Analog Audio Accessory Detection - Nokia NSE–3 SERIES Service Manual

PAMS
Technical Documentation

Analog Audio Accessory Detection

In XEAR signal there is a 47 kW pullup in the transceiver and 6.8 kW
pull–down to SGND in accessory. The XEAR is pulled down when an
accessory is connected, and pulled up when disconnected. The XEAR is
connected to the HookDet line (in MAD), an interrupt is given due to both
connection and disconnection. There is filtering between XEAR and
HookDet to prevent audio signal giving unwanted interrupts.
External accessory notices powered–up phone by detecting voltage in
XMIC line. In Table 23 there is a truth table for detection signals.
Accessory connected
No accessory connected
Headset HDC–9 with a button switch
pressed
Headset HDC–9 with a button switch re-
leased
Handsfree (HFU–1)
Headset Detection
The external headset device is connected to the system connector, from
which the signals are routed to COBBA headset microphone inputs and
earphone outputs. In the XMIC line there is a (47 + 2.2) kW pullup in the
transceiver. The microphone is a low resistance pulldown compared to
the transceiver pullup.
When there is no call going, the AUXOUT is in high impedance state and
the XMIC is pulled up. When a headset is connected, the XMIC is pulled
down. The XMIC is connected to the HeadDet line (in MAD), an interrupt
is given due to both connection and disconnection. There is filtering be-
tween the XMIC and the HeadDet to prevent audio signal giving un-
wanted interrupts (when an accessory is connected).
In the XEAR line there is a 47 kW pullup in the transceiver. The earphone
is a low resistance pulldown compared to the transceiver pullup. When a
remote control switch is open, there is a capacitor in series with the ear-
phone, so the XEAR (and HookDet) is pulled up by the phone. When the
switch is closed, the XEAR (and HookDet) is pulled down via the ear-
phone. So both press and release of the button gives an interrupt.
During a call there is a bias voltage (1.5 V) in the AUXOUT, and the
HeadDet cannot be used. The headset interrupts should to be disabled
during a call and the EAD line (AD converter in CCONT) should be polled
to see if the headset is disconnected.
Original 11/97
HookDet HeadDet
High High
Low Low
High Low *)
Low High
NSE–3
System Module
Notes
Pullups in the transceiver
XEAR and XMIC loaded (dc)
XEAR unloaded (dc)
XEAR loaded (dc)
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