User Manual
Table Of Contents
- Document History
- Introduction
- Product Concept
- GSM Application Interface
- GSM/GPRS Operating Modes
- Power Supply
- Power Up / Down Scenarios
- Automatic GPRS Multislot Class Change
- Charging Control of the GSM Part
- Power Saving
- Summary of State Transitions (Except SLEEP Mode)
- RTC Backup for GSM Part of XT55/56
- Serial Interfaces of the XT55/56 GSM Part
- Audio Interfaces
- SIM Interface
- Control Signals
- GPS Application Interface
- GSM and GPS Antenna Interfaces
- Electrical, Reliability and Radio Characteristics
- Mechanics
- Reference Approval
- Example Applications
- List of Parts and Accessories
XT55/56 Hardware Interface Description
Confidential / Preliminary
s
XT55/56_hd_v02.96 Page 59 of 125 18.08.2005
3.10 Audio Interfaces
XT55/56 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
)
GSM_MICP1
GSM_MICN1
GSM_MICP2
GSM_MICN2
GSM_EPP1
GSM_EPN1
GSM_EPP2
GSM_EPN2
GSM_SCLK
GSM_RXDDA
I
GSM_TFSDAI
GSM_RFSDAI
GSM_TXDDAI
Figure 16: Audio block diagram
XT55/56 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
31 on page 105 summarizes the characteristics of the various audio modes and shows what
parameters are supported in each mode.