Technical data

SYSTEM CONNECTOR INTERFACE

LZT 123 8020 R1A

5.7 Analogue Audio

Pin Signal Dir Description

57 AFMS O Audio from mobile station

59 ATMS I Audio to mobile station

60 AGND - Ground (return) for analogue audio

ATMS is the audio input, and AFMS is the audio output, of the

radio device. These signals can be used in car kit mode.

There are three factory-set audio profiles:

• portable handsfree

• handset

• car kit

Portable handsfree is the factory-set default profile. The

modification, configuration, manipulation and storage of audio

profiles is achieved with the AT*E2EAMS (Audio Profile

Modification) and AT*E2APR (Audio Profile).

5.7.1 Audio To Mobile Station - ATMS

ATMS is the analogue audio input to the radio device.

Internally, the signal is sent to the CODEC (COder/DECoder),

where it is converted to digital audio in PCM (Pulse Code

Modulation) format. The encoded audio is sent to PCMOUT via

the internal PCM bus.

ATMS provides a DC bias when it is used as the microphone

input in Portable Handsfree applications. All other sources must

be a.c.coupled to avoid attenuation of low frequencies, and to

prevent incorrect biasing or damage to the ATMS input. Use a

capacitor greater than the value shown in the table below.

The ATMS input is a passive network followed by the transmit

part of the CODEC.

Parameter Limit

Application driving impedance (0.3 - 3.5 kHz)

≤ 300 Ω

AC coupling capacitance

≥ 1 µF

Radio device input impedance (0.3 - 3.5 kHz) > 50 kΩ

Low frequency cut-off (- 3 dB) 300 Hz ± 50 Hz

High frequency cut-off (– 3 dB) > 3500 Hz ± 50 Hz

Output d.c. bias level car kit mode 0 V