Voice Receive Mode
Voice Receive Mode is entered when the DTE issues the #VRX command because
it wants to receive voice data. This typically occurs when either recording
a greeting message, or when recording voice messages from a remote station.
In Voice Receive Mode, voice samples from the modem analog-to-digital converter
(ADC) are sent to the ADPCM codec for compression, and can then be read
by the host. AT commands control the codec bits-per-sample rate and select
(optional) silence deletion including adjustment of the silence detection
period.
In this mode, the modem detects and reports DTMF, dial tone, busy tone cadence,
and inactivity (periods of silence) as enabled by the #VTD and #VSS commands,
respectively. The modem can exit the Voice Receive Mode only via a DTE Key
Abort, or via Deadman Timer expiration (S30).
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