (having a maximum signal bandwidth of 20 kHz). The analog signal input block enables four pairs of stereo signals plus three monaural signals to be output from the output stage's internal mixing circuit, which can then be multiplexed and input to the ADC. One type of monaural signal can be selected from two external pins via a selector as a monaural signal connected to an internal microphone amplifier (MIC amp), with selectable gain of 0 dB or 20 dB. The analog signal output block enables mixed output of analog signals output by the DAC, four pairs of stereo analog signals, and an output signal from the MIC amp, and the volume of each signal can be controlled independently before mixing. The digital audio signal I/O block supports an audio-type serial interface (two's complement). In addition, a clocked serial interface (CSI) can be used for direct connection to a general-purpose microcontroller for access to internal registers such as for volume control.