User guide

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Description and non-contractual illustrations in this document are given as an indication only.
ERCO & GENER reserves the right to make any modifications.
7.4 Audio
The audio interface is a standard interface for connecting a telephone handset (the command AT$VSELECT
enables you to select the handset, please refer to ERCO & GENER "Commands List").
Echo cancellation (see command AT$MICAEC) and noise reduction features are also available to improve
the audio quality in hands-free applications.
ERCO & GENER recommend the use of the following cable: DATA/AUDIO Sub D 9pts Fem / Sub HD 15pts
Male / RJ9 (order code 4404000205) and a telephone handset (order code 3153400000).
Table: Pin identification
Pin name SUBD 9 F pin number SUBD 15 M-HD pin number
DCD/Buzzer 1 1
RXD 2 6
TXD 3 2
DTR 4 8
GND 5 9
DSR 6 7
RTS 7 12
CTS 8 11
RI/3.8V 9 13
RJ9 pin number
Micro + 1 4
Speaker + 2 10
Speaker - 3 15
Micro - 4 5
7.4.1 Microphone
Differential microphone inputs are used to help reduce common–mode and TDMA noise. They are ESD
protected.
An electret type microphone (0.5 mA / 2 Volts) may be connected directly to these inputs allowing the
connexion of a telephone handset.
The microphone impedance is approximately 36 k.
The gain of the microphone input may be internally adjusted by a differential amplifier and may be defined by
using the command AT+PREAMP (see the ERCO & GENER “Commands List”).
The amplifier has a gain of 25.6 dB and a Bias generator providing an external voltage of 2 or 2.5V for the
Bias microphone.
Table: Pins description
Signal name
Pin number Sub HD
Connector
I/O Type Description
CMIC2P 4 I Analogue Microphone +ve
CMIC2N 5 I Analogue Microphone -ve