Gemalto M2M GmbH MC56 User Manual

MC55/56 Hardware Interface Description
Confidential / Preliminary

MC55/56_hd_v03.00

Page 54 of 104

16.08.2005

3.10 Audio

interfaces

MC55/56 comprises three audio interfaces available on the board-to-board connector:
• Two analog audio interfaces, each with a balanced analog microphone input and a

balanced analog earpiece output. The second analog interface provides a supply circuit
to feed an active microphone.

• Serial digital audio interface (DAI) using PCM (Pulse Code Modulation) to encode analog

voice signals into digital bit streams.

This means you can connect up to three audio devices in any combination, although analog
and digital audio cannot be operated at the same time. Using the AT^SAIC command you
can easily switch back and forth.

M
U
X

ADC

DSP

DAC

Air
Interface

Digital
Audio
Interface
(DAI)

MICP1

MICN1

MICP2

MICN2

EPP1

EPN1

EPP2

EPN2

SCLK

RXDDAI

TFSDAI

RFSDAI

TXDDAI

Figure 16: Audio block diagram

MC55/56 offers six audio modes which can be selected with the AT^SNFS command, no
matter which of the three interfaces is currently active. The electrical characteristics of the
voiceband part vary with the audio mode. For example, sending and receiving amplification,
sidetone paths, noise suppression etc. depend on the selected mode and can be altered with
AT commands (except for mode 1).

On each audio interface you can use all audio AT commands specified in [1] to alter
parameters. The only exception are the DAC and ADC gain amplifier attenuation
<outBbcGain> and <inBbcGain> which cannot be modified when the digital audio interface is
used, since in this case the DAC and ADC are switched off.

Please refer to Chapter 3.10 for specifications of the audio interface and an overview of the
audio parameters. Detailed instructions on using AT commands are presented in [1]. Table
29 on page 87 summarizes the characteristics of the various audio modes and shows what
parameters are supported in each mode.