MC45 Hardware Interface Description
P R E L I M I N A R Y
MC45_HD_01_V00.02a
Page 49 of 90
12.08.2002
3.6 Audio interfaces
MC45 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, all 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
MC45 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 6.5 for specifications of the audio interface and an overview of the
audio parameters. Detailed instructions on using AT commands are presented in the "MC45
AT Command Set" [1]. Table 31
on page 83 summarizes the characteristics of the various
audio modes and shows what parameters are supported in each mode.
