wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 172

• Manufacturer Part Number: wm8918
• Description: Ultra Low Power Dac For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

WM8918
MIC DETECTION SEQUENCE USING MICBIAS CURRENT
Figure 72 Mic Insert and Hook Switch Detect: Example MICBIAS Current Plot
w
Example plot of MICBIAS Current versus time
Step
Mic Detect Interrupt
Mic Detect Interrupt Polarity
Mic Short Interrupt
Mic Short Interrupt Polarity
Step
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’.
(1)
(1)
(2)
(2)
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”):
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 89, 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.
T
(3)
DET
(3)
•
•
Mic insertion/removal
Hook switch press/release
(4)
(4)
(5)
(5)
Read the Hook switch interrupt flag.
If high, can immediately set
MIC_SHRT_EINT_POL to 1. Clear
MIC_SHRT_EINT by writing ‘1’.
Mic inserted
T
SHORT
Hook switch
pressed
(6)
(6)
Read the Hook switch interrupt flag. If high, can
immediately clear MIC_SHRT_EINT_POL to 0.
Clear MIC_SHRT_EINT by writing ‘1’.
(7)
(7)
T
SHORT
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’.
(8)
(8)
(9)
(9)
T
(10)
(10)
DET
PD, Rev 4.0, September 2010
Hysteresis
MIC_SHRT_EINT_POL
MIC_DET_EINT_POL
Mic Detect
Mic Hook Switch
Threshold
Threshold
MIC_SHRT_EINT
MIC_DET_EINT
Production Data
Time
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