RFX144V24-S23 and RFX96V24-S23 Modem Designer’s Guide
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1070
No. 68
Room Monitor Volume Control
The amplitude of the IIA DAC signal in the Room Monitor Mode can be adjusted. An increase in the value written to the
modem shifts the value sent to the IIA DAC left by one, thereby doubling its amplitude.
Format:
16 bits, unsigned
Equation:
dB gain = 6 * x
Range:
0 < x < 7FFFh
Default Value:
0
No. 69
Speaker Volume Control (SPKR Output Pin)
The SPKR output monitors the output of the receive continuous anti-aliasing filter. Bits 4 and 5 of this word establish the
attenuation applied to the SPKR output as follows:
Format:
16 bits, unsigned
Encoding:
Bit 5
Bit 4
Description
0
0
Squelch
0
1
0 dB loss
1
0
6 dB loss
1
1
12 dB loss
During squelch, the SPKR output is clamped to voltage VC.
The SPKR output can drive a load as low as 300 ohms, but is not intended to drive an 8 ohm or 50 ohm speaker coil directly.
It is recommended that the SPKR output be connected to an external audio power amplifier input.
No. 70
Speakerphone Transmit Speech Active
The speakerphone transmit speech active bit indicates transmit (microphone) speech activity. The bit is set or reset by the
transmit speech detector which distinguishes the actual room talker from room noise and the echo from the loudspeaker.
Format:
Single bit (bit 7 of register 0)
Threshold:
Depends on room noise floor and loudspeaker echo level, which are adjusted automatically by the
speakerphone algorithm.
Default Value:
0 (Off)
No. 71
Speakerphone Receive Speech Active
The speakerphone receive speech active bit indicates receive (line) speech activity. The bit is set or reset by the receive
speech detector which distinguishes the actual remote talker from line noise and the hybrid echo.
Format:
Single bit (bit 6 of register 0)
Threshold:
Depends on line noise floor and hybrid echo level, which are adjusted automatically by the
speakerphone algorithm.
Default Value:
0 (Off)
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