Silicon Laboratories SI2494/39, SI2493/57/34/15/04 manual Voice Reference-Overview

AN93

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.

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