wm8903 Wolfson Microelectronics plc, wm8903 Datasheet - Page 156

• Manufacturer Part Number: wm8903
• Description: Ultra Low Power Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

WM8903
Table 78 Mic Insert and Hook Switch Detect: Example Sequence
w
1
2
3
4
5
6
7
8
9
10
STEP
Mic not inserted. To detect mic insertion, Host processor must initialise interrupts and clear MICDET_INV = 0. At every
step, the host processor should poll the interrupt status register.
Mechanical bounce of jack socket during Mic insertion. Host processor may already detect a mic insertion interrupt
during this step. Once detected, the host processor can set MICDET_INV = 1, unless mechanical bounce can last
longer than the shortest possible T
Mic fully inserted. If not already cleared, Host processor must now set MICDET_INV = 1. To detect Hook switch press,
Host processor must clear MICSHRT_INV = 0. At this step, the diagram shows no AC current swing, due to a very low
ambient noise level.
Mic fully inserted. Diagram shows AC current swing due to high levels of background noise (such as wind).
Mechanical bounce during hook switch press. The hook switch interrupt is unlikely to be set during this step, because 10
successive samples of the MICBIAS current exceeding the hook switch threshold have not yet been sampled.
Hook switch is fully pressed down. After T
switch threshold have been detected, hence a hook switch interrupt will be generated, and the host processor can
immediately set MICSHRT_INV = 1.
Mechanical bounce during hook switch release. The hook switch interrupt is unlikely to be set during this step, because
10 successive samples of the MICBIAS current lower than the hook switch threshold have not yet been sampled.
Hook switch fully released. After T
threshold have been detected, hence a hook switch interrupt will be generated, and the host processor can immediately
clear MICSHRT_INV = 0.
Mechanical bounce of jack socket during Mic removal. Host processor may already detect a mic removal interrupt during
this step. Once detected, the host processor can clear MICDET_INV = 0, unless mechanical bounce can last longer
than the shortest possible T
Mic fully removed. If not already set, Host processor must now clear MICDET_INV = 0.
Alternatively, utilising a GPIO pin to monitor the MICBIAS current detect functionality permits the
host processor to monitor the steady state of microphone detection or hook switch press functions.
Because the GPIO shows the steady state condition, software de-bounce may be easier to
implement in the host processor, dependant on the processor performance characteristics, hence
use of the GPIO is likely to simplify the rejection of mechanical bounce. Changes of state in the
GPIO pin are also subject to the time delays t
Further details can be found in the applications note WAN_0213 “WM8903 ECM mic detection using
MICBIAS current”.
DET
, in which case the host processor should not clear MICDET_INV = 0 until step 10.
SHORT
DET
, in which case the host processor should not set MICDET_INV = 1 until step 3.
, 10 successive samples of the MICBIAS current lower than the hook switch
SHORT
, 10 successive samples of the MICBIAS current exceeding the hook
DETAILS
DET
and t
SHORT
.
PP, Rev 3.1, August 2009
Pre-Production
156