SI2457-D-FT Silicon Laboratories Inc, SI2457-D-FT Datasheet - Page 220

• Manufacturer Part Number: SI2457-D-FT
• Description: IC ISOMODEM SYSTEM-SIDE 24TSSOP
• Manufacturer: Silicon Laboratories Inc

Specifications of SI2457-D-FT

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

AN93
7.7.5. Simplex Speakerphone Configuration
Configuring the modem to automatically switch between local talker and remote talker is as follows:
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For manual operation (push-to-talk):
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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).
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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).
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 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.
Host to Modem Commands / Data
AT:U199&FFF5
AT:U72,0900
AT+VSP=1
Table 136. Speakerphone Configuration (Continued)
Modem to Host
Result Codes/
Rev. 1.3
Data
OK
OK
OK
Configure Si3000 Register 9:
0 dB Line Out attenuation
0 dB Speaker output attenuation
Enable speakerphone voice path. See Figure 29
on page 188 for details.
Enable the microphone and speaker paths
to the codec.
Local Modem Actions