Intel MD566X - Manual (Page 100)

56K V.92 Data, Fax, and Voice Chipset
100 Intel Confidential Programmer’s Guide
+VTX none
Play Mode: This command causes the modem to start voice transmission (play-
back mode) and play back a previously recorded voice message.
Upon receiving the AT+VTX command, the modem responds to the DTE with a
“CONNECT” message at the current DTE-to-modem rate. It is important that the
UART’s DTE-to-modem rate be equal to or higher than the compression-
scheme-required UART data rate (for example, CL1 at 4800 samples/second re-
quires 57,600 bps). If the DTE-to-modem data rate is lower than the compres-
sion-scheme-required UART data rate, then data may be lost or the playback
message may be garbled. After receiving the “CONNECT” message, the DTE
then sends the voice file to the modem. To ensure that data is not overwritten, the
modem provides both hardware or software flow control with AT+FLO=n. The
modem also buffers the data to ensure steady voice delivery, even though the
voice data may be transferred from the DTE in bursts.
Playing mode is terminated when the data is exhausted and the modem receives
the two terminating characters <DLE><ETX> from the DTE. Upon detecting
<DLE><ETX>
, the modem issues an “OK” result code. After the modem’s internal
buffer is empty, it returns to the command mode.
To abort playback mode immediately without waiting for the modem to empty its
internal buffer, send <DLE><CAN><DLE><ETX>.The modem aborts playback
mode immediately in two other situations: during a AT+VIT=n time-out or a DTR
toggle. The modem immediately aborts playback mode if +VIT
≠0 and the modem
has not received any data or if the modem receives a <DLE><NUL> code before
the +VIT timer time-out. The modem then hangs up the line and switches to data
mode (+FCLASS=0). If the UART DTR signal is toggled from on-off-on, then the
modem follows the &Dn setting. If configured for &D2 or &D3, then the modem
immediately aborts playback mode, hangs up the line, and switches to data mode
(+FCLASS=0).
Note: The voice sampling rate and sampling mode must be the same values
used during record mode.
Table 6-1. Voice Mode Command Descriptions (Continued)