Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 187)

AN93
Rev. 1.3 187
7.2. Voice Reference—Overview
This document uses the term “handset mode” to describe the use of the microphone (MIC) and speaker (SPKRL/
SPKRR) connections on the Si3000. The term “hands-free or speakerphone mode” describes the use of the line
input (LINEI) and line out (LINEO) connections on the Si3000.
The term “handset” describes a handheld device containing a microphone and a speaker with a four-wire
connection for microphone signal pair (MIC/MBIAS and GND) and speaker signal pair (SPKRL and GND or
SPKRL and SPKRR). The Si3000 datasheet uses the term “handset” to describe a two-wire device that is
connected directly to the Public Switch Telephone Network (PSTN). This two-wire device is referenced as a
“telephone instrument” to avoid confusion.
The Si24xx-VMB EVB Rev. 2.0 mainboard with Si24xx2G-QFN Rev 1.0 daughtercard serves as the general
evaluation platform for the Si2494/39 parts. See the Si24xx-VMB Global Voice ISOmodem EVB User’s Guide for
details.
Figure 29 illustrates the handset and speakerphone voice path. The gain registers in Figure 29 use a 4.12 format,
with a range of 0x0001 (–72.247 dB) to 0xFFFF (24.082 dB). For the Si3000-to-DAA gain (UB1) and the DAA-to-
Si3000 gain (UB5), a value of zero is used to disable the path.
The Si2494/39 enters voice mode with +FCLASS=8. Figure 30 illustrates the gain and signal selection options for
the Si3000 codec. Table 117 provides a summary of how the +VLS command is used to control the various voice
mode operations. Table 118 shows the summary of +FCLASS and IDLE state transitions and the expected
responses.