Silicon Laboratories SI2493/57/34/15/04, SI2494/39 manual Simplex Speakerphone Configuration

AN93

Table 136. Speakerphone Configuration (Continued)

Host to Modem Commands / Data	Modem to Host	Local Modem Actions
	Result Codes/
	Data
		Configure Si3000 Register 9:
AT:U72,0900	OK	0 dB Line Out attenuation
		0 dB Speaker output attenuation
AT+VSP=1	OK	Enable speakerphone voice path. See Figure 29
		on page 188 for details.
AT:U199&FFF5	OK	Enable the microphone and speaker paths
		to the codec.

7.7.5. Simplex Speakerphone Configuration

Configuring the modem to automatically switch between local talker and remote talker is as follows:

For the SSP auto-switch (VOX) function, set SSP_FLAG to 1 (U199 [6] = 1) and SSP_PTT to 0 (U199 [7] = 0).

Set the speaker and microphone level thresholds, which determine whether remote speech or local speech is active. The thresholds are defined in U19C and U19D. Typical values for the speaker and microphone thresholds are 0x700 and 0x600, respectively. These thresholds are not affected by the speaker and microphone control gains UB5 and UB1.

Set the holding time, which is the time that the SSP holds the current mode after the signal level falls below the threshold. Holding time prevents frequent mode switching between RX and TX. A typical value for holding time is 0xC8 (200 ms).

For manual operation (push-to-talk):

Set SSP_FLAG to 1 (U199 [6] = 1) and SSP_PTT to 1 (U199 [7] = 1).

Use the SSP_LOCTALK bit (U199 [8]) to set the speech direction: U199 [8] = 1 for local talker; U199 [8] = 0 for remote talker.

U1D8 is the break-through threshold for the speaker signal in SSP auto-switch mode. If the speaker signal is above the threshold U1D8 and holds at least for the holding time, the direction is switched to remote talker, no matter how strong the signal in the microphone is. To disable break-through, set the threshold to 7FFFh (AT:U1D8,7FFF).

U1D8 greater than U1D6: when the speaker signal is greater than or equal to U1D8, the microphone is muted and speaker unmuted immediately, regardless of the microphone holding time. When the speaker signal is greater than U1D6 but less than U1D8, the speaker signal goes through after the expiration of the microphone holding time.

U1D8 less than U1D6: the break-through threshold U1D8 takes over and the speaker level threshold U1D6 becomes inactive.

The default value for U1D8 is 7FFFh. A typical value for U1D8 is 0x1000. Adjust U1D8 according to the needs of the application.

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