7 Detailed Description

7.1 Overview

The CD326x communicates with a specially enabled audio interface to report detected remote button presses.

Two basic modes are supported—button mode and tone mode—and the active mode is determined by the DC

bias voltage level on the MIC pin (2.5V and 2.0V for tone mode and button mode respectively). The bias voltage

is typically provided by a specially enabled audio interface.

During button mode operation, the CD326x operates as a pass-through element that connects the DC voltage on

the REM pin to the MIC pin. The REM pin is connected to an external switch-resistor network where each switch

represents a unique button. When a button is pressed, the DC level on the bias line is changed before being

externally detected and measured by a specially enabled audio interface. Button mode does not support bias or

control of an external microphone. In Figure 7-1, button mode is represented by switch A being open and switch

B being closed.

During tone mode operation, the CD326x supports the use of an external MEMS microphone module. The

module can be biased from the MICPWR pin or the MICPWR pin can be used to control an external circuit

to enable or disable power to the microphone as shown in Figure 8-1. The REM pin is used to detect

button presses from an external switch-resistor network, and the CD326x then generates a corresponding,

ultrasonic signal on the TONE pin. The tones are unique to each button and are externally coupled to the

system microphone bias line and MIC pin as seen in Figure 8-1. A specially enabled audio interface is able to

determine the frequency of the tone, decode the tone into a specific button press, and control system operations

accordingly. Most commonly, three button switches are used in the external switch-resistor network tied to

the REM pin with the following functions: volume up, volume down, and center button. However, the CD326x

supports up to four unique buttons, allowing for more customized functionality.

The CD326x also provides authentication, shunt regulation, and power-on-reset (POR) functionality. These are

described in Section 7.3.

7.2 Functional Block Diagram

VSHUNT

MIC

TONE

GND

MICPWR

REM

1.56V

S

Q

Q

R

Power-on

reset

+

Switch A

Switch B

Impedence

detector

Tone

generator

+

2.3V

Figure 7-1. Functional Block Diagram

CD3268A, CD3269A

SCHS463 – MAY 2025

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