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536EX Chipset Developer’s Manual 79
Intel Confidential
IS-101 Voice Mode AT Commands
+VRX none
Record Mode: This command causes the modem to enter record mode to record voice messages.
Upon receiving the AT+VRX command, the modem responds to the DTE with a ‘CONNECT’ message
at the current DTE-to-modem rate. It is important that the UART DTE-to-modem rate be equal or
higher to the compression-scheme-required UART data rate (for example, CL1 at 4800 samples/
second requires 57,600 bps). If the DTE-to-modem data rate is lower than the compression-scheme-
required UART data rate, then data may be lost or may be garbled during playback of the message.
After sending the ‘CONNECT’ message, the modem then sends digitized voice data that is <DLE>-
shielded to the DTE. The modem buffers the data to ensure steady voice delivery even though the
voice data may be transferred to the DTE in bursts. The DTE may use the <DLE><NUL> shielded code
as a no-operation command to refresh the inactivity timer.
During voice receive mode, the modem informs the DTE about pertinent events that may prompt the
DTE to terminate the voice receive state. The DCE sends <DLE> codes for detection of signals such as
busy tone, dial tone, DTMF tone, and codes for ‘Presumed End of Message’ or ‘Presumed Hang-up.’
Record mode is terminated whenever the modem issues a <DLE><ESC> command or provides a DTE/
DCE inactivity timer time-out. Upon detecting the terminating character, the modem stops sampling the
analog data. The modem then terminates record mode by sending the remaining voice data stored in
its internal buffer, <DLE><ETX>, and an ‘OK’ message to the DTE.
In some situations, the application software may want to abort record mode and immediately perform a
new function without first reading all the recorded voice data from the modem’s internal buffer (for
example, after detecting fax calling tone). This is accomplished by sending <DLE><!> to the modem
while in record mode. Upon seeing <DLE><!>, the modem terminates record mode, clears the
modem’s internal record buffer, and issues a <DLE><ETX> to the DTE followed by an ‘OK’ message.
The modem may immediately abort record mode if it receives either an AT+VIT=m time-out or a DTR
toggle. If +VIT≠0 and the modem has not received any data or a <DLE><NUL> code before the +VIT
timer times out, then the modem immediately aborts record mode. The modem then hangs up the line
and changes to data mode (+FCLASS=0). If the UART DTR signal is toggled on-off-on, then the
modem follows the &Dn setting. If configured for &D2 or &D3, the modem immediately aborts record
mode, hangs up the line, and changes to data mode (+FCLASS=0).
NOTE: The voice sampling rate and sampling mode must be the same values as used during record
mode.
+VSD=m see ‘m’
Silence Detection (Quiet and Silence): This command allows the DTE to set two parameters: <sds>
reports the sensitivity for silence detection, and <sdi> reports the length of silence required for the
DCE to report silence when receiving voice.
The <DLE><s> silence timer starts immediately after entering record mode. The modem stops using
the <DLE><s> timer and starts using the <DLE><q> timer if:
• the <DLE><s> silence timer has timed out and a <DLE><s> code has been sent to the DTE, or
• if noise or voice energy has been detected above the silence detection threshold (as defined by
<sds>).
m = <sds>, <sdi>
Defaults: m = 128, 50
<sds> Silence Sensitivity: If the received analog signal stays below this specified level for a user-
specified time delay, the modem sends <DLE><q> to the DTE. The modem sends only one <DLE><q>
to the DTE each time record mode +VRX is entered.
Range: 121–131
128* Nominal level
<sdi> Length of Silence: This parameter sets the period of silence that must elapse before the DCE
reports silence (as detected by ‘Quiet’ or ‘Silence’).
Range: 0–255 (units of 0.1 second)
0 Silence detection disabled
50* Silence detection enabled
Table 25. Voice Mode Command Descriptions (Continued)
Command Default Description
NOTE: An asterisk (*) denotes the factory-default setting.