Audio transmitter, button (no mic, 3µA) and tone mode (mic, 110µA), 165kHz ACK frequency

The CD326x supports two operating modes; button mode and tone mode. Button mode offers no microphone support. Button mode passes the DC voltage from an external switch-resistor network (tied to the REM pin) to the MIC pin to measure the voltage externally. Tone mode offers microphone support and senses button presses based on an external switch-resistor network (tied to the REM pin). Tone mode generates corresponding ultrasonic signals that are superimposed (via a driver output on the TONE pin) on the system MICBIAS line. These signals control audio functions when connected to a specially enabled audio interface. The input DC bias level provided on the MIC pin controls button or tone mode selection. During tone mode, the CD326x also provides functionality to control or bias an external MEMS (micro-electrical-mechanical systems) technology microphone module.