Headset Connections - Nokia NPL-4 Series Manual

NPL-4/5/RM-104
System Module and User Interface

Headset connections

NPL-4/5 is designed to support fully differential external audio accessory connection. A
headset can be directly connected to Tomahawk system connector. Mono and stereo
audios are supported to earpieces and mono for microphone audios.
Headset implementation uses separate microphone and earpiece signals. The accessory is
detected by the HeadInt signal when the plug is inserted. Normally when no plug is
present the internal pull-down on the HF pin pulls down the HeadInt signal. Due to that
the comparator level is 1.9V the HeadInt signal will not change state even if the HF out-
put is biased to 0.8V. When the plug is inserted the switch is opened and the HeadInt
signal is pulled up by the internal pull-up. The 1.9V threshold level is reached and the
comparator output changes to low state causing an interrupt.
The hook signal is generated by creating a short circuit between the headset microphone
signals. When no accessory is present, the UEMEK internal resistor pulls up the HookInt
signal. When the accessory is inserted and the microphone path is biased the HookInt
signal decreases to 1.8V due to the microphone bias current flowing through the resistor.
When the button is pressed the microphone signals are connected together, and the
HookInt input will get half of micbias dc value 1.1 V. This change in DC level will cause
the HookInt comparator output to change state, in this case from 0 to 1. The button can
be used for answering incoming calls but not to initiate outgoing calls.
Copyright © 2005 Nokia Corporation. All rights reserved.
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