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.