7.3 Feature Description

7.3.1 Tone Mode Start-up Timing

VMIC

VTONE

VSHUNT

VMICPWR

VREM

2.35V

0V

0V

2.5V

0V

2.5V

0V

2.5V

0V

2.5V

2.5V

tOFFB

tREG.

tM2T.

tCAL.

tACK.

tONA.

Figure 7-2. Tone Mode Start-up Timing

The tone mode start-up sequence is as follows:

1. After detecting VMIC > 2.35V, the switch connecting the MIC and REM pins together (Switch B) is opened

after time tOFFB.

2. After a delay of tONA after VMIC > 2.35V, the VSHUNT and MICPWR pins are shorted (with Switch A). The

microphone is enabled by turning on the FET switch that is controlled by the MICPWR pin.

3. After a delay to allow the switches to settle, tM2T after VMIC > 2.35V, the CD326x sends a preset

acknowledge (ACK) tone sequence.

4. The specially enabled audio interface detects the ACK sequence and authenticates the presence of the

CD326x.

7.3.2 Authentication

To validate connectivity with a specially enabled audio interface, the CD326x provides an authentication

sequence upon start-up. After enabling tone mode (applying VMIC > 2.35V typical), the specially enabled audio

interface waits to receive an acknowledgment from the CD326x. This acknowledgment is a tone sequence

similar to a button press when operating as tone mode. When the CD326x recognizes tone mode upon power-

up, the CD326x sends an acknowledgment (ACK) tone sequence to the specially enabled audio interface. The

tone frequency is identical to the S1 button press tone for the CD3268 and to the S2 button press tone for the

CD3269. However, the ACK tone sequence generates the second tone to be 3.7ms longer compared to the

standard tone sequence for button presses.

The specially enabled audio interface reads the tone sequence as shown in Figure 7-6. The specially enabled

audio interface takes three samples: the first to determine calibration frequency, the second to determine the

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