WM8904ECSSLASHR datasheet(183/188 Pages) WOLFSON

183 / 188 page

Pre-Production

WM8904

PP, Rev 3.3, September 2012

183

MIC DETECTION SEQUENCE USING MICBIAS CURRENT

This section details an example sequence which summarises how the host processor can configure

and detect the events supported by the MICBIAS current detect function (see “Electret Condenser

Microphone Interface”):



Mic insertion/removal



Hook switch press/release

Figure 72 shows an example of how the MICBIAS current flow varies versus time, during mic

insertion and hook switch events. The Y axis is annotated with the Mic detection thresholds, and the

X axis is annotated with the stages of an example sequence as detailed in Table 96, to illustrate how

the host processor can implement mic insertion and hook switch detection.

The sequence assumes that the microphone insertion and hook switch detection functions are

monitored by polling the interrupt flags using the control interface. Note that the maximum mechanical

bounce times for mic insertion and removal must be fully understood by the software programmer.

A GPIO pin could be used as an alternative mechanism to monitor the MICBIAS detection functions.

This enables the host processor to detect mechanical bounce at any time.

Time

Mic Hook Switch

Threshold

Mic Detect Interrupt

(1) (2)

(4)

(5)

(6)

(7)

(8)

(9)

TDET

Mic Detect

Threshold

Hysteresis

(3)

(10)

TSHORT

Mic Detect Interrupt Polarity

Mic Short Interrupt

Mic Short Interrupt Polarity

MIC_DET_EINT

MIC_DET_EINT_POL

MIC_SHRT_EINT

MIC_SHRT_EINT_POL

HOST

PROCESSOR

Read the Mic detect interrupt

flag. If high, can then set

MIC_DET_EINT_POL to 1,

but only if mechanical bounce

phase has finished. Clear

MIC_DET_EINT by writing ‘1’.

Read the Hook switch interrupt flag.

If high, can immediately set

MIC_SHRT_EINT_POL to 1. Clear

MIC_SHRT_EINT by writing ‘1’.

Read the Hook switch interrupt flag. If high, can

immediately clear MIC_SHRT_EINT_POL to 0.

Clear MIC_SHRT_EINT by writing ‘1’.

Read the Mic detect interrupt flag. If high, can

then clear MIC_DET_EINT_POL to 0, but only

if mechanical bounce phase has finished.

Clear MIC_DET_EINT by writing ‘1’.

Step

(1) (2)

(4)

(5)

(6)

(7)

(8)

(9)

(3)

(10)

Step

Example plot of MICBIAS Current versus time

Mic inserted

Hook switch

pressed

Figure 72 Mic Insert and Hook Switch Detect: Example MICBIAS Current Plot

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