Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 173)

AN93
Rev. 1.3 173
7. Handset, TAM, and Speakerphone Operation
This section covers the voice functionality of the Si2494/39. The voice features of the Si2494/39 are divided into
three major categories: handset, telephone answering machine (TAM), and speakerphone. The Si2494/39
implements ITU-T V.253 commands for TAM and speakerphone operation. The TAM voice compression support
includes the following formats:
 Signed linear 8-bit, 64 kbps
 Unsigned linear 8-bit, 64 kbps
 G.711 µ-law 8-bit, 64 kbps
 G.711 A-law 8-bit, 64 kbps
 G.726 ADPCM 2-bit, 16 kbps
 G.726 ADPCM 4-bit, 32 kbps
All formats use a fixed 8 kHz sampling rate. For most applications, the user wants a high-quality message format
(64 kbps) for the Outgoing Message (OGM) and is less concerned about the quality of the Incoming Message
(ICM).
Speakerphone operation employs an acoustical echo canceller (AEC), acoustical echo suppressor (AES), double-
talk detector (DTD), and line-echo canceller (LEC). This solution provides the following performance:
 Programmable echo tail filter length: up to 64 ms
 Convergence speed (white noise): less than 1.6 s
 Single-talk echo suppression: better than 48 dB
 Double-talk echo suppression: better than 30 dB
The software reference section presents the implemented V.253 AT Commands, V.253 <DLE> commands, V.253
<DLE> events, and U registers. The voice reference section covers the functional operation of handset, TAM, and
speakerphone modes and includes use cases with programming examples.
7.1. Software Reference
7.1.1. AT Command Set
In Voice Command State, AT commands are used to control the DCE. The DCE responds with verbose response
strings during Voice Command State. During the Voice Transmit, Voice Receive, and Voice Duplex States, the
<DLE> shielded commands are used. The <DLE> events can appear in all states.
7.1.2. AT+ Extended Commands
Table 110. Extended AT+ Command Set
Command Action
+FCLASS = <mode>
Data/Voice Mode Selection
<mode>
Description
0 Data (default)
8 Voice mode
256 SMS mode
Note: An ATH command will automatically transition the DCE to +FCLASS=0.
+IPR = <rate>
Fixed DTE Rate
<rate>
Description
0 Automatically detect the baud rate.
[BPS] The decimal value of the rate in bits per second.
The <rate> parameter represents the DTE rate in bps and may be set to any of the fol-
lowing values: 300, 600, 1200, 2400, 4800, 7200, 9600, 12000, 14400, 19200, 38400,
57600, 115200, 230400, 245760, and 307200.